code: def finite_diff(expression, variable, increment=1):
      """
      Takes as input a polynomial expression and the variable used to construct
      it and returns the difference between function's value when the input is
      incremented to 1 and the original function value. If you want an increment
      other than one supply it as a third argument.
  
      Examples
      ========
  
      >>> from sympy.abc import x, y, z
      >>> from sympy.series.kauers import finite_diff
      >>> finite_diff(x**2, x)
      2*x + 1
      >>> finite_diff(y**3 + 2*y**2 + 3*y + 4, y)
      3*y**2 + 7*y + 6
      >>> finite_diff(x**2 + 3*x + 8, x, 2)
      4*x + 10
      >>> finite_diff(z**3 + 8*z, z, 3)
      9*z**2 + 27*z + 51
      """
      expression = expression.expand()
      expression2 = expression.subs(variable, variable + increment)
      expression2 = expression2.expand()
      return expression2 - expression
  
label_desc: Use image node_id 1 for calling a global function with example usage: finite_diff(expression, variable, increment) and returns: unknown