Is using __import__('module_name') an antipattern in Python?

Question

I'm currently refactoring a Python 2 project which includes the ability to add or remove plugins, which are Python modules implementing a given API.

The main app accesses add/remove/update hooks in plugins by calling e.g. __import__('plugin_name').hook_add() after pulling plugin names from a database, but this seems like a hacky approach. Having said that, I don't know of better ways to programatically access plugins.

Is this considered an antipattern in Python?

Answer 1

Is using __import__('module_name') an antipattern in Python?

The api for __import__ is somewhat misleading. I personally would prefer to avoid it where possible.

The docs for Python 3 state:

Direct use of __import__() is also discouraged in favor of importlib.import_module().

Here's the API for __import__:

mod = __import__(
    module, # string of dotted name
    globals=None, # only needed to do relative import
    locals=None, # implementation ignores this
    fromlist=()) # fromlist just needs to be non-empty... :(
    level=0 # relative import, not going into this part
    )

If fromlist is empty, you import the module, but get returned the root package like this, so you have to do the dotted lookup to get back to it:

>>> foo = __import__('foo.bar.baz')
>>> foo.bar.baz
<module 'foo.bar.baz' from /.../foo/bar/baz.py>

This is the same as

>>> import foo.bar.baz
>>> foo.bar.baz
<module 'foo.bar.baz' from /.../foo/bar/baz.py>

If you just want the module, you need fromlist to be non-empty:

>>> baz = __import__('foo.bar.baz', fromlist=[None])
>>> baz
<module 'foo.bar.baz' from /.../foo/bar/baz.py>

Which is the same as

>>> from foo.bar import baz
>>> baz
<module 'foo.bar.baz' from /.../foo/bar/baz.py>

>>> baz is foo.bar.baz
True

Use importlib.import_module instead:

Here's the usage for import_module:

>>> from importlib import import_module
>>> baz = import_module('foo.bar.baz')

That's much nicer.