> From: Lee Fleming > On Aug 6, 12:30 pm, "Hamilton, William " <[EMAIL PROTECTED]> wrote: > > When you call f(23), the variable y within it gets created and points at > > None. When f(23) exits, the y that it created gets destroyed. (Well, > > goes out of scope, but even if it's not garbage collected it won't ever > > come back into scope.) When you then call f(24), a new y is created > > that also points to None, and disappears forever when f(24) exits. > > > > The values in a def statement are created when the def is executed, but > > the variables are only created when the function is actually called, and > > new ones are created every time the function is called. > > > > -- > > -Bill Hamilton- Hide quoted text - > > > > - Show quoted text - > > why isn't the y in def f (x, y = []): something > garbage-collected? >
The y is garbage-collected. However, the [] in the def statement is not. The list is created when the statement is evaluated. Every time that f() is called with a default value, the new y created will point to the same list. If that list is mutated into [23], it will still be [23] the next time f() is called, and the new y created in that call will point at the same list (now [23]) that the (now destroyed) y pointed to in the first call. -- -Bill Hamilton -- http://mail.python.org/mailman/listinfo/python-list
