class_docstr: Computes the difference between the value in a list and the
  previous value in that list.
  
  Args:
      periods (int): The number of periods by which to shift the index row.
          Default is 0. Periods correspond to rows.
  
  Description:
      Given a list of values, compute the difference from the previous
      item in the list. The result for the first element of the list will
      always be `NaN`.
  
  Examples:
      >>> diff = Diff()
      >>> values = [1, 10, 3, 4, 15]
      >>> diff(values).tolist()
      [nan, 9.0, -7.0, 1.0, 11.0]
  
      You can specify the number of periods to shift the values
  
      >>> values = [1, 2, 4, 7, 11, 16]
      >>> diff_periods = Diff(periods = 1)
      >>> diff_periods(values).tolist()
      [nan, nan, 1.0, 2.0, 3.0, 4.0]
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code: def __init__(self, periods=0):
      self.periods = periods
  
imports: from woodwork.column_schema import ColumnSchema
  from featuretools.primitives.base import TransformPrimitive
label_desc: Use image node_id 1 to create a new Diff object from inherited base classes: TransformPrimitive with example: obj = Diff(periods)