Replace contents with 'xxx' to prevent syntax matching.

    >>> mute_string('"abc"')
    '"xxx"'
    >>> mute_string("'''abc'''")
    "'''xxx'''"
    >>> mute_string("r'abc'")
    "r'xxx'"

def mute_string(text):
    """
    Replace contents with 'xxx' to prevent syntax matching.

    >>> mute_string('"abc"')
    '"xxx"'
    >>> mute_string("'''abc'''")
    "'''xxx'''"
    >>> mute_string("r'abc'")
    "r'xxx'"
    """
    start = 1
    end = len(text) - 1
    # String modifiers (e.g. u or r)
    if text.endswith('"'):
        start += text.index('"')
    elif text.endswith("'"):
        start += text.index("'")
    # Triple quotes
    if text.endswith('"""') or text.endswith("'''"):
        start += 2
        end -= 2
    return text[:start] + 'x' * (end - start) + text[end:]