``ftputil`` -- a high-level FTP client library
==============================================

:Version:   5.0.3
:Date:      2022-01-26
:Summary:   high-level FTP client library for Python
:Keywords:  FTP, ``ftplib`` substitute, virtual filesystem, pure Python
:Author:    Stefan Schwarzer <sschwarzer@sschwarzer.net>

.. contents::


Introduction
------------

The ``ftputil`` module is a high-level interface to the ftplib_
module. The `FTPHost objects`_ generated from it allow many operations
similar to those of os_, `os.path`_ and `shutil`_.

.. _ftplib: https://docs.python.org/library/ftplib.html
.. _os: https://docs.python.org/library/os.html
.. _`os.stat`: https://docs.python.org/library/os.html#os.stat
.. _`os.path`: https://docs.python.org/library/os.path.html
.. _`shutil`: https://docs.python.org/library/shutil.html

Example::

    import ftputil

    # Download some files from the login directory.
    with ftputil.FTPHost("ftp.domain.com", "user", "password") as ftp_host:
        names = ftp_host.listdir(ftp_host.curdir)
        for name in names:
            if ftp_host.path.isfile(name):
                ftp_host.download(name, name)  # remote, local
        # Make a new directory and copy a remote file into it.
        ftp_host.mkdir("newdir")
        with ftp_host.open("index.html", "rb") as source:
            with ftp_host.open("newdir/index.html", "wb") as target:
                ftp_host.copyfileobj(source, target)  # similar to shutil.copyfileobj

Also, there are `FTPHost.lstat`_ and `FTPHost.stat`_ to request size and
modification time of a file. The latter can also follow links, similar
to `os.stat`_. `FTPHost.walk`_ and `FTPHost.path.walk`_ work, too.


``ftputil`` features
--------------------

* Method names are familiar from Python's ``os``, ``os.path`` and
  ``shutil`` modules. For example, use ``os.path.join`` to join
  paths for a local file system and ``ftp_host.path.join`` to join
  paths for a remote FTP file system.

* Remote file system navigation (``getcwd``, ``chdir``)

* Upload and download files (``upload``, ``upload_if_newer``,
  ``download``, ``download_if_newer``)

* Time zone synchronization between client and server (needed
  for ``upload_if_newer`` and ``download_if_newer``)

* Create and remove directories (``mkdir``, ``makedirs``, ``rmdir``,
  ``rmtree``) and remove files (``remove``)

* Get information about directories, files and links (``listdir``,
  ``stat``, ``lstat``, ``exists``, ``isdir``, ``isfile``, ``islink``,
  ``abspath``, ``dirname``, ``basename`` etc.)

* Iterate over remote file systems (``walk``)

* Local caching of results from ``lstat`` and ``stat`` calls to reduce
  network access (also applies to ``exists``, ``getmtime`` etc.).

* Read files from and write files to remote hosts via
  file-like objects (``FTPHost.open``; the generated file-like objects
  have the familiar methods like ``read``, ``readline``, ``readlines``,
  ``write``, ``writelines`` and ``close``. You can also iterate over
  these files line by line in a ``for`` loop.


Exception hierarchy
-------------------

The exceptions are in the namespace of the ``ftputil.error`` module, e. g.
``ftputil.error.TemporaryError``.

The exception classes are organized as follows::

    FTPError
        FTPOSError(FTPError, OSError)
            PermanentError(FTPOSError)
                CommandNotImplementedError(PermanentError)
            TemporaryError(FTPOSError)
        FTPIOError(FTPError)
        InternalError(FTPError)
            InaccessibleLoginDirError(InternalError)
            NoEncodingError(InternalError)
            ParserError(InternalError)
            RootDirError(InternalError)
            TimeShiftError(InternalError)

and are described here:

- ``FTPError``

  is the root of the exception hierarchy of the module.

- ``FTPOSError``

  is derived from ``OSError``. This is for similarity between the
  os module and ``FTPHost`` objects. Compare

  ::

    try:
        os.chdir("nonexisting_directory")
    except OSError:
        ...

  with

  ::

    host = ftputil.FTPHost("host", "user", "password")
    try:
        host.chdir("nonexisting_directory")
    except OSError:
        ...

  Imagine a function

  ::

    def func(path, file):
        ...

  which works on the local file system and catches ``OSErrors``. If you
  change the parameter list to

  ::

    def func(path, file, os=os):
        ...

  where ``os`` denotes the ``os`` module, you can call the function also as

  ::

    host = ftputil.FTPHost("host", "user", "password")
    func(path, file, os=host)

  to use the same code for both a local and remote file system.
  Another similarity between ``OSError`` and ``FTPOSError`` is that
  the latter holds the FTP server return code in the ``errno``
  attribute of the exception object and the error text in
  ``strerror``.

- ``PermanentError``

  is raised for 5xx return codes from the FTP server. This
  corresponds to ``ftplib.error_perm`` (though ``PermanentError`` and
  ``ftplib.error_perm`` are *not* identical).

- ``CommandNotImplementedError``

  indicates that an underlying command the code tries to use is not
  implemented. For an example, see the description of the
  `FTPHost.chmod`_ method.

- ``TemporaryError``

  is raised for FTP return codes from the 4xx category. This
  corresponds to ``ftplib.error_temp`` (though ``TemporaryError`` and
  ``ftplib.error_temp`` are *not* identical).

- ``FTPIOError``

  denotes an I/O error on the remote host. This appears
  mainly with file-like objects that are retrieved by calling
  ``FTPHost.open``. Compare

  ::

    >>> try:
    ...     f = open("not_there")
    ... except IOError as obj:
    ...     print(obj.errno)
    ...     print(obj.strerror)
    ...
    2
    No such file or directory

  with

  ::

    >>> ftp_host = ftputil.FTPHost("host", "user", "password")
    >>> try:
    ...     f = ftp_host.open("not_there")
    ... except IOError as obj:
    ...     print(obj.errno)
    ...     print(obj.strerror)
    ...
    550
    550 not_there: No such file or directory.

  As you can see, both code snippets are similar. However, the error
  codes aren't the same.

- ``InternalError``

  subsumes exception classes for signaling errors due to limitations
  of the FTP protocol or the concrete implementation of ``ftputil``.

- ``InaccessibleLoginDirError``

  This exception is raised if the directory in which "you" are placed
  upon login is not accessible, i. e. a ``chdir`` call with the
  directory as argument would fail.

- ``NoEncodingError``

  is raised if an FTP session instance doesn't have an ``encoding``
  attribute (see also `session factories`_).

- ``ParserError``

  is used for errors during the parsing of directory
  listings from the server. This exception is used by the ``FTPHost``
  methods ``stat``, ``lstat``, and ``listdir``.

- ``RootDirError``

  Because of the implementation of the ``lstat`` method it is not
  possible to do a ``stat`` call on the root directory ``/``.
  If you know *any* way to do it, please let me know. :-)

  This problem does *not* affect stat calls on items *in* the root
  directory.

- ``TimeShiftError``

  is used to denote errors which relate to setting the `time shift`_.


``FTPHost`` objects
-------------------

.. _`FTPHost construction`:

Construction
~~~~~~~~~~~~

Introduction
````````````

``FTPHost`` instances can be created with the following call::

    ftp_host = ftputil.FTPHost(server, user, password, account,
                               session_factory=ftplib.FTP)

The first four parameters are strings with the same meaning as for the
FTP class in the ``ftplib`` module. Usually the ``account`` and
``session_factory`` arguments aren't needed though.

