Python API for egg and script installation
==========================================

The easy_install module provides some functions to provide support for
egg and script installation.  It provides functionality at the python
level that is similar to easy_install, with a few exceptions:

- By default, we look for new packages *and* the packages that
  they depend on.  This is somewhat like (and uses) the --upgrade
  option of easy_install, except that we also upgrade required
  packages.

- If the highest-revision package satisfying a specification is
  already present, then we don't try to get another one.  This saves a
  lot of search time in the common case that packages are pegged to
  specific versions.

- If there is a develop egg that satisfies a requirement, we don't
  look for additional distributions.  We always give preference to
  develop eggs.

- Distutils options for building extensions can be passed.

Distribution installation
-------------------------

The easy_install module provides a function, install, for installing one
or more packages and their dependencies.  The install function takes 2
positional arguments:

- An iterable of setuptools requirement strings for the distributions
  to be installed, and

- A destination directory to install to and to satisfy requirements
  from.  The destination directory can be None, in which case, no new
  distributions are downloaded and there will be an error if the
  needed distributions can't be found among those already installed.

It supports a number of optional keyword arguments:

links
   A sequence of URLs, file names, or directories to look for
   links to distributions.

index
   The URL of an index server, or almost any other valid URL. :)

   If not specified, the Python Package Index,
   https://pypi.org/simple/, is used.  You can specify an
   alternate index with this option.  If you use the links option and
   if the links point to the needed distributions, then the index can
   be anything and will be largely ignored.  In the examples, here,
   we'll just point to an empty directory on our link server.  This
   will make our examples run a little bit faster.

path
   A list of additional directories to search for locally-installed
   distributions.

working_set
   An existing working set to be augmented with additional
   distributions, if necessary to satisfy requirements.  This allows
   you to call install multiple times, if necessary, to gather
   multiple sets of requirements.

newest
   A boolean value indicating whether to search for new distributions
   when already-installed distributions meet the requirement.  When
   this is true, the default, and when the destination directory is
   not None, then the install function will search for the newest
   distributions that satisfy the requirements.

versions
   A dictionary mapping project names to version numbers to be used
   when selecting distributions.  This can be used to specify a set of
   distribution versions independent of other requirements.

use_dependency_links
   A flag indicating whether to search for dependencies using the
   setup dependency_links metadata or not. If true, links are searched
   for using dependency_links in preference to other
   locations. Defaults to true.

relative_paths
   Adjust egg paths so they are relative to the script path.  This
   allows scripts to work when scripts and eggs are moved, as long as
   they are both moved in the same way.

allow_unknown_extras
    Install the requirements, even if one of them specifies an
    extra not provided by the distribution.

The install method returns a working set containing the distributions
needed to meet the given requirements.

We have a link server that has a number of eggs:

    >>> print_(get(link_server), end='')
    <html><body>
    <a href="bigdemo-0.1-py3-none-any.whl">bigdemo-0.1-py3-none-any.whl</a><br>
    <a href="demo-0.1-py3-none-any.whl">demo-0.1-py3-none-any.whl</a><br>
    <a href="demo-0.2-py3-none-any.whl">demo-0.2-py3-none-any.whl</a><br>
    <a href="demo-0.3-py3-none-any.whl">demo-0.3-py3-none-any.whl</a><br>
    <a href="demo-0.4rc1-py3-none-any.whl">demo-0.4rc1-py3-none-any.whl</a><br>
    <a href="demoneeded-1.0.tar.gz">demoneeded-1.0.tar.gz</a><br>
    <a href="demoneeded-1.1.tar.gz">demoneeded-1.1.tar.gz</a><br>
    <a href="demoneeded-1.2rc1.tar.gz">demoneeded-1.2rc1.tar.gz</a><br>
    <a href="du_zipped-1.0-pyN.N.egg">du_zipped-1.0-pyN.N.egg</a><br>
    <a href="extdemo-1.4.tar.gz">extdemo-1.4.tar.gz</a><br>
    <a href="index/">index/</a><br>
    <a href="mixedcase-0.5.tar.gz">mixedcase-0.5.tar.gz</a><br>
    <a href="other-1.0-py3-none-any.whl">other-1.0-py3-none-any.whl</a><br>
    </body></html>

Let's make a directory and install the demo egg to it, using the demo:

    >>> dest = tmpdir('sample-install')
    >>> import zc.buildout.easy_install
    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo==0.2'], dest,
    ...     links=[link_server], index=link_server+'index/')

We requested version 0.2 of the demo distribution to be installed into
the destination server.  We specified that we should search for links
on the link server and that we should use the (empty) link server
index directory as a package index.

The working set contains the distributions we retrieved.

    >>> for dist in ws:
    ...     print_(dist)
    demoneeded 1.1
    demo 0.2

We got demoneeded because it was a dependency of demo.

And the actual eggs were added to the eggs directory.

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demoneeded-1.1-py2.4.egg

If we remove the version restriction on demo, but specify a false
value for newest, no new distributions will be installed:

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest, links=[link_server], index=link_server+'index/',
    ...     newest=False)
    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demoneeded-1.1-py2.4.egg

If we leave off the newest option, we'll get an update for demo:

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest, links=[link_server], index=link_server+'index/')
    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demo-0.3-py2.4.egg
    d  demoneeded-1.1-py2.4.egg

Note that we didn't get the newest versions available.  There were
release candidates for newer versions of both packages. By default,
final releases are preferred.  We can change this behavior using the
prefer_final function:

    >>> zc.buildout.easy_install.prefer_final(False)
    True

The old setting is returned.

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest, links=[link_server], index=link_server+'index/')
    >>> for dist in ws:
    ...     print_(dist)
    demoneeded 1.2rc1
    demo 0.4rc1

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demo-0.3-py2.4.egg
    d  demo-0.4rc1-py2.4.egg
    d  demoneeded-1.1-py2.4.egg
    d  demoneeded-1.2rc1-py2.4.egg

Let's put the setting back to the default.

    >>> zc.buildout.easy_install.prefer_final(True)
    False


We can supply additional distributions.  We can also supply
specifications for distributions that would normally be found via
dependencies.  We might do this to specify a specific version.

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo', 'other', 'demoneeded==1.0'], dest,
    ...     links=[link_server], index=link_server+'index/')

    >>> for dist in ws:
    ...     print_(dist)
    demoneeded 1.0
    other 1.0
    demo 0.3

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demo-0.3-py2.4.egg
    d  demo-0.4rc1-py2.4.egg
    d  demoneeded-1.0-py2.4.egg
    d  demoneeded-1.1-py2.4.egg
    d  demoneeded-1.2rc1-py2.4.egg
    d  other-1.0-py2.4.egg

    >>> rmdir(dest)

Unknown extras
--------------

Attempting to install a requirement with an extra it doesn't provide
is an error.

