Can't import my own modules in Python

问题:

I'm having a hard time understanding how module importing works in Python (I've never done it in any other language before either).

Let's say I have:

myapp/__init__.py
myapp/myapp/myapp.py
myapp/myapp/SomeObject.py
myapp/tests/TestCase.py

Now I'm trying to get something like this:

myapp.py
===================
from myapp import SomeObject
# stuff ...

TestCase.py
===================
from myapp import SomeObject
# some tests on SomeObject

However, I'm definitely doing something wrong as Python can't see that myapp is a module:

ImportError: No module named myapp

回答1:

In your particular case it looks like you're trying to import SomeObject from the myapp.py and TestCase.py scripts. From myapp.py, do

import SomeObject

since it is in the same folder. For TestCase.py, do

from ..myapp import SomeObject

However, this will work only if you are importing TestCase from the package. If you want to directly run python TestCase.py, you would have to mess with your path. This can be done within Python:

import sys
sys.path.append("..")
from myapp import SomeObject

though that is generally not recommended.

In general, if you want other people to use your Python package, you should use distutils to create a setup script. That way, anyone can install your package easily using a command like python setup.py install and it will be available everywhere on their machine. If you're serious about the package, you could even add it to the Python Package Index, PyPI.

回答2:

The function import looks for files into your PYTHONPATH env. variable and your local directory. So you can either put all your files in the same directory, or export the path typing into a terminal::

export PYTHONPATH="$PYTHONPATH:/path_to_myapp/myapp/myapp/"

回答3:

exporting path is a good way. Another way is to add a .pth to your site-packages location. On my mac my python keeps site-packages in /Library/Python shown below

/Library/Python/2.7/site-packages

I created a file called awesome.pth at /Library/Python/2.7/site-packages/awesome.pth and in the file put the following path that references my awesome modules

/opt/awesome/custom_python_modules

回答4:

You can try

from myapp.myapp import SomeObject

because your project name is the same as the myapp.py which makes it search the project document first

回答5:

In your first myapp directory ,u can add a setup.py file and add two python code in setup.py

from setuptools import setup
setup(name='myapp')

in your first myapp directory in commandline , use pip install -e . to install the package

回答6:

In my case it was Windows vs Python surprise, despite Windows filenames are not case sensitive, Python import is. So if you have Stuff.py file you need to import this name as-is.

回答7:

pip install on Windows 10 defaults to installing in 'Program Files/PythonXX/Lib/site-packages' which is a directory that requires administrative privileges. So I fixed my issue by running pip install as Administrator (you have to open command prompt as administrator even if you are logged in with an admin account). Also, it is safer to call pip from python.
e.g.
python -m pip install <package-name>
instead of
pip install <package-name>