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Suppose I have a module rules with the following structure:

rules
├── conditions.py
├── __init__.py

In the script conditions.py, I'd like to import a class called RuleParserError defined in __init__.py. However, I haven't been able to figure out how to do this. (Following Python: How to import from an __init__.py file? I've tried

from . import RuleParserError

but this leads to an ImportError: cannot import name RuleParserError when trying to run conditions.py as __main__).

Sabito stands with Ukraine
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Kurt Peek
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3 Answers3

31

I see 'import from parent module' as an anti-pattern in Python. Imports should be the other way around. Importing from modules's __init__.py is especially problematic. As you noticed, importing module foo.bar from foo/bar.py involves importing foo/__init__.py first, and you may end up with a circular dependency. Adding a print("Importing", __name__) to your init files helps see the sequence and understand the problem.

I'd suggest that you moved the code you want to import in conditions.py from __init__.py to a separate lower-level module, and just import some names from that module in __init__.py to expose it at higher level.

Let's suppose that you had some class Bar in your __init__.py. I'd reorganize it the following way.

__init__.py:

from bar import Bar  # exposed at the higher level, as it used to be.

bar.py:

class Bar(object): ...

conditions.py:

from . import Bar  # Now it works.

Ideally an __init__.py should contain nothing but imports from lower-level modules, or nothing at all.

9000
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  • Can you include a directory tree showing where the files are in your example? I have tried several arrangements that seem to match what you describe, yet I get errors at every attempt, including "cannot import from partially initialized module," "no module named x," "attempted relative import with no known parent package," "cannot import name X from x (unknown location)." – user513951 Mar 30 '23 at 13:13
9

If you get

ImportError: attempted relative import with no known parent package

when you do like

import . from something

especially from the script executed, just try

from __init__ import something

Even though it could be problematic when there are many __init__.pys in sys.path, it would be helpful in some simple situaions.

ghchoi
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0

adding __package__ on top the script

__package__ = "pkg.dir.dir"

resolving the issue

in this case

__package__ = "rules"
muTheTechie
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