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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 set_exposure_scale(self, name, scale=None):
 """Set the exposure correction of a source. Parameters name : str Source name. scale : factor Exposure scale factor (1.0 = nominal exposure). """

        name = self.roi.get_source_by_name(name).name
        if scale is None and name not in self._src_expscale:
            return
        elif scale is None:
            scale = self._src_expscale.get(name, 1.0)
        else:
            self._src_expscale[name] = scale
        self._scale_srcmap({name: scale})