Why won't Python store 0 in list?

Question

I have the following code that takes an input number, multiplies the first digit by 3 and then prints out the first digit. When I input 023, it gives me 6 instead of 0. Why is that?

a=int(input())

b=str(a)

c=int(b[0])*3

print(c)

You're converting the input string to int, so the leading zero is removed. — toti08, Oct 15 '18 at 12:32
Loop around the `input()` to validate the input is an `int` before proceeding, but don't convert the input to `int` unless you need to. — r.ook, Oct 15 '18 at 12:45
Why don't you make the user enter a list of integers? For doing that, I suggest you to follow [this answer](https://stackoverflow.com/questions/4663306/get-a-list-of-numbers-as-input-from-the-user). — Tommaso Di Noto, Oct 15 '18 at 12:40

score 2 · Answer 1 · edited Oct 15 '18 at 12:39

2

You are doing:

a=int(input())

So if input() = '023', int('023') will be 23. So a=23

b=str(a) => b='23'

int(b[0]) => c=2*3=6

You should do:

 a=input()

then

c=int(a[0])*3

edited Oct 15 '18 at 12:39

Rahul Agarwal

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answered Oct 15 '18 at 12:37

ThisIsMyName

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This works but it also allows suspicious inputs to go through, such as `3foo`, which might be valid or not depending on the OP's use cases. – Matias Cicero Oct 15 '18 at 12:41

score 1 · Answer 2 · answered Oct 15 '18 at 12:37

1

If you want to keep all the digits you're entering you shouldn't convert your input into an int:

a=input('Enter a number: ') 
c=int(a[0])*3 
print(c)

If you enter 023 this returns 0.

answered Oct 15 '18 at 12:37

toti08

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score 1 · Answer 3 · answered Oct 15 '18 at 12:39

You can use a while loop to keep asking the user for digit-only input until the user enters one, and you should use the list() constructor to convert the digits to a list:

while True:
    a = input('Enter digits: ')
    if a.isdigit():
        break
    print('Please enter only digits.')
b=list(a)
c=int(b[0])*3
print(c)

Why won't Python store 0 in list?

3 Answers3