'Gets the build setting for key.
All child XCConfiguration objects must have the same value set for the
setting, or a ValueError will be raised.'

def GetBuildSetting(self, key):

    value = None
    for configuration in self._properties['buildConfigurations']:
        configuration_value = configuration.GetBuildSetting(key)
        if (value is None):
            value = configuration_value
        elif (value != configuration_value):
            raise ValueError(('Variant    values    for    ' + key))
    return value