``FTPHost`` objects can also be used in a ``with`` statement::

    import ftputil

    with ftputil.FTPHost(server, user, password) as ftp_host:
        print(ftp_host.listdir(ftp_host.curdir))

After the ``with`` block, the ``FTPHost`` instance and the
associated FTP sessions will be closed automatically.

If something goes wrong during the ``FTPHost`` construction or in the
body of the ``with`` statement, the instance is closed as well.
Exceptions will be propagated (as with ``try ... finally``).

.. _`session factory`:

Session factories
`````````````````

The keyword argument ``session_factory`` may be used to generate FTP
connections with other factories than the default ``ftplib.FTP``. For
example, the standard library of Python 3 contains a class
``ftplib.FTP_TLS`` which extends ``ftplib.FTP`` to use an encrypted
connection.

In fact, all positional and keyword arguments other than
``session_factory`` are passed to the factory to generate a new
background session. This also happens for every remote file that is
opened; see below.

This functionality of the constructor also allows to wrap
``ftplib.FTP`` objects to do something that wouldn't be possible with
the ``ftplib.FTP`` constructor alone.

As an example, assume you want to connect to another than the default
port, but ``ftplib.FTP`` only offers this by means of its ``connect``
method, not via its constructor. One solution is to use a custom
class as a session factory::

    import ftplib
    import ftputil

    EXAMPLE_PORT = 50001

    class MySession(ftplib.FTP):

        def __init__(self, host, userid, password, port):
            """Act like ftplib.FTP's constructor but connect to another port."""
            ftplib.FTP.__init__(self)
            self.connect(host, port)
            self.login(userid, password)

    # Try _not_ to use an _instance_ `MySession()` as factory, -
    # use the class itself.
    with ftputil.FTPHost(host, userid, password, port=EXAMPLE_PORT,
                         session_factory=MySession) as ftp_host:
        # Use `ftp_host` as usual.
        ...

On login, the format of the directory listings (needed for stat'ing
files and directories) should be determined automatically. If not,
please `enter a ticket`_.

.. _`enter a ticket`: https://ftputil.sschwarzer.net/issuetrackernotes

For the most common uses you don't need to create your own session
factory class though. The ``ftputil.session`` module has a function
``session_factory`` that can create session factories for a variety
of parameters::

    session_factory(base_class=ftplib.FTP,
                    port=21,
                    use_passive_mode=None,
                    encrypt_data_channel=True,
                    encoding=None,
                    debug_level=None)

with

- ``base_class`` is a base class to inherit a new session factory
  class from. By default, this is ``ftplib.FTP`` from the Python
  standard library.

- ``port`` is the command channel port. The default is 21, used in most
  FTP server configurations.

- ``use_passive_mode`` is either a boolean that determines whether
  passive mode should be used or ``None``. ``None`` means to let the
  base class choose active or passive mode.

- ``encrypt_data_channel`` defines whether to encrypt the data channel
  for secure connections. This is only supported for the base classes
  ``ftplib.FTP_TLS`` and ``M2Crypto.ftpslib.FTP_TLS``, otherwise the
  parameter is ignored.

- ``encoding`` can be a string to set the encoding of directory and
  file paths on the remote server. (This has nothing to do with the
  encoding of file contents!) If you pass a string and your base class
  is neither ``ftplib.FTP`` nor ``ftplib.FTP_TLS``, the used heuristic
  in ``session_factory`` may not work reliably. Therefore, if in
  doubt, let ``encoding`` be ``None`` and define your ``base_class``
  so that it sets the encoding you want.

  Note: In Python 3.9, the default path encoding for ``ftplib.FTP``
  and ``ftplib.FTP_TLS`` changed from previously "latin-1" to "utf-8".
  Hence, if you don't pass an ``encoding`` to ``session_factory``,
  you'll get different path encodings for Python 3.8 and earlier vs.
  Python 3.9 and later.

  If you're sure that you always use only ASCII characters in your
  remote paths, you don't need to worry about the path encoding and
  don't need to use the ``encoding`` argument.

- ``debug_level`` sets the debug level for FTP session instances. The
  semantics is defined by the base class. For example, a debug level
  of 2 causes the most verbose output for Python's ``ftplib.FTP``
  class.

All of these parameters can be combined. For example, you could use

::

    import ftplib

    import ftputil
    import ftputil.session


    my_session_factory = ftputil.session.session_factory(
                           base_class=ftpslib.FTP_TLS,
                           port=31,
                           encrypt_data_channel=True,
                           encoding="UTF-8",
                           debug_level=2)

    with ftputil.FTPHost(server, user, password,
                         session_factory=my_session_factory) as ftp_host:
        ...

to create and use a session factory derived from ``ftplib.FTP_TLS``
that connects on command channel 31, will encrypt the data channel,
use the UTF-8 encoding for remote paths and print output for debug
level 2.

Note: Generally, you can achieve everything you can do with
``ftputil.session.session_factory`` with an explicit session factory
as described at the start of this section.


Directory and file names
~~~~~~~~~~~~~~~~~~~~~~~~

.. note::

   Keep in mind that this section only applies to directory and file
   *names*, not file *contents*. Encoding and decoding for file
   contents is handled by the ``encoding`` argument for
   `FTPHost.open`_.

Generally, paths can be ``str`` or ``bytes`` objects (or `PathLike`_
objects wrapping ``str`` or ``bytes``). However, you can't mix
different string types (``bytes`` and ``str``) in one call (for
example in ``FTPHost.path.join``). If a method gets a string argument
(or a string argument wrapped in a PathLike_ object) and returns one
or more strings, these strings will have the same string type
(``bytes`` or ``str``) as the argument(s). Mixing different string
types in one call (for example in ``FTPHost.path.join``) isn't allowed
and will cause a ``TypeError``. These rules are the same as for local
file system operations.

.. _PathLike: https://docs.python.org/3/library/os.html#os.PathLike

Although you can pass paths as ``str`` or ``bytes``, the former is
recommended. See below for the reason.

*If* you have directory or file names with non-ASCII characters, you
need to be aware of the encoding the `session factory`_ (e. g.
``ftplib.FTP``) uses. This needs to be the same encoding that the FTP
server uses for the paths.

The following diagram shows string conversions on the way from your
code to the remote FTP server. The opposite way works analogously, so
encoding steps in the diagram become decoding steps and decoding steps
in the diagram become encoding steps.

Both "branching points" in the upper and lower part of diagrams are
independent, so depending on how you pass paths to ftputil and which
file system API the FTP server uses, there are four possible
combinations.

