Tracking Python function calls

It is sometimes useful to track the number of calls against a certain function in Python somewhere deep in the internals of the system. Turns out the Python global keyword can help with this.

Consider the following module:

   ### foo.py ###

   def foo( ):
      pass

   ### foo.py ###

Assuming that the foo module is imported at some point during execution with import foo or from foo import foo rather than being run as a script in its own right, the following use of global is possible:

   ### foo.py ###

   visits = 0

   def foo( ):
      global visits
      visits += 1
      print 'visit number %s' % visits

   ### foo.py ###

Each call against foo( ) will now increment the global visits counter and print to standard out.

A not-bad use of global indeed.