from … import OR import … as for modules

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Question :

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 and there is no need/wish for changing the name (bar)?

Are there any differences? Does it matter?

Asked By: embert

||

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

* 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.

Answered By: Martijn Pieters

Answer #2:

This is a late answer, arising from what is the difference between ‘import a.b as b’ and ‘from a import b’ in python

This question has been flagged as a duplicate, but there is an important difference between the two mechanisms that has not been addressed by others.

from foo import bar imports any object called bar from namespace foo into the current namespace.

import foo.bar as bar imports an importable object (package/module/namespace) called foo.bar and gives it the alias bar.

What’s the difference?

Take a directory (package) called foo which has an __init__.py containing:

# foo.__init__.py
class myclass:
    def __init__(self, var):
        self.__var = var

    def __str__(self):
        return str(self.__var)

bar = myclass(42)

Meanwhile, there is also a module in foo called bar.py.

from foo import bar
print(bar)

Gives:

42

Whereas:

import  foo.bar as bar
print(bar)

Gives:

<module 'foo.bar' from '/Users//..../foo/bar.py'>

So it can be seen that import foo.bar as bar is safer.

Answered By: cdarke

Answer #3:

You can use as to rename modules suppose you have two apps that have views and you want to import them

from app1 import views as views1
from app2 import views as views2

if you want multiple import use comma separation

>>> from datetime import date as d, time as t
>>> d
<type 'datetime.date'>
>>> t
<type 'datetime.time'>
Answered By: A.Zaben

Answer #4:

Both are technically different:

  • import torch.nn as nn will only import a module/package torch.nn, wheres
  • from torch import nn can and will prefer to import an attribute .nn from the torch module/package. Importing a module/package torch.nn is a fall.back.

In practice, it is bad style to have the same fully qualified name refer to two separate things. As such, torch.nn should only refer to a module/package. In this common case, both import statements are functionally equivalent: The same object is imported and bound to the same name.

Which one to choose comes down to preference if the target always is a module. There are practical differences when refactoring:

  • import torch.nn as nn guarantees .nn is a module/package. It protects against accidentally shadowing with an attribute.
  • from torch import nn does not care what .nn is. It allows to transparently change the implementation.

7.11. The import statement

The basic import statement (no from clause) is executed in two steps:

  1. find a module, loading and initializing it if necessary
  2. define a name or names in the local namespace for the
    scope where the import statement occurs.

[…]

The from form uses a slightly more complex process:

  1. find the module specified in the from clause, loading and initializing it if necessary;

  2. for each of the identifiers specified in the import clauses:

    1. check if the imported module has an attribute by that name
    2. if not, attempt to import a submodule with that name and then check the imported module again for that attribute
Answered By: MisterMiyagi

Answer #5:

The only thing I can see for the second option is that you will need as many lines as things you want to import. For example :

import foo.bar as bar
import foo.tar as tar
import foo.zar as zar

Instead of simply doing :

from foo import bar, tar, zar
Answered By: Depado

Answer #6:

The difference between import module and from module import is mainly subjective. Pick the one you like best and be consistent in your use of it. Here are some advantage of both to help you decide.

advantage of import

  1. Less maintenance of your import statements.
  2. Don’t need to add any additional imports to start using another item from the module

advantage of from torch import nn

  1. Less typing to use the nn
  2. More control over which items of a module can be accessed
Answered By: Prathamesh Jadhav

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