old_contents: import matplotlib.pyplot as plot
  from line_2d import Line2D
  from helpers import if_string_convert_to_datetime
  
  class Hline(Line2D):
      def __init__(self, jsonDict):
          self.__dict__ = jsonDict
          self.xmin = if_string_convert_to_datetime(self.xmin)
          self.xmax = if_string_convert_to_datetime(self.xmax)
  
      def plot(self, axes):
          label = self.name if self.show_legend else ""
          plot.hlines(self.y,
                      self.xmin,
                      self.xmax,
                      color=self.color["value"],
                      lw=self.lineWidth,
                      linestyle=self.lineStyle,
                      alpha=self.alpha,
                    label=label)
          plot.hold(True)
new_contents: import matplotlib.pyplot as plot
  from line_2d import Line2D
  from helpers import if_string_convert_to_datetime
  
  class Hline(Line2D):
      def __init__(self, jsonDict):
          self.__dict__ = jsonDict
          self.xmin = if_string_convert_to_datetime(self.xmin)
          self.xmax = if_string_convert_to_datetime(self.xmax)
  
      def plot(self, axes):
          label = self.name if self.show_legend else ""
          plot.hlines(self.y,
                      self.xmin,
                      self.xmax,
                      color=self.color["value"],
                      lw=self.lineWidth,
                      linestyle=self.lineStyle,
                      alpha=self.alpha,
                      label=label)
  
subject: Update hline.py