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Python bug with [] as default value in functions?
Duncan Boothduncan at rcp.co.uk
Thu Apr 12 08:53:48 EDT 2001
[posted and mailed]Dinu Gherman <gherman at darwin.in-berlin.de> wrote in <3AD5989D.E22E2CBF at darwin.in-berlin.de>:> I noticed a very strange behaviour: I've got a recursive func-> tion like this:>> foo(spam, eggs=[]):> ...> return foo(spam, eggs=eggs)> # the following is the same:> # return foo(spam, eggs)>> where the default argument for eggs, the empty list, is *empty*> for the top-level call *only* when it is explicitly provided> with the function call like this:>> bar = foo(mySpam, eggs=[])>This is documented behaviour. See the FAQ athttp://www.python.org/doc/FAQ.html#6.25 for a description.In general if you want a mutable object to be used as a default argument (and the function needs to modify the object), use None instead and create the object inside the function.
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