Previously, and now currently, packages in Python have been a source of much woe to me. Plagued by hundred of “No module named xxx”, “Attempted relative import in non-package” etc, it is now time to write myself a little guide to refer to in future.
A package is a collection of modules with a __init__.py file inside the
package directory and a module is simply a python file.
Say I have the layout:
* core:
* __init__.py
* queue.py
* tests:
* queue_tests.py
and I want the Queue class from core.queue. How do I import this in
queue_tests.py?
You’d think
from ..queue import Queue
def blah():
stuff()would do it; and you’d be correct. But check how you’re running the file. If
you’re running it directly like python tests/queue_tests.py, then the name of the file will
be __main__ which breaks relative imports. You have to run it like so: python
-m tests.queue_tests. This runs the module queue_tests as a script, but fixes
the __name__ issue.