Python 3.6 tuple strange behavior?

Asked Sep 14 '18 at 13:10

Active Sep 14 '18 at 13:13

Viewed 62 times

Can somebody explain why does Python 3.6 behaves so strange in this piece of code?

a = (1, 2, [5, 6])
a[2]+=[7, 8]
print(a)

Output:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment
>>>print(a)
(1, 2, [5, 6, 7, 8])

edited Sep 14 '18 at 13:13

asked Sep 14 '18 at 13:10

Chiefir

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What is the result, and what did you expect? – glibdud Sep 14 '18 at 13:11
1

I want to point out this is way more subtle than it seems. += usually extends in place – Olivier Melançon Sep 14 '18 at 13:12
1

@JonasWolff Yea but the list inside can be. And it does update – Vineeth Sai Sep 14 '18 at 13:14
Even if you get an exception on `a[2]+=[7, 8]` the list is updated. I guess the question is based on this fact. – Szabolcs Dombi Sep 14 '18 at 13:18
One might expect is that replacing `a[2]+=[7, 8]` by `a[2].extend([7,8])` would have the same behaviour. It does, but no error message. – BoarGules Sep 14 '18 at 13:20

Python 3.6 tuple strange behavior?

0 Answers0