def idf(x):
  """
  Returns the identity function. 
  
  The identity function returns the element with which the function was applied. 
  
  .. note:: Useful commonly as an identity element of a function composition. 

  Parameters
  ----------  
  x : any
    Element to apply the function with.

  Returns
  -------
  x : any
    The same element as `x`.
  
  Examples
  --------
  
  >>> idf(1)
  1
  >>> idf([])
  []
  """  
  return x