How do you modify sys.path in Google App Engine (Python)?

Question

I've tried adding the following line to my handler script (main.py), but it doesn't seem to work:

sys.path.append('subdir')

subdir lives in the my root directory (i.e. the one containing app.yaml).

This doesn't seem to work, because when I try to import modules that live in subdir, my app explodes.

Answer 1

1) Ensure you have a blank __init__.py file in subdir.

2) Use a full path; something like this:

import os
import sys

sys.path.append(os.path.join(os.path.dirname(__file__), 'subdir'))

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Edit: providing more info to answer questions asked in a comment.

As Nick Johnson demonstrates you can place those three lines of code in a file called fix_path.py. Then, in your main.py file, do this import fix_path before all other imports. Link to a tested application using this technique.

And, yes, the __init__.py file is required; per the documentation:

When importing the package, Python searches through the directories on sys.path looking for the package subdirectory.

The __init__.py files are required to make Python treat the directories as containing packages; this is done to prevent directories with a common name, such as string, from unintentionally hiding valid modules that occur later on the module search path. In the simplest case, __init__.py can just be an empty file, but it can also execute initialization code for the package or set the __all__ variable, described later.

Answer 2

It worked for me inserting the new dirs as the first entries in sys.path.

path_changer.py:

import os
import sys

sys.path.insert(0, os.path.join(os.path.dirname(__file__), 'libs'))
sys.path.insert(1, os.path.join(os.path.dirname(__file__), 'apps'))

app.py:

import path_changer
from google.appengine.ext.webapp.util import run_wsgi_app

from flask import Flask
import settings

app = Flask('myapp')
app.config.from_object('settings')

from website import views as website_views

run_wsgi_app(app)