class Test:
def c(self, args):
print args
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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BTW, this has nothing to do with Python classes or variable scope. It's pass-by-value vs. pass-by-reference. Python uses the latter for objects. – Michael Lorton May 13 '11 at 01:56
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I wish I could accept both as answers. I appreciate the link that mizo provided but I'm marking Wern as the answer for two reasons: a) He posted first b) He has only been a member for 11 days now. – Russell May 13 '11 at 12:43
2 Answers
2
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.
Wern
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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.
