"invalid literal for int() with base 10:" What does this actually mean?

Question

Beginner here! I am writing a simple code to count how many times an item shows up in a list (ex. count([1, 3, 1, 4, 1, 5], 1) would return 3).

This is what I originally had:

def count(sequence, item):
    s = 0
    for i in sequence:
       if int(i) == int(item):
           s += 1
    return s

Every time I submitted this code, I got

"invalid literal for int() with base 10:"

I've since figured out that the correct code is:

def count(sequence, item):
    s = 0
    for i in sequence:
       if **i == item**:
           s += 1
    return s

However, I'm just curious as to what that error statement means. Why can't I just leave in int()?

Answer 1

The error is "invalid literal for int() with base 10:". This just means that the argument that you passed to int doesn't look like a number. In other words it's either empty, or has a character in it other than a digit.

This can be reproduced in a python shell.

>>> int("x")
ValueError: invalid literal for int() with base 10: 'x'