Semantics of Python

 def mkcounter(a):
 def f():
 a = a + 1
 print a
 return f

 UnboundLocalError: local variable 'a' referenced before assignment

• So they tell you to do this:

 def mkcounter(a):
 def f(a=a):
 a = a + 1
 print a
 return f

• But now it doesn't close

• You can get closures, sort of

  • But the closed-over values are read-only

Closures aren't important.

--Guido van Rossum