Closures in Python and JavaScript

Here is a program written in Python:

def clo():
   a = 3
   def geta():
       return a
   def seta(newa):
       a = newa
   return [geta, seta]

closure = clo()
closure[1](5)
print(closure[0]())

And here is the same program written in JavaScript:

function clo() {
   var a = 3;
   function geta() {
       return a;
   }
   function seta(newa) {
       a = newa;
   }
   return [geta, seta];
}

closure = clo()
closure[1](5)
print(closure[0]())

Here is the output of running the Python program:

tuba:~ litherum$ python --version
Python 2.5.1
tuba:~ litherum$ python test.py
3

And here is the output of running the JavaScript program:

tuba:~ litherum$ java -jar Downloads/rhino1_7R2/js.jar test.js
5

Here are a couple observations of this:

• Both languages printed out a value, so clearly both of them use closures
  


• Python printed out the original value of a, so it appears that it creates a new closure for each function invocation.
  


• JavaScript printed out the new value of a, so it appears that the closure is consistent across function invocations
  

I just noticed this and thought that it's fairly interesting food for thought.