How to add custom renames in six?

Question

According to the documentation, six supports adding custom renames to six.moves:

six.add_move(item)

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

And:

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.

However, this code yields an ImportError for me:

from six import add_move, MovedModule
add_move(MovedModule('mock', 'mock', 'unittest.mock'))
from six.moves.mock import MagicMock

When I run it on Python 3.4.2 using six 1.9.0 I get this error:

Traceback (most recent call last):
  File "test_six_moves.py", line 2, in <module>
    from six.moves.mock import MagicMock
ImportError: No module named 'six.moves.mock'

The builtin moves are working just fine. How do I get this to work?

Answer 1

You can't import the name from within the move. Use:

from __future__ import print_function

from six import add_move, MovedModule
add_move(MovedModule('mock', 'mock', 'unittest.mock'))

from six.moves import mock
print(mock.MagicMock)

This will give you:

# Python 2
<class 'mock.MagicMock'>

# Python 3
<class 'unittest.mock.MagicMock'>

---

Note that importing from within a move works for the ones that ship with six. For example: from six.moves.configparser import ConfigParser works.

This piece of code (from six.py) is why:

for attr in _moved_attributes:
    setattr(_MovedItems, attr.name, attr)
    if isinstance(attr, MovedModule):
        _importer._add_module(attr, "moves." + attr.name)

In fact, if you ran the following (meddling with private attributes is of course not recommended), your import would work:

import six
mod = six.MovedModule('mock', 'mock', 'unittest.mock')
six.add_move(mod)
six._importer._add_module(mod, "moves." + mod.name)