pythonimportmodule

from ... import OR import ... as for modules

Should I use

from foo import bar

OR

import foo.bar as bar

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

Are there any differences? Does it matter?

Solution

  • 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

    Note that if bar is both a module inside foo and an object in the foo package namespace (so imported into the __init__.py module or defined there), then from foo import bar will import the object, and import foo.bar as bar imports the module.

    * 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.