class_docstr: A representation of a mathematical relationship, a node in a program.
  
  This object is able to be called with NumPy vectorized arguments and return
  a resulting vector based on a mathematical relationship.
  
  Parameters
  ----------
  function : callable
      A function with signature function(x1, *args) that returns a Numpy
      array of the same shape as its arguments.
  
  name : str
      The name for the function as it should be represented in the program
      and its visualizations.
  
  arity : int
      The number of arguments that the ``function`` takes.
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code: def __init__(self, function, name, arity):
      self.function = function
      self.name = name
      self.arity = arity
  
file_path: gplearn/gplearn/functions.py
imports: import numpy
  from joblib import wrap_non_picklable_objects
label_desc: Use image node_id 1 to create a new _Function object from inherited base classes: object with example: obj = _Function(function, name, arity)