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo[unknown_extra]'], dest, links=[link_server],
    ...     index=link_server+'index/')
    Traceback (most recent call last):
    ...
    UserError: Couldn't find the required extra...

We can pass the ``allow_unknown_extras`` argument to force the
installation to proceed.

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo[unknown_extra]'], dest, links=[link_server],
    ...     index=link_server+'index/',
    ...     allow_unknown_extras=True)

    >>> ls(dest)
    d  demo-0.3-py2.4.egg

    >>> rmdir(dest)

Case issues
-----------

Let's install an egg with case naming issues.
Specifically, the sdist file is lower case while the name of the package is uppercase.

Let's enable server logging to check that the lower case file is downloaded.

    >>> _ = get(link_server + 'enable_server_logging')
    GET 200 /enable_server_logging
    >>> ws = zc.buildout.easy_install.install(
    ...     ['MIXEDCASE'], dest,
    ...     links=[link_server], index=link_server+'index/')
    GET 404 /index/mixedcase/
    GET 404 /index/MIXEDCASE/
    GET 200 /mixedcase-0.5.tar.gz
    GET 200 /demoneeded-1.1.tar.gz

Let's check that the uppercase dist is installed.
setuptools 75.8.1+ reports the name in all lowercase, earlier versions showed it in uppercase.
So we compare lowercase.

    >>> for dist in ws:
    ...     print_(str(dist).lower())
    demoneeded 1.1
    mixedcase 0.5
    >>> ls(dest, lowercase_and_sort_output=True)
    d  demoneeded-1.1-py2.4.egg
    d  mixedcase-0.5-pyN.N.egg

And cleanup.

    >>> _ = get(link_server + 'disable_server_logging')
    >>> rmdir(dest)

Specifying version information independent of requirements
----------------------------------------------------------

Sometimes it's useful to specify version information independent of
normal requirements specifications.  For example, a buildout may need
to lock down a set of versions, without having to put put version
numbers in setup files or part definitions.  If a dictionary is passed
to the install function, mapping project names to version numbers,
then the versions numbers will be used.

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest, links=[link_server], index=link_server+'index/',
    ...     versions = dict(demo='0.2', demoneeded='1.0'))
    >>> [d.version for d in ws]
    ['1.0', '0.2']

In this example, we specified a version for demoneeded, even though we
didn't define a requirement for it.  The versions specified apply to
dependencies as well as the specified requirements.

If we specify a version that's incompatible with a requirement, then
we'll get an error:

    >>> from zope.testing.loggingsupport import InstalledHandler
    >>> handler = InstalledHandler('zc.buildout.easy_install')
    >>> import logging
    >>> logging.getLogger('zc.buildout.easy_install').propagate = False

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo >0.2'], dest, links=[link_server],
    ...     index=link_server+'index/',
    ...     versions = dict(demo='0.2', demoneeded='1.0'))
    Traceback (most recent call last):
    ...
    IncompatibleConstraintError: The requirement ('demo>0.2') is not allowed by your [versions] constraint (0.2)

    >>> print_(handler)
    zc.buildout.easy_install DEBUG
      Installing 'demo >0.2'.
    zc.buildout.easy_install INFO
      Version and requirements information containing demo:
      [versions] constraint on demo: 0.2
      Base installation request: 'demo >0.2'

    >>> handler.clear()

If no versions are specified, a debugging message will be output
reporting that a version was picked automatically:

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest, links=[link_server], index=link_server+'index/',
    ...     )

    >>> print_(handler) # doctest: +ELLIPSIS
    zc.buildout.easy_install DEBUG
      Installing 'demo'.
    zc.buildout.easy_install INFO
      Getting distribution for 'demo'.
    zc.buildout.easy_install DEBUG
      Fetching demo 0.3 from: http://.../demo-0.3-py3-none-any.whl
    zc.buildout.easy_install INFO
      Got demo 0.3.
    zc.buildout.easy_install DEBUG
      Picked: demo = 0.3
    zc.buildout.easy_install DEBUG
      Getting required 'demoneeded'
    zc.buildout.easy_install DEBUG
        required by demo 0.3.
    zc.buildout.easy_install INFO
      Getting distribution for 'demoneeded'.
    zc.buildout.easy_install DEBUG
      Fetching demoneeded 1.1 from: http://.../demoneeded-1.1.tar.gz
    zc.buildout.easy_install DEBUG
      Running pip install:...
    zc.buildout.easy_install INFO
      Got demoneeded 1.1.
    zc.buildout.easy_install DEBUG
      Picked: demoneeded = 1.1


    zc.buildout.easy_install DEBUG
      Installing 'demo'.
    zc.buildout.easy_install DEBUG
      We have the best distribution that satisfies 'demo'.
    zc.buildout.easy_install DEBUG
      Picked: demo = 0.3
    zc.buildout.easy_install DEBUG
      Getting required 'demoneeded'
    zc.buildout.easy_install DEBUG
        required by demo 0.3.
    zc.buildout.easy_install DEBUG
      We have the best distribution that satisfies 'demoneeded'.
    zc.buildout.easy_install DEBUG
      Picked: demoneeded = 1.1

    >>> handler.uninstall()
    >>> logging.getLogger('zc.buildout.easy_install').propagate = True

We can request that we get an error if versions are picked:

    >>> zc.buildout.easy_install.allow_picked_versions(False)
    True

(The old setting is returned.)

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest, links=[link_server], index=link_server+'index/',
    ...     )
    Traceback (most recent call last):
    ...
    UserError: Picked: demo = 0.3
    <BLANKLINE>
    The `demo` egg does not have a version pin and `allow-picked-versions = false`.
    <BLANKLINE>
    To resolve this, add
    <BLANKLINE>
        demo = 0.3
    <BLANKLINE>
    to the [versions] section,
    <BLANKLINE>
    OR set `allow-picked-versions = true`.

