class_docstr: The Slope filter calculates the slope of a least-squares regression line.
  
  :param dataSeries: The DataSeries instance being filtered.
  :type dataSeries: :class:`pyalgotrade.dataseries.DataSeries`.
  :param period: The number of values to use to calculate the slope.
  :type period: int.
  :param maxLen: The maximum number of values to hold.
      Once a bounded length is full, when new items are added, a corresponding number of items are discarded from the
      opposite end. If None then dataseries.DEFAULT_MAX_LEN is used.
  :type maxLen: int.
  
  .. note::
      This filter ignores the time elapsed between the different values.
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code: def __init__(self, dataSeries, period, maxLen=None):
      super(Slope, self).__init__(
          dataSeries, SlopeEventWindow(period), maxLen
      )
  
imports: from pyalgotrade import technical
  from pyalgotrade.utils import collections
  from pyalgotrade.utils import dt
  import numpy
  from scipy import stats
label_desc: Use image node_id 1 to create a new Slope object from inherited base classes: technical with example: obj = Slope(dataSeries, period, maxLen)