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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 validlocations(configuration=None):
 # type: () -> List[Dict] """ Read valid locations from HDX Args: configuration (Optional[Configuration]):
 HDX configuration. Defaults to global configuration. Returns: List[Dict]: A list of valid locations """

        if Locations._validlocations is None:
            if configuration is None:
                configuration = Configuration.read()
            Locations._validlocations = configuration.call_remoteckan('group_list', {'all_fields': True})
        return Locations._validlocations