Python import modules from a higher level package

问题

This is my package hierarchy

app  
|--__init__.py    //Empty file
|--server.py  
|--global_vars.py  
|
|--handlers    
   |--__init__.py    //Empty file
   |
   |--url1
   |  |--__init__.py    //Empty file
   |  |--app1.py
   |  |--app2.py
   |
   |--url2
      |--__init__.py    //Empty file
      |--app3.py

Now I want to import global_vars.py inside app1.py. So I gave import app.global_vars.py inside app1.py.

But I get the following error:

    import app.global_vars
ImportError: No module named app.global_vars

I should also mention that I am importing app1.py from server.py. server.py is the file I am actually running. When server.py imports app1.py, app1.py tries to import global_vars.py and I get the above mentioned error

What am I doing wrong here?

回答1:

If you are running app/server.py as a script, the parent directory of app is not added to sys.path(). The app directory itself is added instead (not as a package but as a import search path).

You have 4 options:

Move server.py out of the app package (next to it)
Add a new script file next to app that only runs:
```
from app import server
server.main()
```
Use the -m switch option to run a module as the main entry point:
```
python -m app.server
```
Add the parent directory of server.py to sys.path:
```
import os.path
import sys

parent = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
sys.path.insert(0, parent)
```
This last option can introduce more problems however; now both the app package and the modules contained in the app package are on sys.path. You can import both app.server and server and Python will see these as two separate modules, each with their own entry in sys.modules, with separate copies of their globals.