CODEWITHSUNDEEP
pythonrecursionreturn
user2246905
user2246905

Reputation: 1039

python tail recursive function doesn't return

I have a function that modifies a list, however it doesn't return anything. It is a long function but to give an example, the following has the same problem. Why is it not returning anything?

def inventedfunction(list1):
    list2=list1[:-1]
    if len(list2)!=1:
        inventedfunction(list2) 
    else:
        return list2

Upvotes: 0

Views: 86

Answers (2)

user4171906
user4171906

Reputation:

You didn't say what the function is supposed to do, so I am assuming that "inventedfunction" means "inverted function". Even if this is not correct, the idea is the same. If this is not the case or you don't understand then post back with more info.

You don't catch any of the returns, and don't return anything (None) if len(list2) != 1. You also would have to create a 2nd list to hold the numbers removed from the list sent to the function, and return the updated list as well according to way your code is structured.

def inventedfunction(list1, new_list=[]):
    ## at the least add print statements so you know what is happening
    print new_list, "----->",  list1
    list2=list1[:-1]
    new_list.append(list1[-1])  ## append item removed from list1 --> list2
    if len(list2):
        new_list, list2=inventedfunction(list2)
    return new_list, list2  ## both updated lists returned

print inventedfunction([1, 2, 3, 4, 5])

Upvotes: 0

Elliot Gorokhovsky
Elliot Gorokhovsky

Reputation: 3762

Replace inventedfunction(list2) with return inventedfunction(list2). If you just call it without the return statement, the result is thrown out.

Working code:

def inventedfunction(list1):
    list2=list1[:-1]
    if len(list2)!=1:
        return inventedfunction(list2) 
    else:
        return list2

Upvotes: 2

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