expr.py

^{A safe and simple math evaluator for Python, built with rply.
View on PyPI}

Expr.py is a simple but safe math expression evaluator made for Python.
It can evaluate pretty advanced math concepts without crashing your computer.

Made using rply

Features

• Fully object oriented
• Completely typed for intellisense
• Protection against DoS attacks
• Customizable and extendable
• Follows order of operations
• Floating point precision

Getting started

You should install expr.py using pip:

$ pip install -U expr.py

Here is a simple program to get started:

import expr

if __name__ == '__main__':
    expression = '6 + 5 * 2' 
    print(expr.evaluate(expression))  # 16

What does expr.py support?

Basic operations

The following operations are supported by expr.py:

• + (addition)
• - (subtraction)
• * (multiplication)
• / (division)
• // (floor division)
• % (modulo)
• ^ (exponentation)
• ! (factorial)

Variables

The most basic way of defining variables is by passing in the variables kwarg into the evaluator.

expr.evaluate('2x', variables={'x': 2})  # 4

You can also let the input define variables:

expr.evaluate('x = 5')
expr.evaluate('6 + x')  # 11

There are by default, 2 predefined constants. (pi and e)

Functions [WIP]

You can define functions through the builtins kwarg:

def f(x):
    return x + 1

expr.evaluate('f(5)', builtins={'f': f})  # 6

You can also define functions via input:

expr.evaluate('f(x) = 2x')
expr.evaluate('f(3)')  # 6

There are a few builtin functions:

• sqrt
• cbrt
• log
• log10
• ln
• rad
• sin
• cos
• tan
• asin
• acos
• atan

Grouping

This concept is pretty simple, anything in parentheses will be evaluated before anything outside of them.

expr.evaluate('5 * 6 + 2')  # 32
expr.evaluate('5 * (6 + 2)')  # 40

States

You can create different states so that each can store their own variables and functions independently from others.

To do this, use expr.create_state:

state = expr.create_state()
print(state.evaluate('0.1 + 0.2'))  # 0.3 

Note: All parameters belong in create_state rather than in evaluate for states.

Again, variables and functions are independent from each other:

state1 = expr.create_state()
state1.evaluate('x = 1')

state2 = expr.create_state()
state2.evaluate('x')  # error (x is not defined)

state1.evaluate('x')  # 1

Changelog

v0.2

This update mainly brings bug fixes from v0.1.

What's new?

• You can now pass in custom classes into Parser.evaluate
• Constants are now precise to around 30 places.
• New constants (phi, tau)

More precise builtin functions

v0.2 changes the way some builtin functions are processed for boosts on both performance and precision.

• sqrt now uses Decimal.sqrt
• log10 now uses Decimal.log10
• ln now uses Decimal.ln
• cbrt now uses input ** expr.one_third
• sin now uses expr.sin
• cos now uses expr.cos

Bug fixes

• Fixed unary minus interfering with implicit multiplication.
  • in v0.1: 5-3 = -15
  • in v0.2: 5-3 = 2

Miscellaneous

• Many functions now have positional-only arguments for slight performance boosts
  • This drops support for Python 3.7
• Messages retrieved from ParsingError.friendly are now much more descriptive.

v0.3

What's new?

• Unary plus is now supported (E.g. +5)
• Scientific notation is now supported (E.g. 4E-2)
  • To reduce conflics, 'E' must be captialized.
    This means that 2e9 would evaluate to 2 * e * 9, for example.
• The cls kwarg is now supported in expr.evaluate

Bug fixes

• Catch OverflowError in the expr.Overflow parsing error.
• Fix invalid typings with Callable