    >>> zc.buildout.easy_install.allow_picked_versions(True)
    False

The function default_versions can be used to get and set default
version information to be used when no version information is passes.
If called with an argument, it sets the default versions:

    >>> zc.buildout.easy_install.default_versions(dict(demoneeded='1'))
    ... # doctest: +ELLIPSIS
    {...}

It always returns the previous default versions.  If called without an
argument, it simply returns the default versions without changing
them:

    >>> zc.buildout.easy_install.default_versions()
    {'demoneeded': '1'}

So with the default versions set, we'll get the requested version even
if the versions option isn't used:

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest, links=[link_server], index=link_server+'index/',
    ...     )

    >>> [d.version for d in ws]
    ['0.3', '1.0']

Of course, we can unset the default versions by passing an empty
dictionary:

    >>> zc.buildout.easy_install.default_versions({})
    {'demoneeded': '1'}

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest, links=[link_server], index=link_server+'index/',
    ...     )

    >>> [d.version for d in ws]
    ['0.3', '1.1']

Dependency links
----------------

Setuptools allows metadata that describes where to search for package
dependencies. This option is called dependency_links. Buildout has its
own notion of where to look for dependencies, but it also uses the
setup tools dependency_links information if it's available.

Let's demo this by creating an egg that specifies dependency_links.

To begin, let's create a new egg repository. This repository hold a
newer version of the 'demoneeded' egg than the sample repository does.

    >>> repoloc = tmpdir('repo')
    >>> from zc.buildout.tests import create_egg
    >>> create_egg('demoneeded', '1.2', repoloc)
    >>> link_server2 = start_server(repoloc)

Turn on logging on this server so that we can see when eggs are pulled
from it.

    >>> _ = get(link_server2 + 'enable_server_logging')
    GET 200 /enable_server_logging

Now we can create an egg that specifies that its dependencies are
found on this server.

    >>> repoloc = tmpdir('repo2')
    >>> create_egg('hasdeps', '1.0', repoloc,
    ...            install_requires = "'demoneeded'",
    ...            dependency_links = [link_server2])

Let's add the egg to another repository.

    >>> link_server3 = start_server(repoloc)

Now let's install the egg.

    >>> example_dest = tmpdir('example-install')
    >>> workingset = zc.buildout.easy_install.install(
    ...     ['hasdeps'], example_dest,
    ...     links=[link_server3], index=link_server3+'index/')
    GET 200 /
    GET 200 /demoneeded-1.2-pyN.N.egg

The server logs show that the dependency was retrieved from the server
specified in the dependency_links.

Now let's see what happens if we provide two different ways to retrieve
the dependencies.

    >>> rmdir(example_dest)
    >>> example_dest = tmpdir('example-install')
    >>> workingset = zc.buildout.easy_install.install(
    ...     ['hasdeps'], example_dest, index=link_server+'index/',
    ...     links=[link_server, link_server3])
    GET 200 /
    GET 200 /demoneeded-1.2-pyN.N.egg

Once again the dependency is fetched from the logging server even
though it is also available from the non-logging server. This is
because the version on the logging server is newer and buildout
normally chooses the newest egg available.

If you wish to control where dependencies come from regardless of
dependency_links setup metadata use the 'use_dependency_links' option
to zc.buildout.easy_install.install().

    >>> rmdir(example_dest)
    >>> example_dest = tmpdir('example-install')
    >>> workingset = zc.buildout.easy_install.install(
    ...     ['hasdeps'], example_dest, index=link_server+'index/',
    ...     links=[link_server, link_server3],
    ...     use_dependency_links=False)

Notice that this time the dependency egg is not fetched from the
logging server. When you specify not to use dependency_links, eggs
will only be searched for using the links you explicitly provide.

Another way to control this option is with the
zc.buildout.easy_install.use_dependency_links() function. This
function sets the default behavior for the zc.buildout.easy_install()
function.

    >>> zc.buildout.easy_install.use_dependency_links(False)
    True

The function returns its previous setting.

    >>> rmdir(example_dest)
    >>> example_dest = tmpdir('example-install')
    >>> workingset = zc.buildout.easy_install.install(
    ...     ['hasdeps'], example_dest, index=link_server+'index/',
    ...     links=[link_server, link_server3])

It can be overridden by passing a keyword argument to the install
function.

    >>> rmdir(example_dest)
    >>> example_dest = tmpdir('example-install')
    >>> workingset = zc.buildout.easy_install.install(
    ...     ['hasdeps'], example_dest, index=link_server+'index/',
    ...     links=[link_server, link_server3],
    ...	    use_dependency_links=True)
    GET 200 /demoneeded-1.2-pyN.N.egg

To return the dependency_links behavior to normal call the function again.

    >>> zc.buildout.easy_install.use_dependency_links(True)
    False
    >>> rmdir(example_dest)
    >>> example_dest = tmpdir('example-install')
    >>> workingset = zc.buildout.easy_install.install(
    ...     ['hasdeps'], example_dest, index=link_server+'index/',
    ...     links=[link_server, link_server3])
    GET 200 /demoneeded-1.2-pyN.N.egg


Script generation
-----------------

The easy_install module provides support for creating scripts from
eggs.  It provides a function similar to setuptools except that it
provides facilities for baking a script's path into the script.  This
has two advantages:

- The eggs to be used by a script are not chosen at run time, making
  startup faster and, more importantly, deterministic.

- The script doesn't have to import pkg_resources because the logic
  that pkg_resources would execute at run time is executed at
  script-creation time.

The scripts method can be used to generate scripts. Let's create a
destination directory for it to place them in:

    >>> import tempfile
    >>> bin = tmpdir('bin')

Now, we'll use the scripts method to generate scripts in this directory
from the demo egg:

    >>> import sys
    >>> scripts = zc.buildout.easy_install.scripts(
    ...     ['demo'], ws, sys.executable, bin)

the three arguments we passed were:

1. A sequence of distribution requirements.  These are of the same
   form as setuptools requirements.  Here we passed a single
   requirement, for the version 0.1 demo distribution.

2. A working set,

3. The destination directory.

The bin directory now contains a generated script:

    >>> ls(bin)
    -  demo

The return value is a list of the scripts generated:

    >>> import os, sys
    >>> if sys.platform == 'win32':
    ...     scripts == [os.path.join(bin, 'demo.exe'),
    ...                 os.path.join(bin, 'demo-script.py')]
    ... else:
    ...     scripts == [os.path.join(bin, 'demo')]
    True

Note that in Windows, 2 files are generated for each script.  A script
file, ending in '-script.py', and an exe file that allows the script
to be invoked directly without having to specify the Python
interpreter and without having to provide a '.py' suffix.

