What causes 'valueerror: invalid literal for int() with base 10' in python?

This error arises when attempting to convert a string to an integer, but the string doesn't represent a valid integer.

Example:

num = int("abc")

Solution:

try:
    num = int("123")
except ValueError:
    print("Not a valid integer string.")

Always validate string content before converting to integers or handle the exception gracefully.