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Created on 2013-06-03 19:38 by bsdphk, last changed 2022-04-11 14:57 by admin. This issue is now closed.
| Messages (3) | |||
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| msg190557 - (view) | Author: Poul-Henning Kamp (bsdphk) | Date: 2013-06-03 19:38 | |
I'd like to nominate this piece of code as candidate for the next round of "Most unexpected python behaviour" awards:
def foo(a, x = []):
x.append(a)
return x
print(foo(1))
print(foo(2))
I expected the output to be:
[1]
[2]
but I get:
[1]
[1, 2]
Bug? (If not, I'd *love* to read the rationale for this behaviour...)
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| msg190558 - (view) | Author: Eric V. Smith (eric.smith) *  |
Date: 2013-06-03 19:58 | |
It's by design. Search for "mutable default arguments", for example http://docs.python-guide.org/en/latest/writing/gotchas.html#mutable-default-arguments |
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| msg190566 - (view) | Author: Barry A. Warsaw (barry) * |
Date: 2013-06-03 21:07 | |
While it's true that it can be confusing to users, it's not a bug. http://docs.python.org/2/reference/compound_stmts.html#function and a nice treatise on the subject by the Effbot: http://effbot.org/zone/default-values.htm |
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:57:46 | admin | set | github: 62327 |
| 2013-06-03 21:07:40 | barry | set | nosy:
+ barry messages: + msg190566 |
| 2013-06-03 19:58:45 | eric.smith | set | status: open -> closed nosy: + eric.smith messages: + msg190558 resolution: not a bug stage: resolved |
| 2013-06-03 19:38:11 | bsdphk | create | |