Programmer's Notepad - Calculator Part 2

This time we’re going to use a PyPN script to evaluate maths expressions. We’re cheating a little, because we’re just going to ask python to evaluate a string and get a number back out.

[sourcecode language=”python”] import pn, scintilla

@script(“Calculator”) def DoMaths(): s = scintilla.Scintilla(pn.CurrentDoc())

if s.SelectionEnd - s.SelectionStart < 1:

sel = s.SelText

i = eval(sel)
if type(i) in [int, float, complex]:
    pn.AddOutput(str(i)) [/sourcecode]

To use this, simply select an expression like “5+5” in the editor, run the script, and the output window will contain the evaluation of the expression.

This script is very simple, and in fact could be generalised to a python expression evaluator, but it serves the intended purpose well. It could also be adapted to make sure that expressions are of the form “exp=” and then put the result after the = sign, or perhaps to replace the selected expression with the result. These changes are left as exercises for the reader!