python - from ... import OR import ... as for modules

Question

Should I use

from foo import bar

OR

import foo.bar as bar

when importing a module and and there is no need/wish for changing the name (bar)?

Are there any differences? Does it matter?

Answer 1

Assuming that bar is a module or package in foo, there is no difference^*, it doesn't matter. The two statements have exactly the same result:

>>> import os.path as path
>>> path
<module 'posixpath' from '/Users/mj/Development/venvs/stackoverflow-2.7/lib/python2.7/posixpath.pyc'>
>>> from os import path
>>> path
<module 'posixpath' from '/Users/mj/Development/venvs/stackoverflow-2.7/lib/python2.7/posixpath.pyc'>

If bar is not a module or package, the second form will not work; a traceback is thrown instead:

>>> import os.walk as walk
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named walk

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^* In Python 3.6 and before, there was a bug with the initialization ordering of packages containing other modules, where in the loading stage of the package using import contained.module.something as alias in a submodule would fail where from contained.module import something as alias would not. See Imports in __init__.py and `import as` statement for a very illustrative example of that problem, as well as Python issues #23203 and #30024.