::

     +-----------+       +-----------+
     | Your code |       | Your code |
     +-----------+       +-----------+
          |                    |
          |  str               |  bytes
          v                    v
    +-------------+     +-------------+  decode with encoding of session,
    | ftputil API |     | ftputil API |  e. g. `ftplib.FTP` instance
    +-------------+     +-------------+
            \               /
             \     str     /
              v           v
            +---------------+  encode with encoding
            |  ftplib API   |  specified in `FTP` instance
            +---------------+
                    |
                    |  bytes
                    v
             +-------------+
             | socket API  |
             +-------------+
                /       \
               /         \                 local / client
    - - - - - / - - - - - \ - - - - - - - - - - - - - - - - - - - - - -
             /             \              remote / server
            /     bytes     \
           v                 v
    +------------+      +------------+  decode with encoding from
    | FTP server |      | FTP server |  FTP server configuration
    +------------+      +------------+
          |                   |
          |  bytes            |  str
          v                   v
   +-------------+      +-------------+
   | remote file |      | remote file |
   | system API  |      | system API  |
   +-------------+      +-------------+
           \                 /
            \      bytes    /
             v             v
          +-------------------+
          |    file system    |
          +-------------------+

As you can see at the top of the diagram, if you use ``str`` objects
(regular unicode strings), there's one fewer decoding step, and so one
fewer source of problems. If you use ``bytes`` objects for paths,
ftputil tries to get the encoding for the FTP server from the
``encoding`` attribute of the session instance (say, an instance of
``ftplib.FTP``). If no ``encoding`` attribute is present, a
``NoEncodingError`` is raised.

All encoding/decoding steps must use the same encoding, the encoding
the server uses (at the bottom of the diagram). If the server uses the
bytes from the socket directly, i. e. without an encoding step, you
have to use the file system encoding.

Until and including Python 3.8, the encoding implicitly assumed by
the ``ftplib`` module was latin-1, so using ``bytes`` was the safest
strategy. However, Python 3.9 made the ``encoding``
configurable via an ``ftplib.FTP`` constructor argument ``encoding``,
*but defaults to UTF-8*.

If you don't pass a `session factory`_ to the ``ftputil.FTPHost``
constructor, ftputil will use latin-1 encoding for the paths. This is
the same value as in earlier ftputil versions in combination with
Python 3.8 and earlier.

Summary:

- If possible, use only ASCII characters in paths.
- If possible, pass paths to ftputil as ``str``, not ``bytes``.
- If you use a custom session factory, the session instances created
  by the factory must have an ``encoding`` attribute with the name of
  the path encoding to use. If your session instances don't have an
  ``encoding`` attribute, ftputil raises a ``NoEncodingError`` when
  the session is created.


Hidden files and directories
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Whether ftputil sees "hidden" files and directories (usually files or
directories whose names start with a dot) depends on the FTP server
configuration. By default, ftputil does *not* use the ``-a`` option in
the FTP ``LIST`` command to find hidden files.

To tell the server to list hidden directories and files, set
``FTPHost.use_list_a_option`` to ``True``::

    ftp_host = ftputil.FTPHost(server, user, password, account,
                               session_factory=ftplib.FTP)
    ftp_host.use_list_a_option = True

Caveats:

- If the server doesn't understand the ``-a`` option at all, the
  server may interpret ``-a`` as the name of a file or directory,
  which can result in odd behavior. Therefore, use ``-a`` only if
  you're sure the server you're talking to supports it. Another
  approach is to have test code for ``-a`` support and fall back to
  not using the option.

- Even if the server knows about the ``-a`` option, the server may
  be configured to ignore it.

``FTPHost`` attributes and methods
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Attributes
``````````

- ``curdir``, ``pardir``, ``sep``

  are strings which denote the current and the parent directory on the
  remote server. ``sep`` holds the path separator. Though `RFC 959`_
  (File Transfer Protocol) notes that these values may depend on the
  FTP server implementation, the Unix variants seem to work well in
  practice, even for non-Unix servers.

  Nevertheless, it's recommended that you don't hardcode these values
  for remote paths, but use `FTPHost.path`_ as you would use
  ``os.path`` to write platform-independent Python code for local
  filesystems. Keep in mind that most, *but not all*, arguments of
  ``FTPHost`` methods refer to remote directories or files. For
  example, in `FTPHost.upload`_, the first argument is a local
  path and the second a remote path. Both of these should use their
  respective path separators.

.. _`FTPHost.upload`: `Uploading and downloading files`_

Remote file system navigation
`````````````````````````````

- ``getcwd()``

  returns the absolute current directory on the remote host. This
  method works like ``os.getcwd``.

- ``chdir(directory)``

  sets the current directory on the FTP server. This resembles
  ``os.chdir``, as you may have expected.

.. _`callback function`:

Uploading and downloading files
```````````````````````````````

- ``upload(source, target, callback=None)``

  copies a local source file (given by a filename, i. e. a string)
  to the remote host under the name target. Both ``source`` and
  ``target`` may be absolute paths or relative to their corresponding
  current directory (on the local or the remote host, respectively).

  The file content is always transferred in binary mode.

  The callback, if given, will be invoked for each transferred chunk
  of data::

    callback(chunk)

  where ``chunk`` is a bytestring. An example usage of a callback
  method is to display a progress indicator.

- ``download(source, target, callback=None)``

  performs a download from the remote source file to a local target
  file. Both ``source`` and ``target`` are strings. See the
  description of ``upload`` for more details.

.. _`upload_if_newer`:

- ``upload_if_newer(source, target, callback=None)``

  is similar to the ``upload`` method. The only difference is that the
  upload is only invoked if the time of the last modification for the
  source file is more recent than that of the target file or the
  target doesn't exist at all. The check for the last modification
  time considers the precision of the timestamps and transfers a file
  "if in doubt". Consequently the code

  ::

    ftp_host.upload_if_newer("source_file", "target_file")
    time.sleep(10)
    ftp_host.upload_if_newer("source_file", "target_file")

  might upload the file again if the timestamp of the target file is
  precise up to a minute, which is typically the case because the
  remote datetime is determined by parsing a directory listing from
  the server. To avoid unnecessary transfers, wait at least a minute
  between calls of ``upload_if_newer`` for the same file. If it still
  seems that a file is uploaded unnecessarily (or not when it should),
  read the subsection on `time shift`_ settings.

  If an upload actually happened, the return value of
  ``upload_if_newer`` is a ``True``, else ``False``.

  Note that the method only checks the existence and/or the
  modification time of the source and target file; it doesn't
  compare any other file properties, say, the file size.

  This also means that if a transfer is interrupted, the remote file
  will have a newer modification time than the local file, and thus
  the transfer won't be repeated if ``upload_if_newer`` is used a
  second time. There are at least two possibilities after a failed
  upload:

  - use ``upload`` instead of ``upload_if_newer``, or

  - remove the incomplete target file with ``FTPHost.remove``, then
    use ``upload`` or ``upload_if_newer`` to transfer it again.

.. _`download_if_newer`:

- ``download_if_newer(source, target, callback=None)``

  corresponds to ``upload_if_newer`` but performs a download from the
  server to the local host. Read the descriptions of download and
  ``upload_if_newer`` for more information. If a download actually
  happened, the return value is ``True``, else ``False``.

.. _`time shift`:
.. _`time zone correction`:

Time zone correction
````````````````````

For ``upload_if_newer`` and ``download_if_newer`` to work correctly,
the time zone of the server must be taken into account. By default,
ftputil assumes that the timestamps in server listings are in UTC_.

.. _UTC: https://en.wikipedia.org/wiki/Utc

.. _`set_time_shift`:

- ``set_time_shift(time_shift)``

  sets the so-called time shift value, measured in seconds. The time
  shift here is defined as the difference between the time used in
  server listings and UTC.

