Relative importing python module from a subfolder from a different subfolder

Question

I'm trying to use alembic which is an sqlalchemy tool in python. You type a command and it generates a folder "alembic" with py files inside. The py file inside, needs to link to my application in a separate folder called "myapp". But I cannot link it. It says it doesn't exist and relative import doesn't work.

so I need to import my config class from myapp/configs/config.py file.

/apps
+--/alembic
|----env.py <--- the calling file
+--/myapp
|----configs/__init__.py <--- has "DefaultConfig" class imported
|----configs/config.py <--- I want to import the class inside here.

inside env.py:

from myapp.configs import DefaultConfig

Doesn't work.

I tried:

from ..myapp.configs import DefaultConfig

No success.

example code in alembic docs say just use "myapp.whatever".

I even added my "/apps" and "/myapp" to PYTHON_PATH in environment variables.

Example error:

File "D:\apps\myapp\lib\site-packages\alembic\command.p
y", line 97, in revision
    script.run_env()
  File "D:\apps\myapp\lib\site-packages\alembic\script.py
", line 191, in run_env
    util.load_python_file(self.dir, 'env.py')
  File "D:\apps\myapp\lib\site-packages\alembic\util.py",
 line 186, in load_python_file
    module = imp.load_source(module_id, path, open(path, 'rb'))
  File "alembic\env.py", line 5, in <module>
    from ..myapp.configs import DefaultConfig as conf
ValueError: Attempted relative import in non-package

Answer 1

You have two possible solutions to your problem:

Modify your PYTHONPATH environment variable

Add the path to apps catalogue by running following BASH / SH shell commands in your terminal:

$ export PYTHONPATH=$PYTHONPATH:'/path/to/apps'

Please not that adding it to the PATH environment variable won't work. To find out more about PYTHONPATH, how to manage it plus nice and friendly info on modules in general:

http://www.stereoplex.com/blog/understanding-imports-and-pythonpath

Please note however that this approach does affect your system's PYTHONPATH. It is highly recommended to use a virtualenv - just in case things go wrong, it won't affect all your system and other apps. When using virtualenvwrapper:

$ add2virtualenv '/path/to/apps'

More HERE.

Append path from inside the Python script

Alternatively, you can do the same but just for a script runtime by adding:

import sys
sys.path.append('/path/to/apps')

to your apps/alembic/env.py file.

Finally, in same file, make a following change:

from myapp.configs.config import DefaultConfig

And please note that your apps/myapp folder should also contain __init__.py file (might be empty) to make Python to treat is as a module as Demian Brecht pointed out.