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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 update_margins(self):
 """Update plugin margins"""

        layout = self.layout()
        if self.default_margins is None:
            self.default_margins = layout.getContentsMargins()
        if CONF.get('main', 'use_custom_margin'):
            margin = CONF.get('main', 'custom_margin')
            layout.setContentsMargins(*[margin]*4)
        else:
            layout.setContentsMargins(*self.default_margins)