The demo script run the entry point defined in the demo egg:

    >>> cat(bin, 'demo') # doctest: +NORMALIZE_WHITESPACE
    #!/usr/local/bin/python2.7
    <BLANKLINE>
    import sys
    sys.path[0:0] = [
      '/sample-install/demo-0.3-py2.4.egg',
      '/sample-install/demoneeded-1.1-py2.4.egg',
      ]
    <BLANKLINE>
    import eggrecipedemo
    <BLANKLINE>
    if __name__ == '__main__':
        sys.exit(eggrecipedemo.main())

Some things to note:

- The demo and demoneeded eggs are added to the beginning of sys.path.

- The module for the script entry point is imported and the entry
  point, in this case, 'main', is run.

Rather than requirement strings, you can pass tuples containing 3
strings:

  - A script name,

  - A module,

  - An attribute expression for an entry point within the module.

For example, we could have passed entry point information directly
rather than passing a requirement:

    >>> scripts = zc.buildout.easy_install.scripts(
    ...     [('demo', 'eggrecipedemo', 'main')], ws,
    ...     sys.executable, bin)

    >>> cat(bin, 'demo') # doctest: +NORMALIZE_WHITESPACE
    #!/usr/local/bin/python2.7
    <BLANKLINE>
    import sys
    sys.path[0:0] = [
      '/sample-install/demo-0.3-py2.4.egg',
      '/sample-install/demoneeded-1.1-py2.4.egg',
      ]
    <BLANKLINE>
    import eggrecipedemo
    <BLANKLINE>
    if __name__ == '__main__':
        sys.exit(eggrecipedemo.main())

Passing entry-point information directly is handy when using eggs (or
distributions) that don't declare their entry points, such as
distributions that aren't based on setuptools.

The interpreter keyword argument can be used to generate a script that can
be used to invoke the Python interactive interpreter with the path set
based on the working set.  This generated script can also be used to
run other scripts with the path set on the working set:

    >>> scripts = zc.buildout.easy_install.scripts(
    ...     ['demo'], ws, sys.executable, bin, interpreter='py')


    >>> ls(bin)
    -  demo
    -  py

    >>> if sys.platform == 'win32':
    ...     scripts == [os.path.join(bin, 'demo.exe'),
    ...                 os.path.join(bin, 'demo-script.py'),
    ...                 os.path.join(bin, 'py.exe'),
    ...                 os.path.join(bin, 'py-script.py')]
    ... else:
    ...     scripts == [os.path.join(bin, 'demo'),
    ...                 os.path.join(bin, 'py')]
    True

The py script simply runs the Python interactive interpreter with
the path set:

    >>> cat(bin, 'py') # doctest: +NORMALIZE_WHITESPACE +REPORT_NDIFF
    #!/usr/local/bin/python2.7
    <BLANKLINE>
    import sys
    <BLANKLINE>
    sys.path[0:0] = [
      '/sample-install/demo-0.3-pyN.N.egg',
      '/sample-install/demoneeded-1.1-pyN.N.egg',
      ]
    <BLANKLINE>
    _interactive = True
    if len(sys.argv) > 1:
        # The Python interpreter wrapper allows only some of the options that a
        # "regular" Python interpreter accepts.
        _options, _args = __import__("getopt").getopt(sys.argv[1:], 'Iic:m:')
        _interactive = False
        for (_opt, _val) in _options:
            if _opt == '-i':
                _interactive = True
            elif _opt == '-c':
                exec(_val)
            elif _opt == '-m':
                sys.argv[1:] = _args
                _args = []
                __import__("runpy").run_module(
                     _val, {}, "__main__", alter_sys=True)
            elif _opt == '-I':
                # Allow yet silently ignore the `-I` option. The original behaviour
                # for this option is to create an isolated Python runtime. It was
                # deemed acceptable to allow the option here as this Python wrapper
                # is isolated from the system Python already anyway.
                # The specific use-case that led to this change is how the Python
                # language extension for Visual Studio Code calls the Python
                # interpreter when initializing the extension.
                pass
    <BLANKLINE>
        if _args:
            sys.argv[:] = _args
            __file__ = _args[0]
            del _options, _args
            with open(__file__, 'U') as __file__f:
                exec(compile(__file__f.read(), __file__, "exec"))
    <BLANKLINE>
    if _interactive:
        del _interactive
        __import__("code").interact(banner="", local=globals())

If invoked with a script name and arguments, it will run that script, instead.

    >>> write('ascript', r'''
    ... "demo doc"
    ... import sys
    ... print_ = lambda *a: sys.stdout.write(' '.join(map(str, a))+'\n')
    ... print_(sys.argv)
    ... print_((__name__, __file__, __doc__))
    ... ''')
    >>> print_(system(join(bin, 'py')+' ascript a b c'), end='')
    ['ascript', 'a', 'b', 'c']
    ('__main__', 'ascript', 'demo doc')

You can also use the -m option to run a module:

    >>> print_(system(join(bin, 'py')+' -m pdb'), end='')
    ... # doctest: +ELLIPSIS
    usage: pdb...

    >>> print_(system(join(bin, 'py')+' -m pdb what'), end='')  # if you have pdbpp installed, this may fail.
    Error: what does not exist

An interpreter can also be generated without other eggs:

    >>> scripts = zc.buildout.easy_install.scripts(
    ...     [], [], sys.executable, bin, interpreter='py')
    >>> cat(bin, 'py') # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
    #!/usr/local/bin/python2.7
    <BLANKLINE>
    import sys
    <BLANKLINE>
    sys.path[0:0] = [
    <BLANKLINE>
      ]
    ...

An additional argument can be passed to define which scripts to install
and to provide script names. The argument is a dictionary mapping
original script names to new script names.

    >>> bin = tmpdir('bin2')
    >>> scripts = zc.buildout.easy_install.scripts(
    ...     ['demo'], ws, sys.executable, bin, dict(demo='run'))

    >>> if sys.platform == 'win32':
    ...     scripts == [os.path.join(bin, 'run.exe'),
    ...                 os.path.join(bin, 'run-script.py')]
    ... else:
    ...     scripts == [os.path.join(bin, 'run')]
    True
    >>> ls(bin)
    -  run

    >>> print_(system(os.path.join(bin, 'run')), end='')
    3 1

The scripts that are generated are made executable:

    >>> if sys.platform == 'win32':
    ...     os.access(os.path.join(bin, 'run.exe'), os.X_OK)
    ... else:
    ...     os.access(os.path.join(bin, 'run'), os.X_OK)
    True


Including extra paths in scripts
--------------------------------

We can pass a keyword argument, extra paths, to cause additional paths
to be included in the a generated script:

    >>> foo = tmpdir('foo')
    >>> scripts = zc.buildout.easy_install.scripts(
    ...    ['demo'], ws, sys.executable, bin, dict(demo='run'),
    ...    extra_paths=[foo])

