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+--- Thread: how to refer to a subset of a list (/thread-36088.html)
how to refer to a subset of a list - Skaperen - Jan-15-2022
i have a function that is given a list and it stores a special value into the first position (index 0) of that list.
def store_special_value(where_to_store):
...
if isinstance(where_to_store,list):
where_to_store[0] = special_value
returni want to call that function and put that value into the n-th element a list:def main(args)
...
target = []
...
temp_list = [None]
store_special_value(temp_list)
target[n] = temp_list[0]
...my question is: is there a more direct way to do this without using the temporary list? that would mean a list reference that refers to a subset of an existing list (target) but operates as if it were a whole list. list slicing creates a new list instead of referring to an existing given list, so that is not a solution. is there a way to make a subset reference like that?i do have a real use case for this, which is more complicated, but, i prefer to work with a minimal example case, to determine a more general use solution.
RE: how to refer to a subset of a list - BashBedlam - Jan-15-2022
Do you mean like this?
special_value = 13 my_list = [1, 2, 3, 4, 5] my_list.insert (2, special_value) print (my_list)
Output:[1, 2, 13, 3, 4, 5]RE: how to refer to a subset of a list - Skaperen - Jan-15-2022
what i need is a way to use a function that will store into index 0 (that part cannot be changed) by giving it a subset reference. so if i want it to store into index 47 i would create a subset that starts at 47, such that accessing the subset at 0 accesses the original list at 47. subset[1] would be original[48]. this is done in pointer oriented languages by adding to the pointer. i don't know if it could be done in Python since i don't know the details of how it stores a list in memory. but there are ways to do it.
RE: how to refer to a subset of a list - deanhystad - Jan-16-2022
He wants a C pointer like thing.
int x[10]; int *y = &x[2];
RE: how to refer to a subset of a list - Skaperen - Jan-16-2022
yes.
but i can envision a way to do it in an implementation of a list like object that contains values or references to other objects, with an interface API to this which can be done with methods.
fake_list = real_list.subset(47,99)
assert fake_list[0:52] == real_list[47:99]i simply don't know if any implementation ever did this, like Python or Pike. i don't even want to look at Peril.