Since functions are values in Python, how do I determine if the variable is a function?

For example:

boda = len   # boda is the length function now
if ?is_var_function(boda)?:
  print "Boda is a function!"
else:
  print "Boda is not a function!"

Here hypothetical ?is_var_function(x)? should return true if x is a callable function, and false if it is not.

Please advise!

Thanks, Boda Cydo.