    >>> cat(bin, 'run') # doctest: +NORMALIZE_WHITESPACE
    #!/usr/local/bin/python2.7
    <BLANKLINE>
    import sys
    sys.path[0:0] = [
      '/sample-install/demo-0.3-py2.4.egg',
      '/sample-install/demoneeded-1.1-py2.4.egg',
      '/foo',
      ]
    <BLANKLINE>
    import eggrecipedemo
    <BLANKLINE>
    if __name__ == '__main__':
        sys.exit(eggrecipedemo.main())

Providing script arguments
--------------------------

An "argument" keyword argument can be used to pass arguments to an
entry point.  The value passed is a source string to be placed between the
parentheses in the call:

    >>> scripts = zc.buildout.easy_install.scripts(
    ...    ['demo'], ws, sys.executable, bin, dict(demo='run'),
    ...    arguments='1, 2')

    >>> cat(bin, 'run') # doctest: +NORMALIZE_WHITESPACE
    #!/usr/local/bin/python2.7
    import sys
    sys.path[0:0] = [
      '/sample-install/demo-0.3-py2.4.egg',
      '/sample-install/demoneeded-1.1-py2.4.egg',
      ]
    <BLANKLINE>
    import eggrecipedemo
    <BLANKLINE>
    if __name__ == '__main__':
        sys.exit(eggrecipedemo.main(1, 2))

Passing initialization code
---------------------------

You can also pass script initialization code:

    >>> scripts = zc.buildout.easy_install.scripts(
    ...    ['demo'], ws, sys.executable, bin, dict(demo='run'),
    ...    arguments='1, 2',
    ...    initialization='import os\nos.chdir("foo")',
    ...    interpreter='py')

    >>> cat(bin, 'run') # doctest: +NORMALIZE_WHITESPACE
    #!/usr/local/bin/python2.7
    import sys
    sys.path[0:0] = [
      '/sample-install/demo-0.3-py2.4.egg',
      '/sample-install/demoneeded-1.1-py2.4.egg',
      ]
    <BLANKLINE>
    import os
    os.chdir("foo")
    <BLANKLINE>
    import eggrecipedemo
    <BLANKLINE>
    if __name__ == '__main__':
        sys.exit(eggrecipedemo.main(1, 2))

It will be included in interpreters too:

    >>> cat(bin, 'py') # doctest: +NORMALIZE_WHITESPACE +ELLIPSIS
    #!/usr/local/bin/python2.7
    <BLANKLINE>
    import sys
    <BLANKLINE>
    sys.path[0:0] = [
      '/sample-install/demo-0.3-py3.3.egg',
      '/sample-install/demoneeded-1.1-py3.3.egg',
      ]
    <BLANKLINE>
    import os
    os.chdir("foo")
    <BLANKLINE>
    <BLANKLINE>
    _interactive = True
    ...

Relative paths
--------------

Sometimes, you want to be able to move a buildout directory around and
have scripts still work without having to rebuild them.  We can
control this using the relative_paths option to install.  You need
to pass a common base directory of the scripts and eggs:

    >>> bo = tmpdir('bo')
    >>> ba = tmpdir('ba')
    >>> mkdir(bo, 'eggs')
    >>> mkdir(bo, 'bin')
    >>> mkdir(bo, 'other')

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], join(bo, 'eggs'), links=[link_server],
    ...     index=link_server+'index/')

    >>> scripts = zc.buildout.easy_install.scripts(
    ...    ['demo'], ws, sys.executable, join(bo, 'bin'), dict(demo='run'),
    ...    extra_paths=[ba, join(bo, 'bar'), bo],
    ...    interpreter='py',
    ...    relative_paths=bo)

    >>> cat(bo, 'bin', 'run')
    #!/usr/local/bin/python2.7
    <BLANKLINE>
    import os
    <BLANKLINE>
    join = os.path.join
    base = os.path.dirname(os.path.abspath(os.path.realpath(__file__)))
    base = os.path.dirname(base)
    <BLANKLINE>
    import sys
    sys.path[0:0] = [
      join(base, 'eggs/demoneeded-1.1-pyN.N.egg'),
      join(base, 'eggs/demo-0.3-pyN.N.egg'),
      '/ba',
      join(base, 'bar'),
      base,
      ]
    <BLANKLINE>
    import eggrecipedemo
    <BLANKLINE>
    if __name__ == '__main__':
        sys.exit(eggrecipedemo.main())

Note that the extra path we specified that was outside the directory
passed as relative_paths wasn't converted to a relative path.

Of course, running the script works:

    >>> print_(system(join(bo, 'bin', 'run')), end='')
    3 1

We specified an interpreter and its paths are adjusted too:

    >>> cat(bo, 'bin', 'py') # doctest: +NORMALIZE_WHITESPACE +REPORT_NDIFF
    #!/usr/local/bin/python2.7
    <BLANKLINE>
    import os
    <BLANKLINE>
    join = os.path.join
    base = os.path.dirname(os.path.abspath(os.path.realpath(__file__)))
    base = os.path.dirname(base)
    <BLANKLINE>
    import sys
    <BLANKLINE>
    sys.path[0:0] = [
      join(base, 'eggs/demoneeded-1.1-pyN.N.egg'),
      join(base, 'eggs/demo-0.3-pyN.N.egg'),
      '/ba',
      join(base, 'bar'),
      base,
      ]
    <BLANKLINE>
    <BLANKLINE>
    _interactive = True
    if len(sys.argv) > 1:
        # The Python interpreter wrapper allows only some of the options that a
        # "regular" Python interpreter accepts.
        _options, _args = __import__("getopt").getopt(sys.argv[1:], 'Iic:m:')
        _interactive = False
        for (_opt, _val) in _options:
            if _opt == '-i':
                _interactive = True
            elif _opt == '-c':
                exec(_val)
            elif _opt == '-m':
                sys.argv[1:] = _args
                _args = []
                __import__("runpy").run_module(
                     _val, {}, "__main__", alter_sys=True)
            elif _opt == '-I':
                # Allow yet silently ignore the `-I` option. The original behaviour
                # for this option is to create an isolated Python runtime. It was
                # deemed acceptable to allow the option here as this Python wrapper
                # is isolated from the system Python already anyway.
                # The specific use-case that led to this change is how the Python
                # language extension for Visual Studio Code calls the Python
                # interpreter when initializing the extension.
                pass
    <BLANKLINE>
        if _args:
            sys.argv[:] = _args
            __file__ = _args[0]
            del _options, _args
            with open(__file__, 'U') as __file__f:
                exec(compile(__file__f.read(), __file__, "exec"))
    <BLANKLINE>
    if _interactive:
        del _interactive
        __import__("code").interact(banner="", local=globals())


