string - How to fix inconsistent return statement in python?

Question

I am new to python and i have this project I am working on a small project with two functions where the first returns the index of the first time a difference is spotted in a string. The next function does that but in a list of strings. Now, due to my being an amateur, i have used an excessive amount of if and else statements which resulted in too many return statements especially in the second function, and i get the error [R1710: inconsistent-return-statements]. How do i fix it and can anybody give me clear examples to better pieces of code? Sorry for the question being so long.

IDENTICAL = -1
def singleline_diff(line1, line2):
    """
    Inputs:
        line1 - first single line string
        line2 - second single line string
    Output:
        Returns the index where the first difference between
        line1 and line2 occurs.

        Returns IDENTICAL if the two lines are the same.
    """
    len1 = len(line1)
    len2 = len(line2)
    minimum_length = min(len1, len2)

    if len1 != len2:
        if minimum_length == 0:
            return 0
        for idx in range(minimum_length):
            if line1[idx] == line2[idx]:
                pass
            else:
                return idx
        return idx + 1

    for idx in range(len1):
        if line1[idx] == line2[idx]:
            pass
        else:
            return idx
    return IDENTICAL

def multiline_diff(lines1, lines2):
    """
    Inputs:
      lines1 - list of single line strings
      lines2 - list of single line strings
    Output:
      Returns a tuple containing the line number (starting from 0) and
      the index in that line where the first difference between lines1
      and lines2 occurs.

      Returns (IDENTICAL, IDENTICAL) if the two lists are the same.
    """
    line_no = singleline_diff(lines1, lines2)

    len_lines1, len_lines2 = len(lines1), len(lines2)

    if len_lines1 == len_lines2:

        if (len_lines1 or len_lines2) == 0:
            if len_lines1 == len_lines2:
                return (IDENTICAL, IDENTICAL)
            else:
                idx = singleline_diff(lines1[line_no], lines2[line_no])
                return (line_no, idx)

        else:
            idx = singleline_diff(lines1[line_no], lines2[line_no])

            if line_no == IDENTICAL:
                return (IDENTICAL, IDENTICAL)
            elif line_no != IDENTICAL:
                return (line_no, idx)

    else:
        return (line_no, 0)

Answer 1

Look at the code here:

if len_lines1 == len_lines2:
    return (IDENTICAL, IDENTICAL)
else:
    idx = singleline_diff(lines1[line_no], lines2[line_no])
    return (line_no, idx)

You could have written the above thing like:

if len_lines1 == len_lines2:
    return (IDENTICAL, IDENTICAL)
idx = singleline_diff(lines1[line_no], lines2[line_no])
return (line_no, idx)

You just don't need an else block to return this expression as this part of code will automatically be called if the control doesn't go into if block. Hope it helps.