Question

I have a python function func(A). A is a numpy.array and can be big such that I hesitate copying it over and over again. This func(A) wants to change the content of A. I know this a python newbie issue. I used to program in C and it could be done by pointers. How can I change the content of A so that the change is also valid outside the scope of the func(A)?

Answer 1

The tl;dr is in your case, it basically already is. Unless you assign a new value to the label A in the method, A will be a reference to the object you passed, which means any modifications to A will change the original object everywhere else you use it.

ex:

>>> def foo(A):
...     print A[0]
...     A[0] = 2
...     print A[0]
...
>>> a = [0, 1, 2]
>>> foo(a)
0
2
>>> a
[2, 1, 2]
>>> def bar(A):
...     print A[0]
...     A = [0, 1, 2]
...     A[0] = 2
...     print A[0]
...
>>> a = [0, 1, 2]
>>> bar(a)
0
2
>>> a
[0, 1, 2]