Question

I’ve got a dynamic Python service that will be defining functions on a per-record basis and I ran into something I couldn’t quite figure out. Say I’ve got a test program set up like so:

func_str = """
def func():
  print "top"
"""
exec func_str

func_str = """
def func():
  print "bottom"
"""
exec func_str

func()

This will, of course, print "bottom", as the second call to exec func_str overwrites the first. I’m curious what happens under the hood. Is the first function definition deleted in some way?

Answer 1

The function body is compiled, then it assigned to the local namespace under the variable name func.

When you then run the second exec statement a new function is stored under that same name, overwriting the first. You can preserve the first one by storing a reference to it in a new name:

foo = func

so you can later on refer to it still as foo:

foo()

You could also store it in a dictionary, a list, or as an attribute on another object.