ImportError: No module named - Python

问题:

I have a python application with the following directory structure:

src
 |
 +---- main
 |
 +---- util
 |
 +---- gen_py
         |
         +---- lib

In the package main, I have a python module named MyServer.py which has an import statement like:

from gen_py.lib import MyService

In order for this statement to work, I placed the following line at the beginning of MyServer.py:

import sys
sys.path.append('../gen_py/lib')

When I run MyServer.py in the terminal, I get the following error:

ImportError: No module named gen_py.lib

What I am missing here?

回答1:

Your modification of sys.path assumes the current working directory is always in main/. This is not the case. Instead, just add the parent directory to sys.path:

import sys
import os.path

sys.path.append(os.path.join(os.path.dirname(__file__), '..'))
import gen_py.lib

Don't forget to include a file __init__.py in gen_py and lib - otherwise, they won't be recognized as Python modules.

回答2:

For the Python module import to work, you must have "src" in your path, not "gen_py/lib".

When processing an import like import gen_py.lib, it looks for a module gen_py, then looks for a submodule lib.

As the module gen_py won't be in "../gen_py/lib" (it'll be in ".."), the path you added will do nothing to help the import process.

Depending on where you're running it from, try adding the relative path to the "src" folder. Perhaps it's sys.path.append('..'). You might also have success running the script while inside the src folder directly, via relative paths like python main/MyServer.py

回答3:

from ..gen_py.lib import MyService

or

from main.gen_py.lib import MyService

Make sure you have a (at least empty) __init__.py file on each directory.

回答4:

make sure to include __init__.py, which makes Python know that those directories containpackages

回答5:

This is if you are building a package and you are finding error in imports. I learnt it the hard way.The answer isn't to add the package to python path or to do it programatically (what if your module gets installed and your command adds it again?) thats a bad way.

The right thing to do is: 1) Use virtualenv pyvenv-3.4 or something similar 2) Activate the development mode - $python setup.py develop

回答6:

Make sure if root project directory is coming up in sys.path output. If not, please add path of root project directory to sys.path.