Python – Does Import Order Matter

python

I read here about sorting your import statements in Python, but what if the thing you are importing needs dependencies that have not been imported yet? Is this the difference between compiled languages and interpreted? I come from a JavaScript background and the order in which you load your scripts matter, whereas Python appears not to care. Thanks.

Best Answer

Import order does not matter. If a module relies on other modules, it needs to import them itself. Python treats each .py file as a self-contained unit as far as what's visible in that file.

_{(Technically, changing import order could change behavior, because modules can have initialization code that runs when they are first imported. If that initialization code has side effects it's possible for modules to have interactions with each other. However, this would be a design flaw in those modules. Import order is not supposed to matter, so initialization code should also be written to not depend on any particular ordering.)}

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Python Paths and Import Order Explained

Python searches the paths in sys.path in order (see http://docs.python.org/tutorial/modules.html#the-module-search-path). easy_install changes this list directly (see the last line in your easy-install.pth file):

import sys; new=sys.path[sys.__plen:]; del sys.path[sys.__plen:]; p=getattr(sys,'__egginsert',0); sys.path[p:p]=new; sys.__egginsert = p+len(new)

This basically takes whatever directories are added and inserts them at the beginning of the list.

Also see Eggs in path before PYTHONPATH environment variable.

Python Import – Order of Import for Modules Explained

I'm not sure where (or whether) this information is in the documentation - a quick check in the import system docs didn't turn it up - but PEP 420 says the following:

While looking for a module or package named "foo", for each directory in the parent path:

If <directory>/foo/__init__.py is found, a regular package is imported and returned.

If not, but <directory>/foo.{py,pyc,so,pyd} is found, a module is imported and returned. The exact list of extension varies by platform and whether the -O flag is specified. The list here is representative.

If not, but <directory>/foo is found and is a directory, it is recorded and the scan continues with the next directory in the parent path.

Otherwise the scan continues with the next directory in the parent path.

If the scan completes without returning a module or package, and at least one directory was recorded, then a namespace package is created.

So according to PEP 420, if a package and a non-package module are found in the same directory with the same name, the package wins.

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Python Paths and Import Order Explained

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