Installing distutils-style scripts
----------------------------------

Most python libraries use the console_scripts entry point nowadays.  But
several still have a ``scripts=['bin/something']`` in their setup() call.
Buildout also installs those:

    >>> distdir = tmpdir('distutilsscriptdir')
    >>> distbin = tmpdir('distutilsscriptbin')
    >>> ws = zc.buildout.easy_install.install(
    ...     ['other'], distdir,
    ...     links=[link_server], index=link_server+'index/')
    >>> scripts = zc.buildout.easy_install.scripts(
    ...     ['other'], ws, sys.executable, distbin)
    >>> ls(distbin)
    -  distutilsscript

Like for console_scripts, the output is a list of the scripts
generated. Likewise, on windows two files, an ``.exe`` and a script with
``-script.py`` appended, are generated:

    >>> import os, sys
    >>> if sys.platform == 'win32':
    ...     scripts == [os.path.join(distbin, 'distutilsscript.exe'),
    ...                 os.path.join(distbin, 'distutilsscript-script.py')]
    ... else:
    ...     scripts == [os.path.join(distbin, 'distutilsscript')]
    True

It also works for zipped eggs:

    >>> distdir2 = tmpdir('distutilsscriptdir2')
    >>> distbin2 = tmpdir('distutilsscriptbin2')
    >>> ws = zc.buildout.easy_install.install(
    ...     ['du_zipped'], distdir2,
    ...     links=[link_server], index=link_server+'index/')
    >>> scripts = zc.buildout.easy_install.scripts(
    ...     ['du_zipped'], ws, sys.executable, distbin2)
    >>> ls(distbin2)
    -  distutilsscript

Distutils copies the script files verbatim, apart from a line at the top that
looks like ``#!/usr/bin/python``, which gets replaced by the actual python
interpreter. Buildout does the same, but additionally also adds the sys.path
like for the console_scripts.

    >>> cat(distbin, 'distutilsscript')
    #!/usr/local/bin/python2.7
    # -*- coding: utf-8 -*-
    """Module docstring."""
    from __future__ import print_statement
    <BLANKLINE>
    <BLANKLINE>
    import sys
    sys.path[0:0] = [
      '/distutilsscriptdir/other-1.0-pyN.N.egg',
      ]
    <BLANKLINE>
    <BLANKLINE>
    import os
    import sys; sys.stdout.write("distutils!\n")

Note that there are several items that need to come first in such a script
*before* buildout's ``sys.path`` statements: a source encoding hint, a module
docstring and ``__future__`` imports. Buildout retains them in their proper
place by looking at the first non-future import and placing its ``sys.path``
statement before that.

Due to the nature of distutils scripts, buildout cannot pass arguments as
there's no specific method to pass them to.

In some cases, a python 3 ``__pycache__`` directory can end up in an internal
``EGG-INFO`` metadata directory, next to the script information we're looking
for. Buildout doesn't crash on that:

    >>> eggname = [name for name in os.listdir(distdir2)
    ...            if name.endswith('egg')][0]
    >>> scripts_metadata_dir = os.path.join(
    ...     distdir2, eggname, 'EGG-INFO', 'scripts')
    >>> os.mkdir(os.path.join(scripts_metadata_dir, '__dummy__'))
    >>> scripts = zc.buildout.easy_install.scripts(
    ...     ['du_zipped'], ws, sys.executable, distbin2)
    >>> ls(distbin2)
    -  distutilsscript

Installing develop eggs sadly means that setuptools doesn't record distutils
scripts in the metadata. We try to detect such scripts anyhow:

    >>> dev_distutils_dir = tmpdir('dev_distutils_dir')
    >>> dev_distutils_dest = tmpdir('dev_distutils_dest')
    >>> dev_eggs_dir = os.path.join(dev_distutils_dest, 'develop-eggs')
    >>> bin_dir = os.path.join(dev_distutils_dest, 'bin')
    >>> os.mkdir(dev_eggs_dir)
    >>> os.mkdir(bin_dir)
    >>> write(dev_distutils_dir, 'distutilsscript2',
    ...     '#!/usr/bin/python\n'
    ...     '# -*- coding: utf-8 -*-\n'
    ...     '"""Module docstring."""\n'
    ...     'from __future__ import print_statement\n'
    ...     'import os\n'
    ...     'import sys; sys.stdout.write("distutils!\\n")\n'
    ...     )
    >>> write(dev_distutils_dir, 'setup.py',
    ... '''
    ... from setuptools import setup
    ... setup(name="foo2",
    ...       scripts=['distutilsscript2'])
    ... ''')
    >>> zc.buildout.easy_install.develop(
    ...   dev_distutils_dir, dev_eggs_dir)
    '/dev_distutils_dest/develop-eggs/foo2.egg-link'
    >>> ws = zc.buildout.easy_install.working_set(
    ...     ['foo2'], sys.executable, [dev_eggs_dir])
    >>> scripts = zc.buildout.easy_install.scripts(
    ...     ['foo2'], ws, sys.executable, dest=bin_dir)
    >>> if sys.platform == 'win32':
    ...     scripts == [os.path.join(dev_distutils_dest, 'bin', 'distutilsscript2.exe'),
    ...                 os.path.join(dev_distutils_dest, 'bin', 'distutilsscript2-script.py')]
    ... else:
    ...     scripts == [os.path.join(dev_distutils_dest, 'bin', 'distutilsscript2')]
    True


Handling custom build options for extensions provided in source distributions
-----------------------------------------------------------------------------

Sometimes, we need to control how extension modules are built.  The
build function provides this level of control.  It takes a single
package specification, downloads a source distribution, and builds it
with specified custom build options.

The build function takes 3 positional arguments:

spec
   A package specification for a source distribution

dest
   A destination directory

build_ext
   A dictionary of options to be passed to the distutils build_ext
   command when building extensions.

It supports a number of optional keyword arguments:

links
   a sequence of URLs, file names, or directories to look for
   links to distributions,

index
   The URL of an index server, or almost any other valid URL. :)

   If not specified, the Python Package Index,
   https://pypi.org/simple/, is used.  You can specify an
   alternate index with this option.  If you use the links option and
   if the links point to the needed distributions, then the index can
   be anything and will be largely ignored.  In the examples, here,
   we'll just point to an empty directory on our link server.  This
   will make our examples run a little bit faster.

path
   A list of additional directories to search for locally-installed
   distributions.

newest
   A boolean value indicating whether to search for new distributions
   when already-installed distributions meet the requirement.  When
   this is true, the default, and when the destination directory is
   not None, then the install function will search for the newest
   distributions that satisfy the requirements.

versions
   A dictionary mapping project names to version numbers to be used
   when selecting distributions.  This can be used to specify a set of
   distribution versions independent of other requirements.


