Where to trigger ast modifications in Python?

I'm doing some AST modifications in Python. This may be done for optimization purpose or other.

Where is the right place to put it, so when you do something like:

python myfile.py

or

python runserver.py 开发者_Go百科myapp

the modifications took place for every .py executed file?

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Put your modifications in a site.py or sitecustomize.py (Python < 2.6) file (in the lib/site-packages directory ; Python will try to import and run it @ interpreter startup).