CODEWITHSUNDEEP
pythonlistfor-loopproduct
StacyM
StacyM

Reputation: 1036

Python 3+ - for in range loop, multiply, product, list NOT using mul or lambda or for in loop

I'm taking this online Python course and a common theme in this course is to NOT use functions or libraries to solve solutions. The problem asks:

Define a function prod(L) which returns the product of the elements in a list L.

My attempt is below. This specific problem asks to use for in range, the next question uses for in. I understand how to use for in, but not for in range. How do use the range i of 0,1,2,3 to help calculate the product?

broken for in range loop:

def prod(L):
   Llen = len(L)
   for i in range (0,Llen):
      print(L[-1]*L[-2]*L[-3]*L[-4])

prod([1,2,3,4])

My for in loop works fine.

def prod(L):
   p = 1
   for i in L:
      p *= i
   return p

prod([1,2,3,4])

Please no lambda or 'from operator import mul'! I understand those methods.

Upvotes: 0

Views: 2938

Answers (4)

CT Zhu
CT Zhu

Reputation: 54330

Using math library allowed? That will be easy (doing it in numpy would be sort-of cheating):

>>> from math import *
>>> def prod(L):
        if 0 in L:
            return 0.
        #elif len(L)==0:
        #    return 0.
        elif sum([item<0 for item in L])%2==0
            return exp(sum(map(log, L)))
        else:
            return -exp(sum(map(log, map(abs, L))))

Upvotes: 0

Hyperboreus
Hyperboreus

Reputation: 32429

Another way how to solve it (up to max recursion depth) using range:

def prod (x):
    range (42)
    def prod_ (head, *tail):
        return head if not tail else head * prod_ (*tail)
    return 1 if not x else prod_ (*x)

print (prod ( [1, 2, 5, 19] ) )

Upvotes: 0

DhruvPathak
DhruvPathak

Reputation: 43235

>>> x = [2,3,4,7]
>>> len(x)
4
>>> range(0,len(x))
[0, 1, 2, 3]
>>> range(len(x))
[0, 1, 2, 3]
>>> def prod(L):
...     p = 1
...     for i in range(len(L)):
...             p = p*L[i]
...     return p
... 
>>> prod(x)
168

Upvotes: 0

alecxe
alecxe

Reputation: 473793

The idea is pretty much the same as for in. Note that you don't need to make a variable from the list length, also you don't need to specify a start for the range(), it's 0 by default. 

def prod(L):
    p = 1
    for i in range(len(L)):
        p *= L[i]
    return p

print(prod([1,2,3,4]))  # prints 24

Upvotes: 1

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