Sum of integers in a list in Python - def Recursive_function(one-argument)

Question

Sum of the elements (representing integers) in a list. For ex. A = ["xx", "3e", "5", "44"]

My function returns 49. So, the RECURSIVE one should do the same.

I implemented the ITERATIVE version successfully.

def add_iter(my_list):
    t = 0
    for x in my_list:
        if x.isdigit() == True:
            t+= int(x)
    print(t)

I would like to convert it to RECURSIVE function.

I have been pushing to think a solution without defining new variables... # scan all elements, remove non-integers, return sum... Makes no sense to define new variables in the function and do the recursion. Confused here. @JosephBudin — Ines
– Ines, Commented Sep 30, 2019 at 9:35
"a" was a list to test. a = ["aa", "a3", "33", "5"] for example... It works successfully when I call add_iter(a) — Ines
– Ines, Commented Sep 30, 2019 at 9:37
So why you give your function add_iter a parameter my_list? Inside your function you should work with that, instead of the variable defined outside the function (A) — AnsFourtyTwo
– AnsFourtyTwo, Commented Sep 30, 2019 at 9:44

Martin Bonner supports Monica · Accepted Answer · 2019-09-30 09:36:15Z

2

Since it's an exercise, i'm not writing the answer, but giving some hints

The sum of an empty list is zero
the sum of a non-empty list is (the first element) + (sum of the rest of the list)
the first element might be ignored if it's not a number

edited Sep 30, 2019 at 9:36

Martin Bonner supports Monica

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answered Sep 30, 2019 at 9:34

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Comments

fixatd · Accepted Answer · 2019-09-30 09:42:00Z

The recursive version functions similarly where you only iterate through each element before recursing to the remainder of the list. Your base case would be when the list only has one element left. I would suggest making a helper class to ensure that your values are valid numbers

# Helper function to clean up int value
def zero_or_value(value):
  try:
    return int(value)
  except ValueError as err:
    # Handler err here if you want
    pass
  return 0


def recursive_add_iter(my_list):
  if not my_list: # Return 0 if list is empty
    return 0
  elif len(my_list) == 1: # Base case, try converting last element
    return zero_or_value(my_list[0])

  return zero_or_value(my_list[0]) + recursive_add_iter(my_list[1:])


A = ["xx", "3e", "5", "44"]

print(recursive_add_iter(A))

AnsFourtyTwo · Accepted Answer · 2019-09-30 09:43:09Z

0

Try this:

def add_recursive(my_list):
    if my_list:
        x = my_list[0]
        if x.isdigit():
            return int(x) + add_recursive(my_list[1:])
        else:
            return add_recursive(my_list[1:])
    else:
        return 0


A = ["xx", "3e", "5", "44"]
add_recursive(A)
# 49

answered Sep 30, 2019 at 9:43

AnsFourtyTwo

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Comments

Ajax1234 · Accepted Answer · 2019-09-30 15:05:55Z

0

Shorter recursive solution:

def add_iter(d):
  return (0 if not d[0].isdigit() else int(d[0]))+(0 if not d[1:] else add_iter(d[1:]))

A = ["xx", "3e", "5", "44"]
print(add_iter(A))

Output:

answered Sep 30, 2019 at 15:05

Ajax1234

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