  ::

    time_shift = server_time - utc_time

  For example, a server in Berlin/Germany set to the local time
  (currently UTC+03:00), would require a time shift value of 3 *
  3600.0 = 10800.0 seconds to be handled correctly by ftputil's
  ``upload_if_newer`` and ``download_if_newer``, as well as the
  ``stat`` and ``lstat`` calls.

  Note that servers don't necessarily send their file system listings
  in their local time zone. Some use UTC, which actually makes sense
  because UTC doesn't lead to an ambiguity when there's a switch back
  from the daylight saving time to the "normal" time of the server
  location.

  If the time shift value is invalid, for example its absolute value
  is larger than 24 hours, a ``TimeShiftError`` is raised.

  .. note::

     Versions of ftputil before 4.0.0 used a different definition of
     "time shift", server_time - local_client_time.

     This had the advantage that the default of 0.0 would be correct
     *if* the server was set to the same time zone as the client
     where ftputil runs. On the other hand, this approach meant that
     the time shift depended on *two* time zones, not only the one
     used on the server side. This could be confusing if server
     and client *didn't* use the same time zone.

  See also `synchronize_times`_ for a way to set the time shift with a
  simple method call. If you can't use ``synchronize_times`` *and* the
  server uses the same time zone as the client, you can set the time
  shift value with

  ::

    set_time_shift(
      round( (datetime.datetime.now() - datetime.datetime.utcnow()).seconds, -2 )
    )

- ``time_shift()``

  returns the currently-set time shift value. See ``set_time_shift``
  above for its definition.

.. _`synchronize_times`:

- ``synchronize_times()``

  synchronizes the local times of the server and the client, so that
  `upload_if_newer`_ and `download_if_newer`_ work as expected, even
  if the client and the server use different time zones. For this
  to work, *all* of the following conditions must be true:

  - The connection between server and client is established.

  - The client has write access to the directory that is current when
    ``synchronize_times`` is called.

  If you can't fulfill these conditions, you can nevertheless set the
  time shift value explicitly with `set_time_shift`_. Trying to call
  ``synchronize_times`` if the above conditions aren't met results in
  a ``TimeShiftError`` exception.

Creating and removing directories
`````````````````````````````````

- ``mkdir(path, [mode])``

  makes the given directory on the remote host. This does *not*
  construct "intermediate" directories that don't already exist. The
  ``mode`` parameter is ignored; this is for compatibility with
  ``os.mkdir`` if an ``FTPHost`` object is passed into a function
  instead of the ``os`` module. See the explanation in the subsection
  `Exception hierarchy`_.

- ``makedirs(path, [mode], exist_ok=False)``

  works similar to ``mkdir`` (see above), but also makes intermediate
  directories like ``os.makedirs``. The ``mode`` parameter is only
  there for compatibility with ``os.makedirs`` and is ignored.

  ``exist_ok`` controls whether the existence of any directory but the
  last in the ``path`` should be considered an error. If the default
  ``False`` is used or passed to ``makedirs``, ftputil will raise a
  ``PermanentError`` if any directory but the last already exists.

- ``rmdir(path)``

  removes the given remote directory. If it's not empty, raise
  a ``PermanentError``.

- ``rmtree(path, ignore_errors=False, onerror=None)``

  removes the given remote, possibly non-empty, directory tree.
  The interface of this method is rather complex, in favor of
  compatibility with ``shutil.rmtree``.

  If ``ignore_errors`` is set to a true value, errors are ignored.
  If ``ignore_errors`` is a false value *and* ``onerror`` isn't
  set, all exceptions occurring during the tree iteration and
  processing are raised. These exceptions are all of type
  ``PermanentError``.

  To distinguish between different kinds of errors, pass in a callable
  for ``onerror``. This callable must accept three arguments:
  ``func``, ``path`` and ``exc_info``. ``func`` is a bound method
  object, *for example* ``your_host_object.listdir``. ``path`` is the
  path that was the recent argument of the respective method
  (``listdir``, ``remove``, ``rmdir``). ``exc_info`` is the exception
  info as it is gotten from ``sys.exc_info``.

  The code of ``rmtree`` is taken from Python's ``shutil`` module
  and adapted for ``ftputil``.

Removing files and links
````````````````````````

- ``remove(path)``

  removes a file or link on the remote host, similar to ``os.remove``.

- ``unlink(path)``

  is an alias for ``remove``.

Retrieving information about directories, files and links
`````````````````````````````````````````````````````````

- ``listdir(path)``

  returns a list containing the names of the files and directories
  in the given path, similar to `os.listdir`_. The special names
  ``.`` and ``..`` are not in the list.

The methods ``lstat`` and ``stat`` (and some others) rely on the
directory listing format used by the FTP server. When connecting to a
host, ``FTPHost``'s constructor tries to guess the right format, which
succeeds in most cases. However, if you get strange results or
``ParserError`` exceptions by a mere ``lstat`` call, please `enter a
ticket`_.

If ``lstat`` or ``stat`` give wrong modification dates or times, look
at the methods that deal with time zone differences (`time zone
correction`_).

.. _`FTPHost.lstat`:

- ``lstat(path)``

  returns an object similar to that from `os.lstat`_. This is a kind
  of tuple with additional attributes; see the documentation of the
  ``os`` module for details.

  The result is derived by parsing the output of a ``LIST`` command on
  the server. Therefore, the result from ``FTPHost.lstat`` can not
  contain more information than the received text. In particular:

  - User and group ids can only be determined as strings, not as
    numbers, and that only if the server supplies them. This is
    usually the case with Unix servers but maybe not for other FTP
    servers.

  - Values for the time of the last modification may be rough,
    depending on the information from the server. For timestamps
    older than a year, this usually means that the precision of the
    modification timestamp value is not better than a day. For newer
    files, the information may be accurate to a minute.

    If the time of the last modification is before the epoch (usually
    1970-01-01 UTC), set the time of the last modification to 0.0.

  - Links can only be recognized on servers that provide this
    information in the ``LIST`` output.

  - Stat attributes that can't be determined at all are set to
  	``None``. For example, a line of a directory listing may not
  	contain the date/time of a directory's last modification.

  - There's a special problem with stat'ing the root directory.
    (Stat'ing things *in* the root directory is fine though.) In
    this case, a ``RootDirError`` is raised. This has to do with the
    algorithm used by ``(l)stat``, and I know of no approach which
    mends this problem.

  Currently, ``ftputil`` recognizes the common Unix-style and
  Microsoft/DOS-style directory formats. If you need to parse output
  from another server type, please write to the `ftputil mailing
  list`_. You may consider `writing your own parser`_.

.. _`os.listdir`: https://docs.python.org/library/os.html#os.listdir
.. _`os.lstat`: https://docs.python.org/library/os.html#os.lstat
.. _`ftputil mailing list`: https://ftputil.sschwarzer.net/mailinglist
.. _`writing your own parser`: `Writing directory parsers`_

.. _`FTPHost.stat`:

- ``stat(path)``

  returns ``stat`` information also for files which are pointed to by a
  link. This method follows multiple links until a regular file or
  directory is found. If an infinite link chain is encountered or the
  target of the last link in the chain doesn't exist, a
  ``PermanentError`` is raised.

  The limitations of the ``lstat`` method also apply to ``stat``.

.. _`FTPHost.path`:

``FTPHost`` objects contain an attribute named ``path``, similar to
`os.path`_. The following methods can be applied to the remote host
with the same semantics as for ``os.path``:

::

    abspath(path)
    basename(path)
    commonprefix(path_list)
    dirname(path)
    exists(path)
    getmtime(path)
    getsize(path)
    isabs(path)
    isdir(path)
    isfile(path)
    islink(path)
    join(path1, path2, ...)
    normcase(path)
    normpath(path)
    split(path)
    splitdrive(path)
    splitext(path)
    walk(path, func, arg)

Like Python's counterparts under `os.path`_, ``ftputil``'s ``is...``
methods return ``False`` if they can't find the path given by their
argument.

Local caching of file system information
````````````````````````````````````````

Many of the above methods need access to the remote file system to
obtain data on directories and files. To get the most recent data,
*each* call to ``lstat``, ``stat``, ``exists``, ``getmtime`` etc.
would require to fetch a directory listing from the server, which can
make the program *very* slow. This effect is more pronounced for
operations which mostly scan the file system rather than transferring
file data.

