# Six: Python 2 and 3 Compatibility Library

Six provides simple utilities for wrapping over differences between Python 2 and Python 3. It is intended to support codebases that work on both Python 2 and 3 without modification. six consists of only one Python file, so it is painless to copy into a project.

Six can be downloaded on PyPI. Its bug tracker and code hosting is on GitHub.

The name, “six”, comes from the fact that 2*3 equals 6. Why not addition? Multiplication is more powerful, and, anyway, “five” has already been snatched away by the (admittedly now moribund) Zope Five project.

## Indices and tables

- Index

- Search Page

## Package contents

six.PY2

  A boolean indicating if the code is running on Python 2.

six.PY3

  A boolean indicating if the code is running on Python 3.

### Constants

Six provides constants that may differ between Python versions. Ones ending `_types` are mostly useful as the second argument to `isinstance` or `issubclass`.

six.class_types

  Possible class types. In Python 2, this encompasses old-style `py2:types.ClassType` and new-style `type` classes. In Python 3, this is just `type`.

six.integer_types

  Possible integer types. In Python 2, this is `py2:long()` and `py2:int()`, and in Python 3, just `py3:int()`.

six.string_types

  Possible types for text data. This is `py2:basestring()` in Python 2 and `py3:str()` in Python 3.

six.text_type

  Type for representing (Unicode) textual data. This is `py2:unicode()` in Python 2 and `py3:str()` in Python 3.

six.binary_type

  Type for representing binary data. This is `py2:str()` in Python 2 and `py3:bytes()` in Python 3. Python 2.6 and 2.7 include `bytes` as a builtin alias of `str`, so six’s version is only necessary for Python 2.5 compatibility.

six.MAXSIZE

  The maximum size of a container like `py3:list()` or `py3:dict()`. This is equivalent to `py3:sys.maxsize` in Python 2.6 and later (including 3.x). Note, this is temptingly similar to, but not the same as `py2:sys.maxint` in Python 2. There is no direct equivalent to `py2:sys.maxint` in Python 3 because its integer type has no limits aside from memory.

Here’s example usage of the module:

    import six

    def dispatch_types(value):
        if isinstance(value, six.integer_types):
            handle_integer(value)
        elif isinstance(value, six.class_types):
            handle_class(value)
        elif isinstance(value, six.string_types):
            handle_string(value)

### Object model compatibility

Python 3 renamed the attributes of several interpreter data structures. The following accessors are available. Note that the recommended way to inspect functions and methods is the stdlib `py3:inspect` module.

six.get_unbound_function(meth)

  Get the function out of unbound method meth. In Python 3, unbound methods don’t exist, so this function just returns meth unchanged. Example usage:

      from six import get_unbound_function

      class X(object):
          def method(self):
              pass
      method_function = get_unbound_function(X.method)

six.get_method_function(meth)

  Get the function out of method object meth.

six.get_method_self(meth)

  Get the `self` of bound method meth.

six.get_function_closure(func)

  Get the closure (list of cells) associated with func. This is equivalent to `func.__closure__` on Python 2.6+ and `func.func_closure` on Python 2.5.

six.get_function_code(func)

  Get the code object associated with func. This is equivalent to `func.__code__` on Python 2.6+ and `func.func_code` on Python 2.5.

six.get_function_defaults(func)

  Get the defaults tuple associated with func. This is equivalent to `func.__defaults__` on Python 2.6+ and `func.func_defaults` on Python 2.5.

six.get_function_globals(func)

  Get the globals of func. This is equivalent to `func.__globals__` on Python 2.6+ and `func.func_globals` on Python 2.5.

six.next(it)
six.advance_iterator(it)

  Get the next item of iterator it. `py3:StopIteration` is raised if the iterator is exhausted. This is a replacement for calling `it.next()` in Python 2 and `next(it)` in Python 3. Python 2.6 and above have a builtin `next` function, so six’s version is only necessary for Python 2.5 compatibility.

six.callable(obj)

  Check if obj can be called. Note `callable` has returned in Python 3.2, so using six’s version is only necessary when supporting Python 3.0 or 3.1.

six.iterkeys(dictionary, **kwargs)

  Returns an iterator over dictionary's keys. This replaces `dictionary.iterkeys()` on Python 2 and `dictionary.keys()` on Python 3. kwargs are passed through to the underlying method.

