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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 _mark_dirty(self, xblock, value):
 """Set this field to dirty on the xblock."""

        # pylint: disable=protected-access

        # Deep copy the value being marked as dirty, so that there
        # is a baseline to check against when saving later
        if self not in xblock._dirty_fields:
            xblock._dirty_fields[self] = copy.deepcopy(value)