I want to calculate the sum of a list without using mutation.
def noMutSum(lst, pointer=0, result=0):
if pointer == len(lst):
return result
newResult = result + lst[pointer]
return noMutSum(lst, pointer+1, newResult)
Is changing the pointer considered mutating when stepping into the recursion,
or does mutation only involve variable changes in an iterative loop?
By not mutating pointer, you are passing a distinct value into each call of noMutObj. Each stack frame maintains its own unique pointer, none of which are altered. Even if you were to change it, only your local copy would be affected.
If you wanted to induce mutation, the approach could involve something like this:
lst.append(newResult)
return noMutObj(lst, pointer+1, newResult)
Prior to making this call. On the contrary, sending an adjusted list to the subsequent call should ideally be executed as follows:
return noMutObj(lst[:].append(newResult), pointer+1, newResult)
This method generates a fresh list, appends newResult and transfers this temporary object to the next step.
I realize that this isn't aligned with your intended function objective; I'm just demonstrating syntactic and semantic principles.
UPDATE
Ah ... now that we have a defined purpose ...
Mutation:
def noMutObj(lst):
if len(lst) == 0:
return 0
return lst.pop() + noMutObj(lst)
No mutation:
def noMutObj(lst):
if len(lst) == 0:
return 0
return lst[0] + noMutObj(lst[1:])
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