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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_field_description(f):
 """Get the type description of a GRPC Message field."""

    type_name = get_field_type(f)
    if type_name == 'MESSAGE' and \
            {sf.name for sf in f.message_type.fields} == {'key', 'value'}:
        return 'map<string, string>'
    elif type_name == 'MESSAGE':
        return f.message_type.full_name
    elif type_name == 'ENUM':
        return f.enum_type.full_name
    else:
        return type_name.lower()