recursive function in python to calculate sum of elements of a list
I am having difficulty in an exercise whose I should show the sum of all elements of a list recursively.
The code I came up with only has the basis of recursion, the recursion itself I did not, as I did not understand how it could be applied to some list.
I'll leave the code here for you to analyze:
def soma_lista(lista):
if len(lista) == 1:
return lista[0]
else:
for i in range (len(lista)):
soma = lista[i] + soma_lista(lista[i + 1])
return soma
Note: as I said, I don't know how to apply the recursion part, so I tried something random. Ignore else's code block.
3 answers
Recursion in this case would play the role of the repeating loop, so you don't need to use both. Your recursion stop condition is correct: if the list has only one element, return it. already in else, instead of the loop, you should return only the first element added with the function return to the rest of the list:
return lista[0] + soma_lista(lista[1:])
Where lista[1:] returns the list from the first element. That is, the sum of a list will be equal to the first element summed with the result of the sum of the rest of the list and thus the recursion is done:
def soma_lista(lista):
if len(lista) == 1:
return lista[0]
else:
return lista[0] + soma_lista(lista[1:])
See working on Ideone.
Recursion is the technique where a method or function calls itself to arrive at the result.
I implemented this in Pythonic Form:
def soma_lista(lista=list()):
'''
Calcula a somatória dos elementos de uma lista.
:param lista: lista de elementos inteiros
:return: int
>>> soma_lista([1,2,3])
6
>>> soma_lista([1,2,3,4])
10
>>> soma_lista([1,2,3,4,5,6])
21
'''
try:
return lista.pop() + soma_lista(lista)
except IndexError:
return 0
if __name__ == '__main__':
import doctest
doctest.testmod()
print()
E this conventionally:
def soma_lista(lista=list()):
'''
:param lista:
:return:
>>> soma_lista([1,2,3])
6
>>> soma_lista([1,2,3,4])
10
>>> soma_lista([1,2,3,4,5,6])
21
'''
if len(lista) >= 1:
return lista.pop() + soma_lista(lista)
else:
return 0
if __name__ == '__main__':
import doctest
doctest.testmod()
print()
A way that I consider to be very didactic to show the" mysteries " of recursion in this case:
def recl(l, i=0):
try:
elmnt = l[i]
i+=1
return elmnt + recl(l,i)
except:
return 0
print (recl([1,2]))
3