CODEWITHSUNDEEP
python
Chris Matta
Chris Matta

Reputation: 3433

Does the python sys.path act like Unix PATH?

Let's say I have a local development directory with modules that I'm writing, and a system-wide site-packages directory where these modules will eventually be installed. In the case where I'm modifying an existing module and I want to test it I would like to be sure that the module I'm importing is the one in my local site-packages directory. Reading about the site module it seems like I can have a file with a .pth suffix where each line in that file will be appended to the sys.path variable. I've set that up, and I can confirm that my development directory is showing up later in the list, but when I import a module it's importing from the system wide directory.

Simplified Example:

$ virtualenv test_sys
$ cd test_sys
$ source bin/activate
$ mkdir site_modules
$ mkdir user_modules

In each site_modules and user_modules I've put a directory called test_module with the following in the __init__.py:

import os

print(os.path.abspath(__file__))

Now I've added a file called site_modules.pth to test_sys/lib/python2.7/site-packages:

/home/chris/test_sys/site_modules
/home/chris/test_sys/user_modules

And I expect that when I import test_module from the python interpreter it would print the user_modules directory but it doesn't:

>>> import test_module
/home/chris/test_sys/site_modules/test_module/__init__.pyc
>>>

Yes, I've ensured that user_modules shows up later in sys.path than site_modules.

How can I ensure that a module that exists in multiple directories in sys.path will always be imported from a specific directory?

Upvotes: 0

Views: 131

Answers (1)

Dietrich Epp
Dietrich Epp

Reputation: 213688

Python's sys.path does work mostly like the Unix PATH environment variable. Both of them use the first object they find in the path. So if you want to have user_modules override site_modules, you have to put it first, not second:

/home/chris/test_sys/user_modules
/home/chris/test_sys/site_modules

This is the same as Unix PATH

PATH=/usr/local/bin:/usr/bin:/bin

Which means that local packages (ones not installed by the package manager) from /usr/local will override system packages in /usr.

Upvotes: 1

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