For this reason, ``ftputil`` by default saves the results from
directory listings locally and reuses those results. This reduces
network accesses and so speeds up the software a lot. However, since
data is more rarely fetched from the server, the risk of obsolete data
also increases. This will be discussed below.

Caching can be controlled -- if necessary at all -- via the
``stat_cache`` object in an ``FTPHost``'s namespace. For example,
after calling

::

    ftp_host = ftputil.FTPHost(host, user, password)

the cache can be accessed as ``ftp_host.stat_cache``.

While ``ftputil`` usually manages the cache quite well, there are two
possible reasons for modifying cache parameters.

The first is when the number of possible entries is too low. You may
notice that when you are processing very large directories and the
program becomes much slower than before. It's common for code to read
a directory with ``listdir`` and then process the found directories
and files. This can also happen implicitly by a call to
``FTPHost.walk``. Since version 2.6 ``ftputil`` automatically
increases the cache size if directories with more entries than the
current maximum cache size are to be scanned. Most of the time, this
works fine.

However, if you need access to stat data for several directories at
the same time, you may need to increase the cache explicitly. This is
done by the ``resize`` method::

    ftp_host.stat_cache.resize(20000)

where the argument is the maximum number of ``lstat`` results to store
(the default is 5000, in versions before 2.6 it was 1000). Note that
each path on the server, e. g. "/home/schwa/some_dir", corresponds to
a single cache entry. Methods like ``exists`` or ``getmtime`` all
derive their results from a previously fetched ``lstat`` result.

The value 5000 above means that the cache will hold *at most* 5000
entries (unless increased automatically by an explicit or implicit
``listdir`` call, see above). If more are about to be stored, the
entries which haven't been used for the longest time will be deleted
to make place for newer entries.

The second possible reason to change the cache parameters is to avoid
stale cache data. Caching is so effective because it reduces network
accesses. This can also be a disadvantage if the file system data on
the remote server changes after a stat result has been retrieved; the
client, when looking at the cached stat data, will use obsolete
information.

There are two potential ways to get such out-of-date stat data. The
first happens when an ``FTPHost`` instance modifies a file path for
which it has a cache entry, e. g. by calling ``remove`` or ``rmdir``.
Such changes are handled transparently; the path will be deleted from
the cache. A different matter are changes unknown to the ``FTPHost``
object which inspects its cache. Obviously, for example, these are
changes by programs running on the remote host. On the other hand,
cache inconsistencies can also occur if two ``FTPHost`` objects change
a file system simultaneously::

    with (
      ftputil.FTPHost(server, user1, password1) as ftp_host1,
      ftputil.FTPHost(server, user1, password1) as ftp_host2
    ):
        stat_result1 = ftp_host1.stat("some_file")
        stat_result2 = ftp_host2.stat("some_file")
        ftp_host2.remove("some_file")
        # `ftp_host1` will still see the obsolete cache entry!
        print(ftp_host1.stat("some_file"))
        # Will raise an exception since an `FTPHost` object
        # knows of its own changes.
        print(ftp_host2.stat("some_file"))

At first sight, it may appear to be a good idea to have a shared cache
among several ``FTPHost`` objects. After some thinking, this turns out
to be very error-prone. For example, it won't help with different
processes using ``ftputil``. So, if you have to deal with concurrent
write/read accesses to a server, you have to handle them explicitly.

The most useful tool for this is the ``invalidate`` method. In the
example above, it could be used like this::

    with (
      ftputil.FTPHost(server, user1, password1) as ftp_host1,
      ftputil.FTPHost(server, user1, password1) as ftp_host2
    ):
        stat_result1 = ftp_host1.stat("some_file")
        stat_result2 = ftp_host2.stat("some_file")
        ftp_host2.remove("some_file")
        # Invalidate using an absolute path.
        absolute_path = ftp_host1.path.abspath(
                          ftp_host1.path.join(ftp_host1.getcwd(), "some_file"))
        ftp_host1.stat_cache.invalidate(absolute_path)
        # Will now raise an exception as it should.
        print(ftp_host1.stat("some_file"))
        # Would raise an exception since an `FTPHost` object
        # knows of its own changes, even without `invalidate`.
        print(ftp_host2.stat("some_file"))

The method ``invalidate`` can be used on any *absolute* path, be it a
directory, a file or a link.

By default, the cache entries (if not replaced by newer ones) are
stored for an infinite time. That is, if you start your Python process
using ``ftputil`` and let it run for three days a stat call may still
access cache data that old. To avoid this, you can set the ``max_age``
attribute::

    with ftputil.FTPHost(server, user, password) as ftp_host:
        ftp_host.stat_cache.max_age = 60 * 60  # = 3600 seconds

This sets the maximum age of entries in the cache to an hour. This
means any entry older won't be retrieved from the cache but its data
instead fetched again from the remote host and then again stored for
up to an hour. To reset `max_age` to the default of unlimited age,
i. e. cache entries never expire, use ``None`` as value.

If you are certain that the cache will be in the way, you can disable
and later re-enable it completely with ``disable`` and ``enable``::

    with ftputil.FTPHost(server, user, password) as ftp_host:
        ftp_host.stat_cache.disable()
        ...
        ftp_host.stat_cache.enable()

During that time, the cache won't be used; all data will be fetched
from the network. After enabling the cache again, its entries will be
the same as when the cache was disabled, that is, entries won't get
updated with newer data during this period. Note that even when the
cache is disabled, the file system data in the code can become
inconsistent::

    with ftputil.FTPHost(server, user, password) as ftp_host:
        ftp_host.stat_cache.disable()
        if ftp_host.path.exists("some_file"):
            mtime = ftp_host.path.getmtime("some_file")

In that case, the file ``some_file`` may have been removed by another
process between the calls to ``exists`` and ``getmtime``!

Iteration over directories
``````````````````````````

.. _`FTPHost.walk`:

- ``walk(top, topdown=True, onerror=None, followlinks=False)``

  iterates over a directory tree, similar to `os.walk`_. Actually,
  ``FTPHost.walk`` uses the code from Python with just the necessary
  modifications, so see the linked documentation.

.. _`os.walk`: https://docs.python.org/2/library/os.html#os.walk

.. _`FTPHost.path.walk`:

- ``path.walk(path, func, arg)``

  Similar to ``os.path.walk``, the ``walk`` method in
  `FTPHost.path`_ can be used, though ``FTPHost.walk`` is probably
  easier to use.

Other methods
`````````````

- ``close()``

  closes the connection to the remote host. After this, no more
  interaction with the FTP server is possible with this ``FTPHost``
  object. Usually you don't need to close an ``FTPHost`` instance
  with ``close`` if you set up the instance in a ``with`` statement.

