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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 modSymbolsFromLabelInfo(labelDescriptor):
 """Returns a set of all modiciation symbols which were used in the labelDescriptor :param labelDescriptor: :class:`LabelDescriptor` describes the label setup of an experiment :returns: #TODO: docstring """

    modSymbols = set()
    for labelStateEntry in viewvalues(labelDescriptor.labels):
        for labelPositionEntry in viewvalues(labelStateEntry['aminoAcidLabels']):
            for modSymbol in aux.toList(labelPositionEntry):
                if modSymbol != '':
                    modSymbols.add(modSymbol)
    return modSymbols