Our link server included a source distribution that includes a simple
extension, extdemo.c::

  #include <Python.h>
  #include <extdemo.h>

  static PyMethodDef methods[] = {};

  PyMODINIT_FUNC
  initextdemo(void)
  {
      PyObject *m;
      m = Py_InitModule3("extdemo", methods, "");
  #ifdef TWO
      PyModule_AddObject(m, "val", PyInt_FromLong(2));
  #else
      PyModule_AddObject(m, "val", PyInt_FromLong(EXTDEMO));
  #endif
  }

The extension depends on a system-dependent include file, extdemo.h,
that defines a constant, EXTDEMO, that is exposed by the extension.

We'll add an include directory to our sample buildout and add the
needed include file to it:

    >>> mkdir('include')
    >>> write('include', 'extdemo.h',
    ... """
    ... #define EXTDEMO 42
    ... """)

Now, we can use the build function to create an egg from the source
distribution:

    >>> zc.buildout.easy_install.build(
    ...   'extdemo', dest,
    ...   {'include_dirs': os.path.join(sample_buildout, 'include')},
    ...   links=[link_server], index=link_server+'index/')
    ['/sample-install/extdemo-1.4-py2.4-unix-i686.egg']

The function returns the list of eggs

Now if we look in our destination directory, we see we have an extdemo egg:

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demo-0.3-py2.4.egg
    d  demoneeded-1.0-py2.4.egg
    d  demoneeded-1.1-py2.4.egg
    d  extdemo-1.4-py2.4-unix-i686.egg

Let's update our link server with a new version of extdemo:

    >>> update_extdemo()
    >>> print_(get(link_server), end='')
    <html><body>
    <a href="bigdemo-0.1-py3-none-any.whl">bigdemo-0.1-py3-none-any.whl</a><br>
    <a href="demo-0.1-py3-none-any.whl">demo-0.1-py3-none-any.whl</a><br>
    <a href="demo-0.2-py3-none-any.whl">demo-0.2-py3-none-any.whl</a><br>
    <a href="demo-0.3-py3-none-any.whl">demo-0.3-py3-none-any.whl</a><br>
    <a href="demo-0.4rc1-py3-none-any.whl">demo-0.4rc1-py3-none-any.whl</a><br>
    <a href="demoneeded-1.0.tar.gz">demoneeded-1.0.tar.gz</a><br>
    <a href="demoneeded-1.1.tar.gz">demoneeded-1.1.tar.gz</a><br>
    <a href="demoneeded-1.2rc1.tar.gz">demoneeded-1.2rc1.tar.gz</a><br>
    <a href="du_zipped-1.0-pyN.N.egg">du_zipped-1.0-pyN.N.egg</a><br>
    <a href="extdemo-1.4.tar.gz">extdemo-1.4.tar.gz</a><br>
    <a href="extdemo-1.5.tar.gz">extdemo-1.5.tar.gz</a><br>
    <a href="index/">index/</a><br>
    <a href="mixedcase-0.5.tar.gz">mixedcase-0.5.tar.gz</a><br>
    <a href="other-1.0-py3-none-any.whl">other-1.0-py3-none-any.whl</a><br>
    </body></html>

The easy_install caches information about servers to reduce network
access. To see the update, we have to call the clear_index_cache
function to clear the index cache:

    >>> zc.buildout.easy_install.clear_index_cache()

If we run build with newest set to False, we won't get an update:

    >>> zc.buildout.easy_install.build(
    ...   'extdemo', dest,
    ...   {'include_dirs': os.path.join(sample_buildout, 'include')},
    ...   links=[link_server], index=link_server+'index/',
    ...   newest=False)
    ['/sample-install/extdemo-1.4-py2.4-linux-i686.egg']

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demo-0.3-py2.4.egg
    d  demoneeded-1.0-py2.4.egg
    d  demoneeded-1.1-py2.4.egg
    d  extdemo-1.4-py2.4-unix-i686.egg

But if we run it with the default True setting for newest, then we'll
get an updated egg:

    >>> zc.buildout.easy_install.build(
    ...   'extdemo', dest,
    ...   {'include_dirs': os.path.join(sample_buildout, 'include')},
    ...   links=[link_server], index=link_server+'index/')
    ['/sample-install/extdemo-1.5-py2.4-unix-i686.egg']

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demo-0.3-py2.4.egg
    d  demoneeded-1.0-py2.4.egg
    d  demoneeded-1.1-py2.4.egg
    d  extdemo-1.4-py2.4-unix-i686.egg
    d  extdemo-1.5-py2.4-unix-i686.egg

The versions option also influences the versions used.  For example,
if we specify a version for extdemo, then that will be used, even
though it isn't the newest.  Let's clean out the destination directory
first:

    >>> import os
    >>> for name in os.listdir(dest):
    ...     remove(dest, name)

    >>> zc.buildout.easy_install.build(
    ...   'extdemo', dest,
    ...   {'include_dirs': os.path.join(sample_buildout, 'include')},
    ...   links=[link_server], index=link_server+'index/',
    ...   versions=dict(extdemo='1.4'))
    ['/sample-install/extdemo-1.4-py2.4-unix-i686.egg']

    >>> ls(dest)
    d  extdemo-1.4-py2.4-unix-i686.egg

Handling custom build options for extensions in develop eggs
------------------------------------------------------------

The develop function is similar to the build function, except that,
rather than building an egg from a source directory containing a
setup.py script.

The develop function takes 2 positional arguments:

setup
   The path to a setup script, typically named "setup.py", or a
   directory containing a setup.py script.

dest
   The directory to install the egg link to

It supports some optional keyword argument:

build_ext
   A dictionary of options to be passed to the distutils build_ext
   command when building extensions.

We have a local directory containing the extdemo source:

    >>> contents = os.listdir(extdemo)
    >>> 'MANIFEST.in' in contents
    True
    >>> 'README' in contents
    True
    >>> 'extdemo.c' in contents
    True
    >>> 'setup.py' in contents
    True

Now, we can use the develop function to create a develop egg from the source
distribution:

    >>> zc.buildout.easy_install.develop(
    ...   extdemo, dest,
    ...   {'include_dirs': os.path.join(sample_buildout, 'include')})
    '/sample-install/extdemo.egg-link'

The name of the egg link created is returned.

