Return the number of differences betweeen 2 peptides

    :param str p1: Peptide 1
    :param str p2: Peptide 2
    :return: The number of differences between the pepetides
    :rtype: int

    >>> pept_diff('ABCDE', 'ABCDF')
    1
    >>> pept_diff('ABCDE', 'ABDFE')
    2
    >>> pept_diff('ABCDE', 'EDCBA')
    4
    >>> pept_diff('ABCDE', 'ABCDE')
    0

def pept_diff(p1, p2):
    """
    Return the number of differences betweeen 2 peptides

    :param str p1: Peptide 1
    :param str p2: Peptide 2
    :return: The number of differences between the pepetides
    :rtype: int

    >>> pept_diff('ABCDE', 'ABCDF')
    1
    >>> pept_diff('ABCDE', 'ABDFE')
    2
    >>> pept_diff('ABCDE', 'EDCBA')
    4
    >>> pept_diff('ABCDE', 'ABCDE')
    0
    """
    if len(p1) != len(p2):
        return -1
    else:
        return sum([p1[i] != p2[i] for i in range(len(p1))])