How to resolve import errors in python?

问题:

I have a specific problem which might require a general solution. I am currently learning apache thrift. I used this guide.I followed all the steps and i am getting a import error as Cannot import module UserManager. So the question being
How does python import lookup take place. Which directory is checked first. How does it move upwards?
How does sys.path.append('') work?

I found out the answer for this here. I followed the same steps. But i am still facing the same issue. Any ideas why? Anything more i should put up that could help debug you guys. ?

Help is appreciated.

回答1:

On windows, Python looks up modules from the Lib folder in the default python path, for example from "C:\Python34\Lib\". You can add your Python libaries in a custom folder ("my-lib" or sth.) in there, but you need a file in order to tell Python that you can import from there. This file is called __init__.py , and is totally empty. That data structure should look like this:

my-lib

__init__.py

/myfolder

mymodule.py

(This is how every Python module works. For example urllib.request, it's at "%PYTHONPATH%\Lib\urllib\request.py")

You can import from the "mymodule.py" file by typing

import my-lib

and then using

mylib.mymodule.myfunction

or you can use

from my-lib import mymodule

And then just using the name of you function.

You can now use sys.path.append to append the path you pass into the function to the folders Python looks for the modules (Please note that thats not permanent). If the path of your modules should be static, you should consider putting these in the Lib folder. If that path is relative to your file you could look for the path of the file you execute from, and then append the sys.path relative to your file, but i reccomend using relative imports.

If you consider doing that, i recommend reading the docs, you can do that here: https://docs.python.org/3/reference/import.html#submodules

回答2:

If I got you right, you're using Python 3.3 from Blender but try to include the 3.2 standard library. This is bound to give you a flurry of issues, you should not do that. Find another way. It's likely that Blender offers a way to use the 3.3 standard library (and that's 99% compatible with 3.2). Pure-Python third party library can, of course, be included by fiddling with sys.path.

The specific issue you're seeing now is likely caused by the version difference. As people have pointed out in the comments, Python 3.3 doesn't find the _tkinter extension module. Although it is present (as it works from Python 3.2), it is most likely in a .so file with an ABI tag that is incompatible with Blender's Python 3.3, hence it won't even look at it (much like a module.txt is not considered for import module). This is a good thing. Extension modules are highly version-specific, slight ABI mismatches (such as between 3.2 and 3.3, or two 3.3 compiled with different options) can cause pretty much any kind of error, from crashes to memory leaks to silent data corruption or even something completely different.

You can verify whether this is the case via import _tkinter; print(_tkinter.file) in the 3.2 shell. Alternatively, _tkinter may live in a different directory entirely. Adding that directory won't actually fix the real issue outlined above.

回答3:

You may try with declaring sys.path.append('/path/to/lib/python') before including any IMPORT statements.