- ``rename(source, target)``

  renames the source file (or directory) on the FTP server.

.. _`FTPHost.chmod`:

- ``chmod(path, mode)``

  sets the access mode (permission flags) for the given path. The mode
  is an integer as returned for the mode by the ``stat`` and ``lstat``
  methods. Be careful: Usually, mode values are written as octal
  numbers, for example 0755 to make a directory readable and writable
  for the owner, but not writable for the group and others. If you
  want to use such octal values, rely on Python's support for them::

    ftp_host.chmod("some_directory", 0o755)

  Not all FTP servers support the ``chmod`` command. In case of
  an exception, how do you know if the path doesn't exist or if
  the command itself is invalid? If the FTP server complies with
  `RFC 959`_, it should return a status code 502 if the ``SITE CHMOD``
  command isn't allowed. ``ftputil`` maps this special error
  response to a ``CommandNotImplementedError`` which is derived from
  ``PermanentError``.

  So you need to code like this::

    with ftputil.FTPHost(server, user, password) as ftp_host:
        try:
            ftp_host.chmod("some_file", 0o644)
        except ftputil.error.CommandNotImplementedError:
            # `chmod` not supported
            ...
        except ftputil.error.PermanentError:
            # Possibly a non-existent file
            ...

  Because the ``CommandNotImplementedError`` is more specific, you
  have to test for it first.

.. _`RFC 959`: `RFC 959 - File Transfer Protocol (FTP)`_

- ``copyfileobj(source, target, length=64*1024)``

  copies the contents from the file-like object ``source`` to the
  file-like object ``target``. The only difference to
  ``shutil.copyfileobj`` is the default buffer size. Note that
  arbitrary file-like objects can be used as arguments (e. g. local
  files, remote FTP files).

  However, the interfaces of ``source`` and ``target`` have to match;
  the string type read from ``source`` must be an accepted string type
  when written to ``target``. For example, if you open ``source`` in
  Python 3 as a local text file and ``target`` as a remote file object
  in binary mode, the transfer will fail since ``source.read`` gives
  unicode strings (``str``) whereas ``target.write`` only accepts byte
  strings (``bytes``).

  See `File-like objects`_ for the construction and use of remote
  file-like objects.

.. _`set_parser`:

- ``set_parser(parser)``

  sets a custom parser for FTP directories. Note that you have to pass
  in a parser *instance*, not the class.

  An `extra section`_ shows how to write own parsers if the default
  parsers in ``ftputil`` don't work for you.

.. _`extra section`: `Writing directory parsers`_

.. _`keep_alive`:

- ``keep_alive()``

  attempts to keep the connection to the remote server active in order
  to prevent timeouts from happening. This method is primarily
  intended to keep the underlying FTP connection of an ``FTPHost``
  object alive while a file is uploaded or downloaded. This will
  require either an extra thread while the upload or download is in
  progress or calling ``keep_alive`` from a `callback function`_.

  The ``keep_alive`` method won't help if the connection has already
  timed out. In this case, a ``ftputil.error.TemporaryError`` is raised.

  If you want to use this method, keep in mind that FTP servers define
  a timeout for a reason. A timeout prevents running out of server
  connections because of clients that never disconnect on their own.

  Note that the ``keep_alive`` method does *not* affect the "hidden"
  FTP child connections established by ``FTPHost.open`` (see section
  `FTPHost instances vs. FTP connections`_ for details). You *can't*
  use ``keep_alive`` to avoid a timeout in a stalling transfer like
  this::

      with ftputil.FTPHost(server, userid, password) as ftp_host:
          with ftp_host.open("some_remote_file", "rb") as fobj:
              data = fobj.read(100)
              # _Futile_ attempt to avoid file connection timeout.
              for i in range(15):
                  time.sleep(60)
                  ftp_host.keep_alive()
              # Will raise an `ftputil.error.TemporaryError`.
              data += fobj.read()


.. _`FTPHost.open`:

File-like objects
-----------------

Construction
~~~~~~~~~~~~

Basics
``````

``FTPFile`` objects are returned by a call to ``FTPHost.open``;
never use the ``FTPFile`` constructor directly.

The APIs for remote file-like objects is modeled after the APIs of
the built-in ``open`` function and its return value.

- ``FTPHost.open(path, mode="r", buffering=None, encoding=None,
  errors=None, newline=None, rest=None)``

  returns a file-like object that refers to the path on the remote
  host. This path may be absolute or relative to the current directory
  on the remote host (this directory can be determined with the
  ``getcwd`` method). As with local file objects, the default mode is
  "r", i. e. reading text files. Valid modes are "r", "rb", "w", and
  "wb".

  If a file is opened in binary mode, you *must not* specify an
  encoding. On the other hand, if you open a file in text mode, an
  encoding is used. By default, this is the return value of
  ``locale.getpreferredencoding``, but you can (and probably should)
  specify a distinct encoding.

  If you open a file in binary mode, the read and write operations use
  ``bytes`` objects. That is, read operations return ``bytes`` and
  write operations only accept ``bytes``.

  Similarly, text files always work with strings (``str``). Here, read
  operations return string and write operations only accept strings.

  The arguments ``buffering``, ``errors`` and ``newline`` have the
  same semantics as in open_.

  If the file is opened in binary mode, you may pass 0 or a positive
  integer for the ``rest`` argument. The argument is passed to the
  underlying FTP session instance (for example an instance of
  ``ftplib.FTP``) to start reading or writing at the given byte
  offset. For example, if a remote file contains the letters
  "abcdef" in ASCII encoding, ``rest=3`` will start reading at "d".

  .. warning::

     If you pass ``rest`` values which point *after* the file, the
     behavior is undefined and may even differ from one FTP server to
     another. Therefore, use the ``rest`` argument only for error
     recovery in case of interrupted transfers. You need to keep track
     of the transferred data so that you can provide a valid ``rest``
     argument for a resumed transfer.

.. _`open`: https://docs.python.org/3/library/functions.html#open

``FTPHost.open`` can also be used in a ``with`` statement::

    import ftputil

    with ftputil.FTPHost(...) as ftp_host:
        ...
        with ftp_host.open("new_file", "w", encoding="utf8") as fobj:
            fobj.write("This is some text.")

At the end of the ``with`` block, the remote file will be closed
automatically.

If something goes wrong during the construction of the file or in the
body of the ``with`` statement, the file will be closed as well.
Exceptions will be propagated as with ``try ... finally``.

