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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 add_chan_labels(self):
 """Add channel labels on the left."""

        window_start = self.parent.value('window_start')
        window_length = self.parent.value('window_length')
        label_width = window_length * self.parent.value('label_ratio')

        for row, one_label_item in enumerate(self.idx_label):
            self.scene.addItem(one_label_item)
            one_label_item.setPos(window_start - label_width,
                                  self.parent.value('y_distance') * row +
                                  self.parent.value('y_distance') / 2)