six.itervalues(dictionary, **kwargs)

  Returns an iterator over dictionary's values. This replaces `dictionary.itervalues()` on Python 2 and `dictionary.values()` on Python 3. kwargs are passed through to the underlying method.

six.iteritems(dictionary, **kwargs)

  Returns an iterator over dictionary's items. This replaces `dictionary.iteritems()` on Python 2 and `dictionary.items()` on Python 3. kwargs are passed through to the underlying method.

six.iterlists(dictionary, **kwargs)

  Calls `dictionary.iterlists()` on Python 2 and `dictionary.lists()` on Python 3. No builtin Python mapping type has such a method; this method is intended for use with multi-valued dictionaries like Werkzeug’s. kwargs are passed through to the underlying method.

six.viewkeys(dictionary)

  Return a view over dictionary's keys. This replaces `py2:dict.viewkeys()` on Python 2.7 and `py3:dict.keys()` on Python 3.

six.viewvalues(dictionary)

  Return a view over dictionary's values. This replaces `py2:dict.viewvalues()` on Python 2.7 and `py3:dict.values()` on Python 3.

six.viewitems(dictionary)

  Return a view over dictionary's items. This replaces `py2:dict.viewitems()` on Python 2.7 and `py3:dict.items()` on Python 3.

six.create_bound_method(func, obj)

  Return a method object wrapping func and bound to obj. On both Python 2 and 3, this will return a `py3:types.MethodType()` object. The reason this wrapper exists is that on Python 2, the `MethodType` constructor requires the obj’s class to be passed.

six.create_unbound_method(func, cls)

  Return an unbound method object wrapping func. In Python 2, this will return a `py2:types.MethodType()` object. In Python 3, unbound methods do not exist and this wrapper will simply return func.

class six.Iterator

  A class for making portable iterators. The intention is that it be subclassed and subclasses provide a `__next__` method. In Python 2, `Iterator` has one method: `next`. It simply delegates to `__next__`. An alternate way to do this would be to simply alias `next` to `__next__`. However, this interacts badly with subclasses that override `__next__`. `Iterator` is empty on Python 3. (In fact, it is just aliased to `py3:object`.)

@six.wraps(wrapped, assigned=functools.WRAPPER_ASSIGNMENTS, updated=functools.WRAPPER_UPDATES)

  This is Python 3.2’s `py3:functools.wraps()` decorator. It sets the `__wrapped__` attribute on what it decorates. It doesn’t raise an error if any of the attributes mentioned in `assigned` and `updated` are missing on `wrapped` object.

### Syntax compatibility

These functions smooth over operations which have different syntaxes between Python 2 and 3.

six.exec_(code, globals=None, locals=None)

  Execute code in the scope of globals and locals. code can be a string or a code object. If globals or locals are not given, they will default to the scope of the caller. If just globals is given, it will also be used as locals.

  Note

  Python 3’s `py3:exec()` doesn’t take keyword arguments, so calling `exec()` with them should be avoided.

six.print_(*args, *, file=sys.stdout, end="\\n", sep=" ", flush=False)

  Print args into file. Each argument will be separated with sep and end will be written to the file after the last argument is printed. If flush is true, `file.flush()` will be called after all data is written.

  Note

  In Python 2, this function imitates Python 3’s `py3:print()` by not having softspace support. If you don’t know what that is, you’re probably ok. :)

six.raise_from(exc_value, exc_value_from)

  Raise an exception from a context. On Python 3, this is equivalent to `raise exc_value from exc_value_from`. On Python 2, which does not support exception chaining, it is equivalent to `raise exc_value`.

six.reraise(exc_type, exc_value, exc_traceback=None)

  Reraise an exception, possibly with a different traceback. In the simple case, `reraise(*sys.exc_info())` with an active exception (in an except block) reraises the current exception with the last traceback. A different traceback can be specified with the exc_traceback parameter. Note that since the exception reraising is done within the `reraise()` function, Python will attach the call frame of `reraise()` to whatever traceback is raised.

six.with_metaclass(metaclass, *bases)

  Create a new class with base classes bases and metaclass metaclass. This is designed to be used in class declarations like this:

      from six import with_metaclass

      class Meta(type):
          pass

      class Base(object):
          pass

      class MyClass(with_metaclass(Meta, Base)):
          pass

  Another way to set a metaclass on a class is with the `add_metaclass()` decorator.

