pratt-calc 0.2.2

Arithmetic calculator which uses a Pratt parser

Introduction

An arithmetic expression calculator in Python, demoing the Pratt parsing algorithm.

This takes inspiration from this 2010 blog post by Eli Bendersky, as well as a few other sources:

1. Simple but Powerful Pratt Parsing
2. Pratt Parsers: Expression Parsing Made Easy
3. Compiling Expressions (Chapter 17 of Crafting Interpreters)

Requirements

Requires Python 3.13 or greater.

Installation

pipx install pratt-calc

In some cases it may be necessary to specify the Python version manually:

PIPX_DEFAULT_PYTHON=python3.13 pipx install pratt-calc

Or, if you have uv installed:

uvx pipx install pratt-calc

Contributing

Install uv, then run:

git clone https://github.com/BrandonIrizarry/pratt-calc
cd pratt-calc
uv sync --locked

Usage

pratt-calc $EXPRESSION

Example:

pratt-calc '3-4*5'

This should print -17 at the console.

Note that surrounding the input with single-quotes is recommended for all but the simplest expressions, to avoid clashing with the shell you're using.

Trigonometric Functions

pratt-calc supports the following trigonometric functions:

1. sin
2. cos
3. tan
4. csc
5. sec
6. cot

The constant 𝝿 is also available as pi. Examples:

pratt-calc 'cos(pi)' => -1.0

pratt-calc 'sin(1)^2 + cos(1)^2' => 1.0

A Note on the Implementation of Trig Functions

Trig functions are implemented as unary operators, as opposed to function calls. Hence the parentheses used by sin and so forth are merely there to enforce precedence, even though they conveniently evoke the intuition of a function call.