const arguments in Python

Question

I have an object (numpy.ndarray, for example), that should be passed as an argument to several functions. In C++ in such cases I declared such arguments as const, in order to show, that they must not be changed.

How can I do the same in Python?

If you want to define immutable array, using tuple is the answer for it. — Kei Minagawa
– Kei Minagawa, Commented Apr 20, 2014 at 11:32
@KeiMinagawa Tuples are not an acceptable substitute for numpy arrays because they are not suitable for serious numerical computation. — Nick Alger
– Nick Alger, Commented Jan 5, 2023 at 20:30

BartoszKP · Accepted Answer · 2019-09-13 13:08:34Z

8

Syntactically, you can't. You have two choices:

pass a copy of your object to these functions - this way, you won't have to worry about it being corrupted
create a wrapper, that implements the required interface, wraps your object, and doesn't allow modifications

The second option is of course only possible if you know what interface is expected and if it's simple.

edited Sep 13, 2019 at 13:08

answered Apr 20, 2014 at 10:50

BartoszKP

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1 Comment

Two-Bit Alchemist Over a year ago

I would add a third option (perhaps expanding on the second) that depending on what's really going on, this whole deal should be managed by a class (with the object as a data member and those functions as methods).

Felix · Accepted Answer · 2023-01-08 16:54:05Z

3

Well, there's a trick especially for numpy arrays:

array.flags.writable=False

answered Jan 8, 2023 at 16:54

Felix

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