In Python, I often use local variables in defining functions, like so:

def f(x):
   k = initialk
   < 'do something to k' >

I would like to do something similar in Mathematica for instance, I would want:


to return $(\cdots((x^2+1)^2+1)^2+\cdots1)^2$.

How does one ordinarily do this in Mathematica?

  • 1
    $\begingroup$ Module, With, or Block will do what you're looking for. $\endgroup$
    – Carl Lange
    Commented Mar 8, 2020 at 18:23
  • $\begingroup$ Don’t try to program in Mathematica by reproducing Python practices. You will write inefficient code and end up very frustrated. $\endgroup$
    – MarcoB
    Commented Mar 9, 2020 at 2:47
  • 1
    $\begingroup$ @MarcoB Is there a "Good Coding Practices for Mathematica" somewhere that I could refer to? $\endgroup$
    – R. Burton
    Commented Mar 9, 2020 at 19:25
  • $\begingroup$ @R.Burton if you asked that as a question, I think you would get some pointers to suitable material. $\endgroup$
    – mikado
    Commented Mar 9, 2020 at 21:18
  • $\begingroup$ @R.Burton For a start, see Where can I find examples of good Mathematica programming practice? $\endgroup$
    – MarcoB
    Commented Mar 9, 2020 at 22:16

1 Answer 1


If you want, you could write some thing like this

f[x_] := Module[{k = x},
  Do[k = k^2 + 1, {i, 0, x - 1}];

A more natural form would be

f[x_] := Nest[#^2 + 1 &, x, x]

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