def strip_str(inp):
    """Helper method to strip a string of all non alphanumeric characters.

    Args:
        inp (str): -

    Returns:
        str: stripped output

    >>> x = 'Test-string123__:'
    >>> y = strip_str(x)
    >>> y
    'teststring123'
    """

    return ''.join(ch.lower() for ch in inp if ch.isalnum())