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Created on 2010-06-28 21:34 by muzuiget, last changed 2022-04-11 14:57 by admin. This issue is now closed.
| Messages (2) | |||
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| msg108872 - (view) | Author: muzuiget (muzuiget) | Date: 2010-06-28 21:34 | |
platform: ubuntu 10.04 amd64, python 2.6.5 r265:79063
run below code
a = [{}, {}, {}]
b = [{}] + [{}] + [{}]
c = [{}] * 3
print a, len(a), type(a)
print b, len(b), type(b)
print c, len(c), type(c)
a[1]["test"] = 1234
b[1]["test"] = 1234
c[1]["test"] = 1234
print a
print b
print c
the output is
[{}, {}, {}] 3 <type 'list'>
[{}, {}, {}] 3 <type 'list'>
[{}, {}, {}] 3 <type 'list'>
[{}, {'test': 1234}, {}]
[{}, {'test': 1234}, {}]
[{'test': 1234}, {'test': 1234}, {'test': 1234}]
each dict key in variable c seen to assign with the same value.
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| msg108873 - (view) | Author: Ezio Melotti (ezio.melotti) *  |
Date: 2010-06-28 21:40 | |
That's because with [{}] * 3 you get a list with 3 copies of the same object, so all the elements in c refer to the same dict:
>>> a = [{}, {}, {}]
>>> b = [{}] + [{}] + [{}]
>>> c = [{}] * 3
>>> map(id, a)
[12850496, 12850784, 12850928]
>>> map(id, b)
[12851648, 12851072, 12851792]
>>> map(id, c)
[12852080, 12852080, 12852080]
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:57:02 | admin | set | github: 53354 |
| 2010-06-28 21:40:11 | ezio.melotti | set | status: open -> closed nosy: + ezio.melotti messages: + msg108873 resolution: not a bug stage: resolved |
| 2010-06-28 21:34:58 | muzuiget | create | |