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

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Copyright 2005 M. J. Dominus