python classes and variable scope

class Test:

    def c(self, args):
        print args开发者_如何学JAVA

    def b(self, args):
        args.append('d')

    def a(self):
        args = ['a', 'b', 'c']
        self.b(args)
        self.c(args)

Test().a()

Why doesn't this print ['a', 'b', 'c']?

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When you pass a list to a function, you're really passing it a pointer to the list and not a copy of the list. So b is appending a value to the original args, not its own local copy of it.

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The parameter you pass to methods b and c is a reference to the list args, not a copy of it. In method b, you append to the same list you created in method a.

See this answer for a more detailed explanation on parameter passing in Python.