Different lists in list have same id in python

Asked Sep 07 '17 at 11:22

Active Sep 07 '17 at 11:22

Viewed 30 times

I understand that Python mutables like lists have different identities while "special situations" like certain strings and numbers will have the same IDs but I don't understand this situation:

>> a = [[0]*2]*2
>>> a
[[0, 0], [0, 0]]
>>> id(a[0])
140387455550664
>>> id(a[1])
140387455550664

Both [0,0] lists in the list a have the same ID

However, when I create a list like this, the IDs are different for each list element in that list

>>> b = [[0,0],[0,0]]
>>> id(b[0])
140387455550472
>>> id(b[1])
140387456353480

I am using CPython/Python 3.6 on Ubuntu

asked Sep 07 '17 at 11:22

sami

3

They are not different lists.. – Martijn Pieters Sep 07 '17 at 11:22
OK got it - just saw the duplicate answer/qs - thanks – sami Sep 07 '17 at 11:26
1

`a[0]` and `a[1]` are the same list object, which is why they have the same id. Your question title implies you think they are different lists. – Martijn Pieters Sep 07 '17 at 11:27
@MartijnPieters bit off-topic but noticed `id([]) == id([1])` is `True`? – Chris_Rands Sep 07 '17 at 11:32
1

@Chris_Rands: Yes, because ids can be re-used. `[]` does not live long enough to keep the id, so it is reused for `[1]`. – Martijn Pieters Sep 07 '17 at 11:32
1

@Chris_Rands: ids are unique *for the objects lifetime only*. – Martijn Pieters Sep 07 '17 at 11:33
@MartijnPieters Great, thank you, makes sense! – Chris_Rands Sep 07 '17 at 11:34

Different lists in list have same id in python

0 Answers0