Attributes and methods
~~~~~~~~~~~~~~~~~~~~~~

The methods

::

    close()
    read([count])
    readline([count])
    readlines()
    write(data)
    writelines(string_sequence)

and the attribute ``closed`` have the same semantics as for file
objects of a local disk file system. The iterator protocol is
supported as well, i. e. you can use a loop to read a file line by
line::

    with ftputil.FTPHost(server, user, password) as ftp_host:
        with ftp_host.open("some_file") as input_file:
            for line in input_file:
                # Do something with the line, e. g.
                print(line.strip().replace("ftplib", "ftputil"))

For more on file objects, see the section `File objects`_ in the
Python Library Reference.

.. _`file objects`: https://docs.python.org/3/glossary.html#term-file-object


.. _`child_connections`:

``FTPHost`` instances vs. FTP connections
-----------------------------------------

This section explains why keeping an ``FTPHost`` instance "alive"
without timing out sometimes isn't trivial. If you always finish your
FTP operations in time, you don't need to read this section.

The file transfer protocol is a stateful protocol. That means an FTP
connection always is in a certain state. Each of these states can only
change to certain other states under certain conditions triggered by
the client or the server.

One of the consequences is that a single FTP connection can't be used
at the same time, say, to transfer data on the FTP data channel and to
create a directory on the remote host.

For example, consider this::

    >>> import ftplib
    >>> ftp = ftplib.FTP(server, user, password)
    >>> ftp.pwd()
    '/'
    >>> # Start transfer. `CONTENTS` is a text file on the server.
    >>> socket = ftp.transfercmd("RETR CONTENTS")
    >>> socket
    <socket._socketobject object at 0x7f801a6386e0>
    >>> ftp.pwd()
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/usr/lib64/python2.7/ftplib.py", line 578, in pwd
        return parse257(resp)
      File "/usr/lib64/python2.7/ftplib.py", line 842, in parse257
        raise error_reply, resp
    ftplib.error_reply: 226-File successfully transferred
    226 0.000 seconds (measured here), 5.60 Mbytes per second
    >>>

Note that ``ftp`` is a single FTP connection, represented by an
``ftplib.FTP`` instance, not an ``ftputil.FTPHost`` instance.

On the other hand, consider this::

    >>> import ftputil
    >>> ftp_host = ftputil.FTPHost(server, user, password)
    >>> ftp_host.getcwd()
    >>> fobj = ftp_host.open("CONTENTS")
    >>> fobj
    <ftputil.file.FTPFile object at 0x7f8019d3aa50>
    >>> ftp_host.getcwd()
    u'/'
    >>> fobj.readline()
    u'Contents of FTP test directory\n'
    >>> fobj.close()
    >>>

To be able to start a file transfer (i. e. open a remote file for
reading or writing) and still be able to use other FTP commands,
ftputil uses a trick. For every remote file, ftputil creates a new FTP
connection, called a child connection in the ftputil source code.
(Actually, FTP connections belonging to closed remote files are
re-used if they haven't timed out yet.)

In most cases this approach isn't noticeable by code using ftputil.
However, the nice abstraction of dealing with a single FTP connection
falls apart if one of the child connections times out. For example, if
you open a remote file and work only with the initial "main"
connection to navigate the file system, the FTP connection for the
remote file may eventually time out.

While it's often relatively easy to prevent the "main" connection from
timing out it's unfortunately practically impossible to do this for a
remote file connection (apart from transferring some data, of course).
For this reason, `FTPHost.keep_alive`_ affects only the main
connection. Child connections may still time out if they're idle for
too long.

.. _`FTPHost.keep_alive`: `keep_alive`_

Some more details:

- A kind of "straightforward" way of keeping the main connection alive
  would be to call ``ftp_host.getcwd()``. However, this doesn't work
  because ftputil caches the current directory and returns it without
  actually contacting the server. That's the main reason why there's
  a ``keep_alive`` method since it calls ``pwd`` on the FTP connection
  (i. e. the session object), which isn't a public attribute.

- Some servers define not only an idle timeout but also a transfer
  timeout. This means the connection times out unless there's some
  transfer on the data channel for this connection. So ftputil's
  ``keep_alive`` doesn't prevent this timeout, but an
  ``ftp_host.listdir(ftp_host.curdir)`` call should do it. However,
  this transfers the data for the whole directory listing which might
  take some time if the directory has many entries.

Bottom line: If you can, you should organize your FTP actions so that
you finish everything before a timeout happens.


Writing directory parsers
-------------------------

``ftputil`` recognizes the two most widely-used FTP directory formats,
Unix and MS style, and adjusts itself automatically. Almost every FTP
server uses one of these formats.

However, if your server uses a format which is different from the two
provided by ``ftputil``, you can plug in a custom parser with a single
method call and have ``ftputil`` use this parser.

For this, you need to write a parser class by inheriting from the
class ``Parser`` in the ``ftputil.stat`` module. Here's an example::

    import ftputil.error
    import ftputil.stat

    class XyzParser(ftputil.stat.Parser):
        """
        Parse the default format of the FTP server of the XYZ
        corporation.
        """

        def parse_line(self, line, time_shift=0.0):
            """
            Parse a `line` from the directory listing and return a
            corresponding `StatResult` object. If the line can't
            be parsed, raise `ftputil.error.ParserError`.

            The `time_shift` argument can be used to fine-tune the
            parsing of dates and times. See the class
            `ftputil.stat.UnixParser` for an example.
            """
            # Split the `line` argument and examine it further; if
            # something goes wrong, raise an `ftputil.error.ParserError`.
            ...
            # Make a `StatResult` object from the parts above.
            stat_result = ftputil.stat.StatResult(...)
            # `_st_name`, `_st_target` and `_st_mtime_precision` are optional.
            stat_result._st_name = ...
            stat_result._st_target = ...
            stat_result._st_mtime_precision = ...
            return stat_result

        # Define `ignores_line` only if the default in the base class
        # doesn't do enough!
        def ignores_line(self, line):
            """
            Return a true value if the line should be ignored. For
            example, the implementation in the base class handles
            lines like "total 17". On the other hand, if the line
            should be used for stat'ing, return a false value.
            """
            is_total_line = super().ignores_line(line)
            my_test = ...
            return is_total_line or my_test

A ``StatResult`` object is similar to the value returned by
`os.stat`_ and is usually built with statements like

::

    stat_result = StatResult(
                    (st_mode, st_ino, st_dev, st_nlink, st_uid,
                     st_gid, st_size, st_atime, st_mtime, st_ctime))
    stat_result._st_name = ...
    stat_result._st_target = ...
    stat_result._st_mtime_precision = ...

with the arguments of the ``StatResult`` constructor described in
the following table.

===== =================== ============ =================== =======================
Index Attribute           os.stat type ``StatResult`` type Notes
===== =================== ============ =================== =======================
0     st_mode             int          int
1     st_ino              long         long
2     st_dev              long         long
3     st_nlink            int          int
4     st_uid              int          str                 usually only available as string
5     st_gid              int          str                 usually only available as string
6     st_size             long         long
7     st_atime            int/float    float
8     st_mtime            int/float    float
9     st_ctime            int/float    float
\-    _st_name            \-           str                 file name without directory part
\-    _st_target          \-           str                 link target (may be absolute or relative)
\-    _st_mtime_precision \-           int                 ``st_mtime`` precision in seconds
===== =================== ============ =================== =======================

If you can't extract all the desirable data from a line (for
example, the MS format doesn't contain any information about the
owner of a file), set the corresponding values in the ``StatResult``
instance to ``None``.

Parser classes can use several helper methods which are defined in
the class ``Parser``:

- ``parse_unix_mode`` parses strings like "drwxr-xr-x" and returns
  an appropriate ``st_mode`` integer value.

- ``parse_unix_time`` returns a float number usable for the
  ``st_...time`` values by parsing arguments like "Nov"/"23"/"02:33" or
  "May"/"26"/"2005". Note that the method expects the timestamp string
  already split at whitespace.

- ``parse_ms_time`` parses arguments like "10-23-01"/"03:25PM" and
  returns a float number like from ``time.mktime``. Note that the
  method expects the timestamp string already split at whitespace.

Additionally, there's an attribute ``_month_numbers`` which maps
lowercase three-letter month abbreviations to integers.

For more details, see the two "standard" parsers ``UnixParser`` and
``MSParser`` in the module ``ftputil/stat.py``.

To actually *use* the parser, call the method `set_parser`_ of the
``FTPHost`` instance.

If you can't write a parser or don't want to, please ask on the
`ftputil mailing list`_. Possibly someone has already written a parser
for your server or can help with it.


FAQ / Tips and tricks
---------------------

Where can I get the latest version?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

See the `download page`_. Announcements will be sent to the `mailing
list`_. Announcements on major updates will also be posted to the
`Python announcements list`_.

.. _`download page`: https://ftputil.sschwarzer.net/download
.. _`mailing list`: https://ftputil.sschwarzer.net/mailinglist
.. _`Python announcements list`: https://mail.python.org/mailman3/lists/python-announce-list.python.org/

Is there a mailing list on ``ftputil``?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Yes, please visit https://ftputil.sschwarzer.net/mailinglist to
subscribe or read the archives.

Though you can *technically* post without subscribing first I can't
recommend it: The mails from non-subscribers have to be approved by
me and because the arriving mails contain *lots* of spam, I rarely go
through these mails.

I found a bug! What now?
~~~~~~~~~~~~~~~~~~~~~~~~

