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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 get_scanner (type, prop_set):
 """ Returns a scanner instance appropriate to 'type' and 'property_set'. """

    if __debug__:
        from .property_set import PropertySet
        assert isinstance(type, basestring)
        assert isinstance(prop_set, PropertySet)
    if registered (type):
        scanner_type = __types [type]['scanner']
        if scanner_type:
            return scanner.get (scanner_type, prop_set.raw ())
            pass

    return None