Relative imports - ModuleNotFoundError: No module

问题:

This is the first time I've really sat down and tried python 3, and seem to be failing miserably. I have the following two files:

1. test.py
2. config.py

config.py has a few functions defined in it as well as a few variables. I've stripped it down to the following:

However, I'm getting the following error:

ModuleNotFoundError: No module named 'config'

I'm aware that the py3 convention is to use absolute imports:

from . import config

However, this leads to the following error:

ImportError: cannot import name 'config'

So I'm at a loss as to what to do here... Any help is greatly appreciated. :)

回答1:

TL;DR: you can't do relative imports from the file you execute since __main__ module is not a part of a package.

Absolute imports - import something available on sys.path

Relative imports - import something relative to the current module, must be a part of a package

If you're running both variants in exactly the same way, one of them should work. Anyway, here is an example that should help you understand what's going on, let's add another main.py file with the overall directory structure like this:

.
./main.py
./ryan/__init__.py
./ryan/config.py
./ryan/test.py

And let's update test.py to see what's going on:

# config.py
debug = True


# test.py
print(__name__)

try:
    # Trying to find module in the parent package
    from . import config
    print(config.debug)
    del config
except ImportError:
    print('Relative import failed')

try:
    # Trying to find module on sys.path
    import config
    print(config.debug)
except ModuleNotFoundError:
    print('Absolute import failed')


# main.py
import ryan.test

Let's run test.py first:

$ python ryan/test.py
__main__
Relative import failed
True

Here "test" is the __main__ module and doesn't know anything about belonging to a package. However import config should work, since the ryan folder will be added to sys.path.

Let's run main.py instead:

$ python main.py
ryan.test
True
Absolute import failed

And here test is inside of the "ryan" package and can perform relative imports. import config fails since implicit relative imports are not allowed in Python 3.

Hope this helped.

P.S.: if you're sticking with Python 3 there is no more need in __init__.py files.

回答2:

I figured it out. Very frustrating, especially coming from python2.

You have to add a . to the module, regardless of whether or not it is relative or absolute.

I created the directory setup as follows.

/main.py
--/lib
  --/__init__.py
  --/mody.py
  --/modx.py

modx.py

def does_something():
    return "I gave you this string."

mody.py

from modx import does_something

def loaded():
    string = does_something()
    print(string)

main.py

from lib import mody

mody.loaded()

when I execute main, this is what happens

$ python main.py
Traceback (most recent call last):
  File "main.py", line 2, in <module>
    from lib import mody
  File "/mnt/c/Users/Austin/Dropbox/Source/Python/virtualenviron/mock/package/lib/mody.py", line 1, in <module>
    from modx import does_something
ImportError: No module named 'modx'

I ran 2to3, and the core output was this

RefactoringTool: Refactored lib/mody.py
--- lib/mody.py (original)
+++ lib/mody.py (refactored)
@@ -1,4 +1,4 @@
-from modx import does_something
+from .modx import does_something

 def loaded():
     string = does_something()
RefactoringTool: Files that need to be modified:
RefactoringTool: lib/modx.py
RefactoringTool: lib/mody.py

I had to modify mody.py's import statement to fix it

try:
    from modx import does_something
except ImportError:
    from .modx import does_something


def loaded():
    string = does_something()
    print(string)

Then I ran main.py again and got the expected output

$ python main.py
I gave you this string.

Lastly, just to clean it up and make it portable between 2 and 3.

from __future__ import absolute_import
from .modx import does_something

回答3:

Setting PYTHONPATH can also help with this problem.

Here is how it can be done on Windows

set PYTHONPATH=.

回答4:

You have to append the module’s path to PYTHONPATH:

export PYTHONPATH="${PYTHONPATH}:/path/to/your/module/"

回答5:

Tried your example

from . import config

got the following SystemError:
/usr/bin/python3.4 test.py
Traceback (most recent call last):
File "test.py", line 1, in
from . import config
SystemError: Parent module '' not loaded, cannot perform relative import

---

This will work for me:

import config
print('debug=%s'%config.debug)

>>>debug=True

Tested with Python:3.4.2 - PyCharm 2016.3.2

---

Beside this PyCharm offers you to Import this name.
You hav to click on config and a help icon appears.

回答6:

You can simply add following file to your tests directory, and then python will run it before the tests

__init__.py file

import os
import sys
sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))

回答7:

This example works on Python 3.6.

I suggest going to Run -> Edit Configurations in PyCharm, deleting any entries there, and trying to run the code through PyCharm again.

If that doesn't work, check your project interpreter (Settings -> Project Interpreter) and run configuration defaults (Run -> Edit Configurations...).

回答8:

Declare correct sys.path list before you call module:

import os, sys

#'/home/user/example/parent/child'
current_path = os.path.abspath('.')

#'/home/user/example/parent'
parent_path = os.path.dirname(current_path)

sys.path.append(parent_path)
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'child.settings')

回答9:

As was stated in the comments to the original post, this seemed to be an issue with the python interpreter I was using for whatever reason, and not something wrong with the python scripts. I switched over from the WinPython bundle to the official python 3.6 from python.org and it worked just fine. thanks for the help everyone :)