A very simple calculator based on a recursive descent parser (not
using python eval)
Supports exponentiation, add, sub, mul, div, modulo/formatting, shift, bitwise and/or/xor, comparison operators, logical and/or (short-circuited), unary negation, parenthesized subexpressions and assignment (an operator like in C, not a statement like in Python).
Atoms can be integers, floats, strings or variables.
It's also possible to store an expression in a variable (like a spreadsheet
formula) using the := operator. No check about circular formulas is present.
The core parser/evaluator is about 40 lines. The whole program is less than 100 lines in total.
Works in both Python 2.x and 3.x
Example session:
> 1 + 1
2
> 1 + 2*3
7
> 1 + 2*(3 + 4)
15
> pi = 3.141592654
3.141592654
> r = 10
10
> r * r * pi
314.1592654
> area := r * r * pi
314.1592654
> r = 100
100
> area
31415.92654
> r =42
42
> area
5541.76944166