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Mathematical Expression Parser and Evaluator

A zero-external-dependency mathematical expression parser, tokenizer, AST builder, and evaluator built from scratch in Python.

Features

  • Tokenizer: Converts input text strings into tokens (Numbers, Operators, Identifiers, Functions, Parentheses). Supports implicit multiplication (e.g. 2(3+4) or 3pi).
  • AST Parser: Recursive-descent parser building Abstract Syntax Trees respecting operator precedence and associativity (^, *, /, %, +, -).
  • Evaluator: Walks AST nodes safely to calculate results with variable binding support and builtin math functions (sin, cos, tan, sqrt, abs, log, exp, min, max, floor, ceil).
  • Interactive REPL & CLI: Support for interactive session and CLI expression evaluation.

Usage

CLI REPL

python expression_parser/main.py

Direct Expression Evaluation

python expression_parser/main.py "2 + 3 * (4 - 1)^2"
# Output: 29.0

Python API

from expression_parser import evaluate_expression

result = evaluate_expression("sin(pi / 2) + cos(0)")
print(result) # 2.0

vars_dict = {"x": 5, "y": 2}
res = evaluate_expression("x^2 + 2*x*y + y^2", vars_dict)
print(res) # 49.0