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__).
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.
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.
adding __package__ on top the script
__package__ = "pkg.dir.dir"
resolving the issue
in this case
__package__ = "rules"
