[ Python 常見問題 ] Expand Python Search Path to Other Source

Source From Here
Question
I have just joined a project with a rather large existing code base. We develop in linux and do not use and IDE. We run through the command line. I'm trying to figure out how to get python to search for the right path when I run project modules. For instance, when I run something like:

# python someprojectfile.py

I get:

ImportError: no module named core.'somemodule'

I get this for all of my imports to I assume it's an issue with the path.

How-To
There are a few possible ways to do this:

* Set the environment variable PYTHONPATH to a colon-separated list of directories to search for imported modules.
* In your program, use sys.path.append('/path/to/search') to add the names of directories you want Python to search for imported modules. sys.path is just the list of directories Python searches every time it gets asked to import a module, and you can alter it as needed (although I wouldn't recommend removing any of the standard directories!). Any directories you put in the environment variable PYTHONPATH will be inserted into sys.path when Python starts up.
* Use site.addsitedir to add a directory to sys.path. The difference between this and just plain appending is that when you use addsitedir, it also looks for .pth files within that directory and uses them to possibly add additional directories to sys.path based on the contents of the files. See the documentation for more detail.

Which one of these you want to use depends on your situation. Remember that when you distribute your project to other users, they typically install it in such a manner that the Python code files will be automatically detected by Python's importer (i.e. packages are usually installed in the site-packages directory), so if you mess with sys.path in your code, that may be unnecessary and might even have adverse effects when that code runs on another computer. For development, I would venture a guess that setting PYTHONPATH is usually the best way to go.

However, when you're using something that just runs on your own computer (or when you have nonstandard setups, e.g. sometimes in web app frameworks), it's not entirely uncommon to do something like:

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1. #!/usr/bin/env python  
2. from os.path import dirname  
3.   
4. print __file__  # The full path of this py file  
5. print dirname(__file__)  # Get the directory path of this py file  
6. sys.path.append(dirname(__file__)) # Add the directory of this py file to search path of python source file