class_docstr: Generic histogram class for real numbers
  
  Example:
  
      >>> h = Histogram(5)     # Initializing, bin width = 5
      >>> h << [2,3,2,7,8,5,5,0,7,9]     # Adding more items
      >>> print(h)
      N = 10, mean +- sd: 4.8000 +- 2.9740
      [ 0,  5): **** (4)
      [ 5, 10): ****** (6)
docstr: Initializes the histogram with the given data set.
  
  @param bin_width: the bin width of the histogram.
  @param data: the data set to be used. Must contain real numbers.
docstr_tok: ["Initializes","the","histogram","with","the","given","data","set",".","@","param","bin_width",":","the","bin","width","of","the","histogram",".","@","param","data",":","the","data","set","to","be","used",".","Must","contain","real","numbers","."]
code: def __init__(self, bin_width=1, data=None):
      """Initializes the histogram with the given data set.
  
      @param bin_width: the bin width of the histogram.
      @param data: the data set to be used. Must contain real numbers.
      """
      self._bin_width = float(bin_width)
      self._bins = None
      self._min, self._max = None, None
      self._running_mean = RunningMean()
      self.clear()
  
      if data:
          self.add_many(data)
  
imports: import math
label_desc: Use image node_id 1 to create a new Histogram object  with example: obj = Histogram(bin_width, data)