@six.add_metaclass(metaclass)

  Class decorator that replaces a normally-constructed class with a metaclass-constructed one. Example usage:

      @add_metaclass(Meta)
      class MyClass(object):
          pass

  That code produces a class equivalent to

      class MyClass(object, metaclass=Meta):
          pass

  on Python 3 or

      class MyClass(object):
          __metaclass__ = Meta

  on Python 2.

  Note that class decorators require Python 2.6. However, the effect of the decorator can be emulated on Python 2.5 like so:

      class MyClass(object):
          pass
      MyClass = add_metaclass(Meta)(MyClass)

### Binary and text data

Python 3 enforces the distinction between byte strings and text strings far more rigorously than Python 2 does; binary data cannot be automatically coerced to or from text data. six provides several functions to assist in classifying string data in all Python versions.

six.b(data)

  A “fake” bytes literal. data should always be a normal string literal. In Python 2, `b()` returns an 8-bit string. In Python 3, data is encoded with the latin-1 encoding to bytes.

  Note

  Since all Python versions 2.6 and after support the `b` prefix, code without 2.5 support doesn’t need `b()`.

six.u(text)

  A “fake” unicode literal. text should always be a normal string literal. In Python 2, `u()` returns unicode, and in Python 3, a string. Also, in Python 2, the string is decoded with the `unicode-escape` codec, which allows unicode escapes to be used in it.

  Note

  In Python 3.3, the `u` prefix has been reintroduced. Code that only supports Python 3 versions of 3.3 and higher thus does not need `u()`.

  Note

  On Python 2, `u()` doesn’t know what the encoding of the literal is. Each byte is converted directly to the unicode codepoint of the same value. Because of this, it’s only safe to use `u()` with strings of ASCII data.

six.unichr(c)

  Return the (Unicode) string representing the codepoint c. This is equivalent to `py2:unichr()` on Python 2 and `py3:chr()` on Python 3.

six.int2byte(i)

  Converts i to a byte. i must be in `range(0, 256)`. This is equivalent to `py2:chr()` in Python 2 and `bytes((i,))` in Python 3.

six.byte2int(bs)

  Converts the first byte of bs to an integer. This is equivalent to `ord(bs[0])` on Python 2 and `bs[0]` on Python 3.

six.indexbytes(buf, i)

  Return the byte at index i of buf as an integer. This is equivalent to indexing a bytes object in Python 3.

six.iterbytes(buf)

  Return an iterator over bytes in buf as integers. This is equivalent to a bytes object iterator in Python 3.

six.ensure_binary(s, encoding='utf-8', errors='strict')

  Coerce s to `binary_type`. encoding, errors are the same as `py3:str.encode()`

six.ensure_str(s, encoding='utf-8', errors='strict')

  Coerce s to `str`. encoding, errors are the same as `py3:str.encode()`

six.ensure_text(s, encoding='utf-8', errors='strict')

  Coerce s to `text_type`. encoding, errors are the same as `py3:bytes.decode()`

six.StringIO

  This is a fake file object for textual data. It’s an alias for `py2:StringIO.StringIO` in Python 2 and `py3:io.StringIO` in Python 3.

six.BytesIO

  This is a fake file object for binary data. In Python 2, it’s an alias for `py2:StringIO.StringIO`, but in Python 3, it’s an alias for `py3:io.BytesIO`.

@six.python_2_unicode_compatible

  A class decorator that takes a class defining a `__str__` method. On Python 3, the decorator does nothing. On Python 2, it aliases the `__str__` method to `__unicode__` and creates a new `__str__` method that returns the result of `__unicode__()` encoded with UTF-8.

### unittest assertions

Six contains compatibility shims for unittest assertions that have been renamed. The parameters are the same as their aliases, but you must pass the test method as the first argument. For example:

    import six
    import unittest

    class TestAssertCountEqual(unittest.TestCase):
        def test(self):
            six.assertCountEqual(self, (1, 2), [2, 1])

Note these functions are only available on Python 2.7 or later.

six.assertCountEqual()

  Alias for `assertCountEqual()` on Python 3 and `assertItemsEqual()` on Python 2.

six.assertRaisesRegex()

  Alias for `assertRaisesRegex()` on Python 3 and `assertRaisesRegexp()` on Python 2.

six.assertRegex()

  Alias for `assertRegex()` on Python 3 and `assertRegexpMatches()` on Python 2.

six.assertNotRegex()

  Alias for `assertNotRegex()` on Python 3 and `assertNotRegexpMatches()` on Python 2.