Now if we look in our destination directory, we see we have an extdemo
egg link:

    >>> ls(dest)
    d  extdemo-1.4-py2.4-unix-i686.egg
    -  extdemo.egg-link

And that the source directory contains the compiled extension:

    >>> contents = os.listdir(extdemo)
    >>> bool([f for f in contents if f.endswith('.so') or f.endswith('.pyd')])
    True

Download cache
--------------

Normally, when distributions are installed, if any processing is
needed, they are downloaded from the internet to a temporary directory
and then installed from there.  A download cache can be used to avoid
the download step.  This can be useful to reduce network access and to
create source distributions of an entire buildout.

A download cache is specified by calling the download_cache
function.  The function always returns the previous setting. If no
argument is passed, then the setting is unchanged.  If an argument is
passed, the download cache is set to the given path, which must point
to an existing directory.  Passing None clears the cache setting.

To see this work, we'll create a directory and set it as the cache
directory:

    >>> cache = tmpdir('cache')
    >>> zc.buildout.easy_install.download_cache(cache)

We'll recreate our destination directory:

    >>> remove(dest)
    >>> dest = tmpdir('sample-install')

We'd like to see what is being fetched from the server, so we'll
enable server logging:

    >>> _ = get(link_server+'enable_server_logging')
    GET 200 /enable_server_logging

Now, if we install demo, and extdemo:

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo==0.2'], dest,
    ...     links=[link_server], index=link_server+'index/')
    GET 200 /
    GET 404 /index/demo/
    GET 200 /index/
    GET 200 /demo-0.2-py3-none-any.whl
    GET 404 /index/demoneeded/
    GET 200 /demoneeded-1.1.tar.gz

    >>> zc.buildout.easy_install.build(
    ...   'extdemo', dest,
    ...   {'include_dirs': os.path.join(sample_buildout, 'include')},
    ...   links=[link_server], index=link_server+'index/')
    GET 404 /index/extdemo/
    GET 200 /extdemo-1.5.tar.gz
    ['/sample-install/extdemo-1.5-py2.4-linux-i686.egg']

Not only will we get eggs in our destination directory:

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demoneeded-1.1-py2.4.egg
    d  extdemo-1.5-py2.4-linux-i686.egg

But we'll get distributions in the cache directory:

    >>> ls(cache)
    -  demo-0.2-py3-none-any.whl
    -  demoneeded-1.1.tar.gz
    -  extdemo-1.5.tar.gz

The cache directory contains uninstalled distributions, such as zipped
eggs or source distributions.

Let's recreate our destination directory and clear the index cache:

    >>> remove(dest)
    >>> dest = tmpdir('sample-install')
    >>> zc.buildout.easy_install.clear_index_cache()

Now when we install the distributions:

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo==0.2'], dest,
    ...     links=[link_server], index=link_server+'index/')
    GET 200 /
    GET 404 /index/demo/
    GET 200 /index/
    GET 404 /index/demoneeded/

    >>> zc.buildout.easy_install.build(
    ...   'extdemo', dest,
    ...   {'include_dirs': os.path.join(sample_buildout, 'include')},
    ...   links=[link_server], index=link_server+'index/')
    GET 404 /index/extdemo/
    ['/sample-install/extdemo-1.5-py2.4-linux-i686.egg']

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demoneeded-1.1-py2.4.egg
    d  extdemo-1.5-py2.4-linux-i686.egg

Note that we didn't download the distributions from the link server.

If we remove the restriction on demo, we'll download a newer version
from the link server:

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest,
    ...     links=[link_server], index=link_server+'index/')
    GET 200 /demo-0.3-py3-none-any.whl

Normally, the download cache is the preferred source of downloads, but
not the only one.

Installing solely from a download cache
---------------------------------------

A download cache can be used as the basis of application source
releases.  In an application source release, we want to distribute an
application that can be built without making any network accesses.  In
this case, we distribute a download cache and tell the easy_install
module to install from the download cache only, without making network
accesses.  The install_from_cache function can be used to signal that
packages should be installed only from the download cache.  The
function always returns the previous setting.  Calling it with no
arguments returns the current setting without changing it:

    >>> zc.buildout.easy_install.install_from_cache()
    False

Calling it with a boolean value changes the setting and returns the
previous setting:

    >>> zc.buildout.easy_install.install_from_cache(True)
    False

Let's remove demo-0.3-py2.4.egg from the cache, clear the index cache,
recreate the destination directory, and reinstall demo:

    >>> for  f in os.listdir(cache):
    ...     if f.startswith('demo-0.3-'):
    ...         remove(cache, f)

    >>> zc.buildout.easy_install.clear_index_cache()
    >>> remove(dest)
    >>> dest = tmpdir('sample-install')

    >>> ws = zc.buildout.easy_install.install(
    ...     ['demo'], dest,
    ...     links=[link_server], index=link_server+'index/')

    >>> ls(dest)
    d  demo-0.2-py2.4.egg
    d  demoneeded-1.1-py2.4.egg

This time, we didn't download from or even query the link server.

.. Disable the download cache:

    >>> zc.buildout.easy_install.download_cache(None)
    '/cache'

    >>> zc.buildout.easy_install.install_from_cache(False)
    True

Environment markers
-------------------

    Specifications can include PEP 496 environment markers.

    >>> _ = get(link_server + 'disable_server_logging')
    >>> spec = ["demo ==0.1; python_version < '3.10'",
    ... "demo == 0.2; python_version >= '3.10'"]
    >>> ws = zc.buildout.easy_install.install(
    ... spec, dest, links=[link_server], index=link_server+'index/')
    >>> demo_version = None
    >>> for egg in ws:
    ...     if egg.project_name == 'demo':
    ...         demo_version = egg.version
    >>> demo_version is not None
    True
    >>> if (sys.version_info.minor < 10):
    ...     demo_version
    ... else:
    ...     '0.1'
    '0.1'
    >>> if (sys.version_info.minor >= 10):
    ...     demo_version
    ... else:
    ...     '0.2'
    '0.2'


    Conflicts properly with version spec.

    >>> ws = zc.buildout.easy_install.install(
    ... spec, dest, links=[link_server], index=link_server+'index/',
    ... versions = dict(demo='0.3'))
    Traceback (most recent call last):
    ...
    zc.buildout.easy_install.IncompatibleConstraintError: The requirement ('demo==0...
