How to set the data type of a function parameter in python?

Question


def recursiveSum(lst):
    if len(lst) == 0:
        return 0
    else:
        #print(str(type(lst))+'\n')    
        num = lst[len(lst)-1]
        return recursiveSum(lst.pop()) + num


size = int(input("How many number do you want to enter? = "))
lst=[]
for i in range(size):
    lst.append(input("Enter number "+str(i+1)+" = " ))
print(recursiveSum(lst))

In this code i am trying to find sum of list of numbers recursively , this is my first attempt with recursions , i think my approach and algorithm was correct , the list when passed to the recursiveSum() function somehow makes it string in the else part , the commented line when executed ends up printing

class 'list'

class 'str'

I don't understand how the print statement prints both list and str.

Can someone explain this ?

because your input is a list of strings - not of numbers.

Patrick Artner
– Patrick Artner

2020-05-21 09:52:39 +00:00
Commented May 21, 2020 at 9:52 — Patrick Artner
– Patrick Artner, Commented May 21, 2020 at 9:52

Rajat Jain · Accepted Answer · 2020-05-21 09:51:50Z

3

I think you forgot to type cast to int when input:

lst.append(int(input("Enter number "+str(i+1)+" = " )))

answered May 21, 2020 at 9:51

Rajat Jain

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1 Comment

Błotosmętek Over a year ago

Besided: lst.pop() returns the last element of lst, not the list without last element; and lst[len(lst)-1] can be more elegantly written as lst[-1]

Patrick Artner · Accepted Answer · 2020-05-21 09:55:26Z

2

Two problems:

you do not convert your inputs into numerics/integers
you recurse using the popped element not the remaining list

Fix:

def recursiveSum(lst):
    if len(lst) == 0:
        return 0
    else:
        num = lst[0]   # use the first one 
        return recursiveSum(lst[1:]) + num   # and recurse on the remaining slice


size = int(input("How many number do you want to enter? = "))
lst=[]
for i in range(size):
    lst.append(int(input("Enter number "+str(i+1)+" = " )))
print(recursiveSum(lst))

list.pop() returns the element popped from the list - not the list-remainder.

answered May 21, 2020 at 9:55

Patrick Artner

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