Modify int in place

0 votes

This is more of a curiosity

Say I have the following code

>>> my_immutable = (1, 2)
>>> my_immutable[0] += 1

TypeError: 'tuple' object does not support item assignment

This is expected, because unlike C, Python does not modify the underlying int, but rather creates a new one (observed in the code below)

>>> x = 1
>>> id(x)
33156200
>>> x += 1
>>> id(x)
33156176

If I want to modify the underlying integer in the tuple, I can hackly do something like

>>> hacked_immutable = ([1], [2])
>>> hacked_immutable[0][0] += 1
>>> hacked_immutable
([2], [2])

My question is: is there a nicer way of doing it (ideally performant and ideally already in the standard library)? Some wrapper class around int maybe?

Edit: I did not have a specific software that had to adhere to this. It was more of a thought exercise of why are things like this. I think the three questions I had were:

  • Why are ints immutable? (still not sure)

  • Is there a way to force them to be mutable? (wim's answer)

  • Is there a nice way to force them to be mutable (like Integer vs int in Java) - I think the answer is NO?

Thanks a lot for the discussion!

Sep 14, 2018 in Python by bug_seeker
• 15,480 points
63 views

1 answer to this question.

0 votes

Use a list rather than a tuple:

my_container = [1, 2]

tuple is immutable - you can't modify them.

int is immutable - you can't modify them.

The closest you can get is using ctypes to monkeypatch the value. But this is not "nice" by any stretch of the imagination and you will probably segfault your Python runtime if anything else happens to be using that integer.

>>> t = (42, 43)
>>> import ctypes
>>> ctypes.cast(id(42), ctypes.POINTER(ctypes.c_int))[6] = 666
>>> t
(666, 43)
answered Sep 14, 2018 by Priyaj
• 57,640 points

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