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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 _only_shifts(self, modifiers):
 """Check if modifiers pressed are only shifts"""

        if not modifiers or len(modifiers) > 2:
            return False
        if len(modifiers) == 2:
            return 'left shift' in modifiers and 'right shift' in modifiers
        if len(modifiers) == 1:
            return 'left shift' in modifiers or 'right shift' in modifiers