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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 from_string(cls, s, name=None, modules=None, active=None):
 """ Instantiate a REPP from a string. Args: name (str, optional):
 the name of the REPP module modules (dict, optional):
 a mapping from identifiers to REPP modules active (iterable, optional):
 an iterable of default module activations """

        r = cls(name=name, modules=modules, active=active)
        _parse_repp(s.splitlines(), r, None)
        return r