Sep 17 2012

Python Closure Gotcha

You know all about JavaScript closures. They’re great. We can do super cool stuff with them. Python has closures, too! However, the combination of closures and no var keyword leads us to a fun Gotcha.

Example of Gotcha:

def something_awesome():
    awesome = 1
    def increase_awesomeness():
        awesome = 2

    return awesome

You’d think that this would return 2, but it returns 1. This is due to Python creating a new local variable awesome inside the inner function. You can reach out of the closure when accessing a property. In places like these, since the inner function is used for utility only, I attach a property to it.

def something_awesome():
    def increase_awesomeness():
        increase_awesomeness.awesome += 1

    increase_awesomeness.awesome = 1
    return increase_awesomeness.awesome
  • #programming
  • #python
  • #planet