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I have read probably all of the posts on here regarding imports and I still cannot figure out what is going on with the imports, I have spent hours trying to get a very simple example working and am literally pulling my hair out.

I am using python 3.7 and pycharm but I am running my code from the commandline, for the unit tests I am using pytest.

My project structure is:

my_message_validator/ __init__.py module_1/ __init.py__ foo.py module_2/ __init.py__ bar.py baz.py module_3 context.py test_all.py

module_1.init.py

from module_1 import foo

module_2.init.py

# For some reason pycharm doesnt complain when I use '.' but if I use module_2 it does from . import bar, baz

If I try to run my code or my tests from the commandline no matter how I move things around I seem to get either ModuleNotFoundError: No module named, when I have managed to get the tests working I still cannot run my code on its own from the commandline.

How can I import module_1 into module_2 and are these actually packages? I am coming from java and find the imports a lot easier to understand, I am finding the python importing very confusing...

Also how can I can then import whatever I need into my test module\package\folders context.py?

Currently the test context look like:

import os import sys # Is this needed as it doesnt seem to do anything? sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))) from module_1.foo import Foo from module_2 import bar, baz

In test_all.py I am trying to import from the context file like this:

from .context import bar,baz from .context import Foo # Calling in test like Foo.load_file(file) bar.method_one() baz.method_two()

Do I need all the __init.py__ files and what should I be putting in them to make my methods and classes public\exposed? I would like this entire package to be reusable so want to be able to treat it like a jar file in java.

Any help would be much appreciated as it seems everytime I change something I get an error in a different place, python seems so much more complicated than java right now.

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  • Have you tried importing like: from my_message_validator.module_1.foo import Foo ? Commented Nov 14, 2019 at 23:59

3 Answers 3

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First, do not use relative imports (with .), as it is known for causing multiple issues. Always write your imports relative to the root of your project. For example, you did it well for from module_1.foo import Foo. You should also do it in test_all.py and context.py. Moreover, after using relative imports, the __init__.py files can be left empty in your case.

Most likely, the Python interpreter cannot find your modules because the PYTHONPATH environment variable does not contain the root of your project. If you run export PYTHONPATH="YOUR_PROJECT_ROOT_ABSOLUTE_PATH:$PYTHONPATH" before your script, it should run as expected. To make sure this variable is set all the time, you can add the export statement to your shell profile file (e.g. .bashrc or .bash_profile).

After chatting with the author, it turns out there was a fourth issue. It was a name collision like the one in this other question. In his project directory, module_1 was actually called foo like its child foo.py, which confused the interpreter.

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9 Comments

So would you suggest I get rid of all of the __init__.py files? If bar and baz only contain functions and not classes what is the correct way to import them?
Yes indeed, I suggest you delete all __init__.py files. Regarding bar and baz, you can import functions from them similarly to how you import classes in Java. That is, you can do from module_2.bar import my_bar_function and from module_2.baz import my_baz_function. Then, you can simply call my_bar_function() and my_baz_function() in your script.
And is there any point in using a context.py for the tests? I followed a tutorial on how to create packages and it seems to be handling the imports for test suites which then import from .context
It generally depends on how much code is shared between your different tests. I would suggest you start the project without context.py, and then add it later in case you find yourself importing the same things all the time across your different tests.
@djvg Thanks for the comment. I agree, and would add that some linters or static analysis tools won't explore directories that are not regular packages. I edited the answer.
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Have you tried importing like: 

from my_message_validator.module_1.foo import Foo from my_message_validator.module_2 import bar, baz
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I had thought that using the __init__.py files and then exporting there (using import) would mean I wouldnt have to give the full path to everything. What is the norm when developing with python?
If I would use the absolute path over relative paths do I need to bother with __init__.py files at all?
When I have added the absolute path to my unit test then I get this error instead ModuleNotFoundError: No module named 'my_message_validator' although pycharm seems to be happy with this format
absolute path for import is required as Python is recognizing your project path by root directory. Rest of the modules you'll require to mention root onwards.
Rest of the modules you'll require to mention root onwards, could you update your answer with an example please, I dont know what you mean.
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I had the same case.
I started the application in this way: 

flask run

And every time I got a ModuleNotFoundError error on the website.
When I started the application like this: 

python3 -m flask run

the application started without errors :-) .

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