Python word checker

Question

emp = []

def run(first, second):
     front_index = 0
     back_index = 0
     if len(first) > len(second):
         front = second
         back = first
         num = first_bigger_than_second(front, back)
         return num
     elif len(first) < len(second):
         front = first
         back = second
         break
     else:
         front = second
         back = first
         break

def first_bigger_than_second(first, back):
    first_index = 0
    back_index = 0
    print(len(first))
    print(len(back))
    while first_index < len(first) and back_index < len(back):
        if first[first_index] == back[back_index] and back_index == len(back):
            print("first", first)
            print("first_index", first_index)
            print("first[first_index]", first[first_index])
            print("back", back)
            print("back_index", back_index)
            print("back[back_index]", back[back_index])
            emp.append(back[back_index])
            first_index += 1
            back_index = 0
            print(1)
        elif first[first_index] == back[back_index]:
            print("first", first)
            print("first_index", first_index)
            print("first[first_index]", first[first_index])
            print("back", back)
            print("back_index", back_index)
            print("back[back_index]", back[back_index])
            emp.append(back[back_index])
            back_index += 1
            print(2)
        elif back_index == len(back) - 1:
            print("first", first)
            print("first_index", first_index)
            print("first[first_index]", first[first_index])
            print("back", back)
            print("back_index", back_index)
            print("back[back_index]", back[back_index])
            first_index += 1
            back_index = 0
            print(3)
        else:
            print("first", first)
            print("first_index", first_index)
            print("first[first_index]", first[first_index])
            print("back", back)
            print("back_index", back_index)
            print("back[back_index]", back[back_index])
            back_index += 1
            print(4)

num1 = 0plm1qaz
num2 = 1qaz0pl
run(num1, num2)
print(emp)
"""

All the print functions are used to trace with if loop is been executed

The problem is when I print the emp, the output is ["1", "q", "a", "z"] expected output is: ["1", "q", "a", "z", "0", "p", "l"].

The code compares two word user inputs and returns the same word. Example: When you input "2aba" and "2ac" , it will give a result as ["2", "a", "a"] since the code is work like the "2" from the "2aba" compare with "2ac" and the "a" from the "2aba" is compared again with "2ac" and "b" from the "2aba" is compared with "2ac" and "a" from the "2aba" compare with "2ac"

Answer 1

break in your run() raises SyntaxError as there is no loop. After removing it, your code can run but it is not giving you expected result.

When first_index = 3 (z in num2), back_index = 7 (z in num1), the second elif statement runs, back_index + 1 = 8 == len(num1), while loop break and you get the result ["1", "q", "a", "z"]. Although you put the first and third if statement to reset the back_index, the first one never run as the while loop already break and the third one will not run as the second one runs.

We can use in to check if a character of a word exist in another word.

def same_chars(first,second):
    # use the shorter one as first
    if len(first) > len(second):
        first, second = second, first
    emp = [chars for chars in first if chars in second]
    return emp

num1 = "0plm1qaz"
num2 = "1qaz0pl"
print(same_chars(num1, num2))

Output:

['1', 'q', 'a', 'z', '0', 'p', 'l']