ValueError: could not convert string to float: '.' using for loop in Python

Question

My code receives two lines of input and splits those into lists. The result should look like:

input

4 6
2 4

output

2.0 1.5

I'm very new to coding, so my code isn't the most efficient, but here it is:

U = list(input().split(" "))
I = list(input().split(" "))
for z in range(len(U)):
    for x in U[z]:
        for y in I[z]:
            R = float(x) / float(y)
            print(round(R, 1), end=" ")

When I remove for x in U[z]: it works perfectly fine, except it prints every possible result. It also works fine with integers without removing the z loop. The full code for floats, however, prints ValueError: could not convert string to float: '.'. Is there a way to fix this without messing with the code too much?

Which version of Python are you using? I just executed exactly that and the output is 2.0 1.5, no errors. The input I used was 4 6, then hit Enter, then 2 4 and Enter again — MatBBastos
– MatBBastos, Commented Nov 19, 2021 at 21:54
You don't need to call list(), split() always returns a list. — Barmar
– Barmar, Commented Nov 19, 2021 at 21:57
Just some small things. .split() returns a list, so there's no reason to use list() there. Also, you can replace the 3 for loops with one by using for x,y in zip(U,I):. — gen_Eric
– gen_Eric, Commented Nov 19, 2021 at 21:58
Please explain what you're trying to do. There are many possible solutions to fixing your code but you haven't provided any details about what the intended behavior is. — hyperneutrino
– hyperneutrino, Commented Nov 19, 2021 at 21:59

azro · Accepted Answer · 2021-11-19 21:58:33Z

1

Your code works fine, but only for one digit number. As you iterate on each string value, 14 would generate '1' '4'

Just keep the outer iteration

for z in range(len(U)):
    print(round(float(U[z]) / float(I[z]), 1))

Or even better with zip

U = input(">>").split(" ")
I = input(">>").split(" ")
for x, y in zip(U, I):
    print(round(float(x) / float(y), 1))

answered Nov 19, 2021 at 21:58

azro

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Barmar · Accepted Answer · 2021-11-19 22:00:05Z

1

You shouldn't be looping over U[z] and I[z]. Those are strings, so you're iterating over the characters. And with nested loops, you're making a cross-product of all the characters in each list element.

Just use one loop over the indexes.

U = input().split(" ")
I = input().split(" ")
for z in range(len(U)):
    x = U[z]
    y = I[z]
    R = float(x) / float(y)
    print(round(R, 1), end=" ")

Or use zip() to loop over the two lists in parallel:

for x, y in zip(U, I):
    R = float(x) / float(y)
    print(round(R, 1), end=" ")

answered Nov 19, 2021 at 22:00

Barmar

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