Good with a keyboard and fluent in gibberish
Posted 07 Oct 2014

Python Path conflict

I have found an… odd collision of problems. I have the following packages installed:

  • Twisted
  • Google protocol buffers (google.protobuf)
  • The google package from PyPI (not affiliated)

Twisted provides an application system which lets you define .tac files and then have twistd handle a bunch of boiler plate (logging, background, reactor selection, etc).

  1. twistd is installed as a Python file to my PATH (ie /usr/bin)
  2. google installs google.py to my PATH (/usr/bin)
  3. When you start twistd, Python adds its directory (/usr/bin) to its path
  4. When my application imports google.protobuf, Python first imports google
  5. Python finds /usr/bin/google.py and imports it as google
  6. Python can’t find protobuf in google.

So what went wrong?

  • twistd was installed in such a way to allow unnecessary items into Python’s path
  • google installed a .py file into the PATH
  • I wasn’t using a virtual environment.

I’m now considering the opinion that Python scripts should never be installed directly. Instead, they should be installed as __main__ modules and a shell script of the form exec python2/3 -m mypackage is installed to your PATH.