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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def parse_string(str_, validate=False):
 """ Tries to parse a given string into a Bibliography instance. If ``validate`` is passed as keyword argument and set to ``True``, the Bibliography will be validated using the standard rules. """

    result = pattern.parseString(str_)[0]
    if validate:
        result.validate()
    return result