### Renamed modules and attributes compatibility

Python 3 reorganized the standard library and moved several functions to different modules. Six provides a consistent interface to them through the fake `six.moves` module. For example, to load the module for parsing HTML on Python 2 or 3, write:

    from six.moves import html_parser

Similarly, to get the function to reload modules, which was moved from the builtin module to the `importlib` module, use:

    from six.moves import reload_module

For the most part, `six.moves` aliases are the names of the modules in Python 3. When the new Python 3 name is a package, the components of the name are separated by underscores. For example, `html.parser` becomes `html_parser`. In some cases where several modules have been combined, the Python 2 name is retained. This is so the appropriate modules can be found when running on Python 2. For example, `BaseHTTPServer` which is in `http.server` in Python 3 is aliased as `BaseHTTPServer`.

Some modules which had two implementations have been merged in Python 3. For example, `cPickle` no longer exists in Python 3; it was merged with `pickle`. In these cases, fetching the fast version will load the fast one on Python 2 and the merged module in Python 3.

The `py2:urllib`, `py2:urllib2`, and `py2:urlparse` modules have been combined in the `py3:urllib` package in Python 3. The `six.moves.urllib` package is a version-independent location for this functionality; its structure mimics the structure of the Python 3 `py3:urllib` package.

Note

In order to make imports of the form:

    from six.moves.cPickle import loads

work, six places special proxy objects in `py3:sys.modules`. These proxies lazily load the underlying module when an attribute is fetched. This will fail if the underlying module is not available in the Python interpreter. For example, `sys.modules["six.moves.winreg"].LoadKey` would fail on any non-Windows platform. Unfortunately, some applications try to load attributes on every module in `py3:sys.modules`. six mitigates this problem for some applications by pretending attributes on unimportable modules do not exist. This hack does not work in every case, though. If you are encountering problems with the lazy modules and don’t use any from imports directly from `six.moves` modules, you can workaround the issue by removing the six proxy modules:

    d = [name for name in sys.modules if name.startswith("six.moves.")]
    for name in d:
        del sys.modules[name]

Supported renames:

Name | Python 2 name | Python 3 name
--- | --- | ---
`builtins` | `py2:__builtin__` | `py3:builtins`
`configparser` | `py2:ConfigParser` | `py3:configparser`
`copyreg` | `py2:copy_reg` | `py3:copyreg`
`cPickle` | `py2:cPickle` | `py3:pickle`
`cStringIO` | `py2:cStringIO.StringIO()` | `py3:io.StringIO`
`collections_abc` | `py2:collections` | `py3:collections.abc` (3.3+)
`dbm_gnu` | `py2:gdbm` | `py3:dbm.gnu`
`dbm_ndbm` | `py2:dbm` | `py3:dbm.ndbm`
`_dummy_thread` | `py2:dummy_thread` | `py3:_dummy_thread` (< 3.9) `py3:_thread` (3.9+)
`email_mime_base` | `py2:email.MIMEBase` | `py3:email.mime.base`
`email_mime_image` | `py2:email.MIMEImage` | `py3:email.mime.image`
`email_mime_multipart` | `py2:email.MIMEMultipart` | `py3:email.mime.multipart`
`email_mime_nonmultipart` | `py2:email.MIMENonMultipart` | `py3:email.mime.nonmultipart`
`email_mime_text` | `py2:email.MIMEText` | `py3:email.mime.text`
`filter` | `py2:itertools.ifilter()` | `py3:filter()`
`filterfalse` | `py2:itertools.ifilterfalse()` | `py3:itertools.filterfalse()`
`getcwd` | `py2:os.getcwdu()` | `py3:os.getcwd()`
`getcwdb` | `py2:os.getcwd()` | `py3:os.getcwdb()`
`getoutput` | `py2:commands.getoutput()` | `py3:subprocess.getoutput()`
`http_cookiejar` | `py2:cookielib` | `py3:http.cookiejar`
`http_cookies` | `py2:Cookie` | `py3:http.cookies`
`html_entities` | `py2:htmlentitydefs` | `py3:html.entities`
`html_parser` | `py2:HTMLParser` | `py3:html.parser`
`http_client` | `py2:httplib` | `py3:http.client`
`BaseHTTPServer` | `py2:BaseHTTPServer` | `py3:http.server`
`CGIHTTPServer` | `py2:CGIHTTPServer` | `py3:http.server`
`SimpleHTTPServer` | `py2:SimpleHTTPServer` | `py3:http.server`
`input` | `py2:raw_input()` | `py3:input()`
`intern` | `py2:intern()` | `py3:sys.intern()`
`map` | `py2:itertools.imap()` | `py3:map()`
`queue` | `py2:Queue` | `py3:queue`
`range` | `py2:xrange()` | `py3:range()`
`reduce` | `py2:reduce()` | `py3:functools.reduce()`
`reload_module` | `py2:reload()` | `py3:imp.reload()`, `py3:importlib.reload()` on Python 3.4+
`reprlib` | `py2:repr` | `py3:reprlib`
`shlex_quote` | `py2:pipes.quote` | `py3:shlex.quote`
`socketserver` | `py2:SocketServer` | `py3:socketserver`
`_thread` | `py2:thread` | `py3:_thread`
`tkinter` | `py2:Tkinter` | `py3:tkinter`
`tkinter_dialog` | `py2:Dialog` | `py3:tkinter.dialog`
`tkinter_filedialog` | `py2:FileDialog` | `py3:tkinter.FileDialog`
`tkinter_scrolledtext` | `py2:ScrolledText` | `py3:tkinter.scrolledtext`
`tkinter_simpledialog` | `py2:SimpleDialog` | `py3:tkinter.simpledialog`
`tkinter_ttk` | `py2:ttk` | `py3:tkinter.ttk`
`tkinter_tix` | `py2:Tix` | `py3:tkinter.tix`
`tkinter_constants` | `py2:Tkconstants` | `py3:tkinter.constants`
`tkinter_dnd` | `py2:Tkdnd` | `py3:tkinter.dnd`
`tkinter_colorchooser` | `py2:tkColorChooser` | `py3:tkinter.colorchooser`
`tkinter_commondialog` | `py2:tkCommonDialog` | `py3:tkinter.commondialog`
`tkinter_tkfiledialog` | `py2:tkFileDialog` | `py3:tkinter.filedialog`
`tkinter_font` | `py2:tkFont` | `py3:tkinter.font`
`tkinter_messagebox` | `py2:tkMessageBox` | `py3:tkinter.messagebox`
`tkinter_tksimpledialog` | `py2:tkSimpleDialog` | `py3:tkinter.simpledialog`
`urllib.parse` | See `six.moves.urllib.parse` | `py3:urllib.parse`
`urllib.error` | See `six.moves.urllib.error` | `py3:urllib.error`
`urllib.request` | See `six.moves.urllib.request` | `py3:urllib.request`
`urllib.response` | See `six.moves.urllib.response` | `py3:urllib.response`
`urllib.robotparser` | `py2:robotparser` | `py3:urllib.robotparser`
`urllib_robotparser` | `py2:robotparser` | `py3:urllib.robotparser`
`UserDict` | `py2:UserDict.IterableUserDict` | `py3:collections.UserDict`
`UserList` | `py2:UserList.UserList` | `py3:collections.UserList`
`UserString` | `py2:UserString.UserString` | `py3:collections.UserString`
`winreg` | `py2:_winreg` | `py3:winreg`
`xmlrpc_client` | `py2:xmlrpclib` | `py3:xmlrpc.client`
`xmlrpc_server` | `py2:SimpleXMLRPCServer` | `py3:xmlrpc.server`
`xrange` | `py2:xrange()` | `py3:range()`
`zip` | `py2:itertools.izip()` | `py3:zip()`
`zip_longest` | `py2:itertools.izip_longest()` | `py3:itertools.zip_longest()`

#### urllib parse

Contains functions from Python 3’s `py3:urllib.parse` and Python 2’s:

`py2:urlparse`:

- `py2:urlparse.ParseResult()`

- `py2:urlparse.SplitResult()`

- `py2:urlparse.urlparse()`

- `py2:urlparse.urlunparse()`

- `py2:urlparse.parse_qs()`

- `py2:urlparse.parse_qsl()`

- `py2:urlparse.urljoin()`

- `py2:urlparse.urldefrag()`

- `py2:urlparse.urlsplit()`

- `py2:urlparse.urlunsplit()`

- `py2:urlparse.splitquery()`

- `py2:urlparse.uses_fragment()`

- `py2:urlparse.uses_netloc()`

- `py2:urlparse.uses_params()`

- `py2:urlparse.uses_query()`

- `py2:urlparse.uses_relative()`

and `py2:urllib`:

- `py2:urllib.quote()`

- `py2:urllib.quote_plus()`

- `py2:urllib.splittag()`

- `py2:urllib.splituser()`

- `py2:urllib.splitvalue()`

- `py2:urllib.unquote()` (also exposed as `py3:urllib.parse.unquote_to_bytes()`)

- `py2:urllib.unquote_plus()`

- `py2:urllib.urlencode()`

#### urllib error

Contains exceptions from Python 3’s `py3:urllib.error` and Python 2’s:

`py2:urllib`:

- `py2:urllib.ContentTooShortError`

and `py2:urllib2`:

- `py2:urllib2.URLError`

- `py2:urllib2.HTTPError`

#### urllib request

Contains items from Python 3’s `py3:urllib.request` and Python 2’s:

`py2:urllib`:

- `py2:urllib.pathname2url()`

- `py2:urllib.url2pathname()`

- `py2:urllib.getproxies()`

- `py2:urllib.urlretrieve()`

- `py2:urllib.urlcleanup()`

- `py2:urllib.URLopener`

- `py2:urllib.FancyURLopener`

- `py2:urllib.proxy_bypass()`

and `py2:urllib2`:

- `py2:urllib2.urlopen()`

- `py2:urllib2.install_opener()`

- `py2:urllib2.build_opener()`

- `py2:urllib2.parse_http_list()`

- `py2:urllib2.parse_keqv_list()`

- `py2:urllib2.Request`

- `py2:urllib2.OpenerDirector`

- `py2:urllib2.HTTPDefaultErrorHandler`

- `py2:urllib2.HTTPRedirectHandler`

- `py2:urllib2.HTTPCookieProcessor`

- `py2:urllib2.ProxyHandler`

- `py2:urllib2.BaseHandler`

- `py2:urllib2.HTTPPasswordMgr`

- `py2:urllib2.HTTPPasswordMgrWithDefaultRealm`

- `py2:urllib2.AbstractBasicAuthHandler`

- `py2:urllib2.HTTPBasicAuthHandler`

- `py2:urllib2.ProxyBasicAuthHandler`

- `py2:urllib2.AbstractDigestAuthHandler`

- `py2:urllib2.HTTPDigestAuthHandler`

- `py2:urllib2.ProxyDigestAuthHandler`

- `py2:urllib2.HTTPHandler`

- `py2:urllib2.HTTPSHandler`

- `py2:urllib2.FileHandler`

- `py2:urllib2.FTPHandler`

- `py2:urllib2.CacheFTPHandler`

- `py2:urllib2.UnknownHandler`

- `py2:urllib2.HTTPErrorProcessor`

#### urllib response

Contains classes from Python 3’s `py3:urllib.response` and Python 2’s:

`py2:urllib`:

- `py2:urllib.addbase`

- `py2:urllib.addclosehook`

- `py2:urllib.addinfo`

- `py2:urllib.addinfourl`

#### Advanced - Customizing renames

It is possible to add additional names to the `six.moves` namespace.

six.add_move(item)

  Add item to the `six.moves` mapping. item should be a `MovedAttribute` or `MovedModule` instance.

six.remove_move(name)

  Remove the `six.moves` mapping called name. name should be a string.

Instances of the following classes can be passed to `add_move()`. Neither have any public members.

class six.MovedModule(name, old_mod, new_mod)

  Create a mapping for `six.moves` called name that references different modules in Python 2 and 3. old_mod is the name of the Python 2 module. new_mod is the name of the Python 3 module.

class six.MovedAttribute(name, old_mod, new_mod, old_attr=None, new_attr=None)

  Create a mapping for `six.moves` called name that references different attributes in Python 2 and 3. old_mod is the name of the Python 2 module. new_mod is the name of the Python 3 module. If new_attr is not given, it defaults to old_attr. If neither is given, they both default to name.