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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_populate_from_value(self, instance):
 """Get the value from ``populate_from`` attribute."""

        if hasattr(self.populate_from, '__call__'):
            # ResolweSlugField(populate_from=lambda instance: ...)
            return self.populate_from(instance)
        else:
            # ResolweSlugField(populate_from='foo')
            attr = getattr(instance, self.populate_from)
            return attr() if callable(attr) else attr