Using of 2 for loop

Question

I want to get information from user, and show it with for loop. I wrote this code:

name=["Name","Age","Gender"]
n=str(input())
a=int(input())
g=str(input())
nameinput=[n,a,g]
for i in name:
    for j in nameinput:
        print(i,j)

I expect the output of code to be:

Name Fuad, Age 18, Gender M

but the actual output is

Name Fuad Name 18 Name M Age Fuad Age 18 Age M Gender Fuad Gender 18 Gender M

How I can fix this problem and please can you explain why my code isn't running

Answer 1

You are doing nested loops which iterates the cartesian product (every element of name is paired with every element of nameinput ). You want to do pair-wise iteration of multiple iterables, which is achieved by zip :

for i, j in zip(name, nameinput):
    print(i,j)

The workings of zip can be illustrated by the following example:

list(zip([1, 2, 3], [4, 5, 6]))
# [(1, 4), (2, 5), (3, 6)]

Nested loops, however, would do:

>>> [(i, j) for i in [1, 2, 3] for j in [4, 5, 6]]
[(1, 4), (1, 5), (1, 6), (2, 4), (2, 5), (2, 6), (3, 4), (3, 5), (3, 6)]

If you think through your loop code step-by-step, that logic should become clear.