Before reporting a bug, make sure that you already read this manual
and tried the `latest version`_ of ``ftputil``. There the bug might
have already been fixed.

.. _`latest version`: https://ftputil.sschwarzer.net/download

Please see https://ftputil.sschwarzer.net/issuetrackernotes for
guidelines on entering a bug in ``ftputil``'s ticket system. If you
are unsure if the behaviour you found is a bug or not, you should write
to the `ftputil mailing list`_. *Never* include confidential information
(user id, password, file names, etc.) in the problem report! Be
careful!

Does ``ftputil`` support TLS?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

``ftputil`` has no *built-in* TLS support.

On the other hand, there are two ways to get TLS support with
ftputil:

- The ``ftplib`` library has a class ``FTP_TLS`` that you can use for
  the ``session_factory`` keyword argument in the ``FTPHost``
  constructor. You can't use the class directly though *if* you need
  additional setup code in comparison to ``ftplib.FTP``, for example
  calling ``prot_p``, to secure the data connection. On the other
  hand, `ftputil.session.session_factory`_ can be used to create a
  custom session factory.

- If you have other requirements that ``session_factory`` can't
  fulfill, you may create your own session factory by inheriting from
  ``ftplib.FTP_TLS``::

    import ftplib

    import ftputil


    class FTPTLSSession(ftplib.FTP_TLS):

        def __init__(self, host, user, password):
            ftplib.FTP_TLS.__init__(self)
            self.connect(host, port)
            self.login(user, password)
            # Set up encrypted data connection.
            self.prot_p()
            ...

    # Note the `session_factory` parameter. Pass the class, not
    # an instance.
    with ftputil.FTPHost(server, user, password,
                         session_factory=FTPTLSSession) as ftp_host:
        # Use `ftp_host` as usual.
        ...

.. _`ftputil.session.session_factory`: `Session factories`_


How do I connect to a non-default port?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By default, an instantiated ``FTPHost`` object connects on the usual
FTP port. If you have to use a different port, refer to the section
`Session factories`_.

How do I set active or passive mode?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Please see the section `Session factories`_.

How can I debug an FTP connection problem?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can do this with a session factory. See `Session factories`_.

If you want to change the debug level only temporarily after the
connection is established, you can reach the `session object`_ as the
``_session`` attribute of the ``FTPHost`` instance and call
``_session.set_debuglevel``. Note that the ``_session`` attribute
should *only* be accessed for debugging. Calling arbitrary
``ftplib.FTP`` methods on the session object may *cause* bugs!

.. _`session object`: `Session factories`_

Conditional upload/download to/from a server in a different time zone
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You may find that ``ftputil`` uploads or downloads files
unnecessarily, or not when it should. Please see the section on `time
zone correction`_. It may even be sufficient to call
`synchronize_times`_.

When I use ``ftputil``, all I get is a ``ParserError`` exception
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The FTP server you connect to may use a directory format that
``ftputil`` doesn't understand. You can either write and
`plug in your own parser`_ or ask on the `mailing list`_ for
help.

.. _`plug in your own parser`: `Writing directory parsers`_

``isdir``, ``isfile`` or ``islink`` incorrectly return ``False``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Like Python's counterparts under `os.path`_, ``ftputil``'s methods
return ``False`` if they can't find the given path.

Probably you used ``listdir`` on a directory and called ``is...()`` on
the returned names. But if the argument for ``listdir`` wasn't the
current directory, the paths won't be found and so all ``is...()``
variants will return ``False``.

I don't find an answer to my problem in this document
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Please send an email with your problem report or question to the
`ftputil mailing list`_, and we'll see what we can do for you. :-)


Bugs and limitations
--------------------

- ``ftputil`` needs at least Python 3.6 to work.

- Whether ``ftputil`` "sees" "hidden" directory and file names (i. e.
  names starting with a dot) depends on the configuration of the FTP
  server. See `Hidden files and directories`_ for details.

- Due to the implementation of ``lstat`` it can not return a sensible
  value for the root directory ``/`` though stat'ing entries *in* the
  root directory isn't a problem. If you know an implementation that
  can do this, please let me know. The root directory is handled
  appropriately in ``FTPHost.path.exists/isfile/isdir/islink``, though.

- In multithreaded programs, you can have each thread use one or more
  ``FTPHost`` instances as long as no instance is shared with other
  threads.

- Currently, it is not possible to continue an interrupted upload or
  download. Contact me if this causes problems for you.

- There's exactly one cache for ``lstat`` results for each ``FTPHost``
  object, i. e. there's no sharing of cache results determined by
  several ``FTPHost`` objects. See `Local caching of file system
  information`_ for the reasons.


Files
-----

If not overwritten via installation options, the ``ftputil`` files
reside in the ``ftputil`` package. There's also documentation in
`reStructuredText`_ and in HTML format. The locations of these
files after installation is system-dependent.

.. _`reStructuredText`: https://docutils.sourceforge.net/rst.html

The files ``test_*.py`` and ``scripted_session.py`` are for
unit-testing. If you only *use* ``ftputil``, i. e. *don't* modify it,
you can delete these files.


References
----------

- Postel J, Reynolds J. 1985. `RFC 959 - File Transfer Protocol (FTP)`_.

- Python Software Foundation. 2020. `The Python Standard Library`_.

.. _`RFC 959 - File Transfer Protocol (FTP)`: https://www.ietf.org/rfc/rfc959.txt
.. _`The Python Standard Library`: https://docs.python.org/library/index.html


Authors
-------

``ftputil`` is written by Stefan Schwarzer
<sschwarzer@sschwarzer.net> and contributors (see
``doc/contributors.txt``).

The original ``lrucache`` module was written by Evan Prodromou
<evan@prodromou.name>.

Feedback is appreciated. :-)
