Python Mathematical Expression Evaluator

Based on js-expression-eval, by Matthew Crumley (email@matthewcrumley.com, http://silentmatt.com/) https://github.com/silentmatt/js-expression-eval

Ported to Python and modified by Vera Mazhuga (ctrl-alt-delete@live.com, http://vero4ka.info/)

You are free to use and modify this code in anyway you find useful. Please leave this comment in the code to acknowledge its original source. If you feel like it, I enjoy hearing about projects that use my code, but don't feel like you have to let me know or ask permission.

Installation

pip install py_expression_eval

Tests

python setup.py test

Documentation

All the classes and methods of py-expression-eval were written as similar as possible to their analogues from js-expression-eval to make it easier to use for validation on back-end side.

Parser

Parser is the main class of the library that contains the methods to parse, evaluate and simplify mathematical expressions. In order to use the library you need to create an instance of this class:

> from py_expression_eval import Parser
> parser = Parser()

Once you instantiated Parser class, you can create Expression object using parse method:

> parser.parse('2 * 3')
Out: <py_expression_eval.Expression instance at 0x7f40cc4e5ef0>

Parser.Expression

evaluate() takes a dictionary with variables as a parameter and returns the value of the expression:

> parser.parse('2 * 3').evaluate({})
Out: 6
> parser.parse('2 * 3.0').evaluate({})
Out: 6.0
> parser.parse('2 * x').evaluate({'x': 7})
Out: 14
> parser.parse('2 * x').evaluate({'x': 7.0})
Out: 14.0

substitute() creates a new expression where specified variables are replaces with a new expression. For example, to replace x with 3 + x in 2 * x expression we use the following code:

> parser.parse('2 * x').substitute('x', '3 + x').toString()
Out: '(2*(3+x))'

variables() returns a list of the variables for the expression:

> parser.parse('2 * x + y').variables()
Out: ['x', 'y']

simplify() simplifies the expression. For example,

> parser.parse('2 * 3 * x + y').simplify({}).toString()
Out: '((6*x)+y)'
> parser.parse('2 * 3 * x + y').simplify({'x': -1}).toString()
Out: '(-6+y)'
> parser.parse('cos(PI) + x').simplify({}).toString()
Out: '(-1.0+x)'

toString() converts the expression to a string.

Available operators, constants and functions

Examples

from py_expression_eval import Parser

parser = Parser()
parser.parse('2 * 3').evaluate({})  # 6
parser.parse('2 ^ x').evaluate({'x': 3})  # 8.0
parser.parse('2 * x + 1').evaluate({'x': 3})  # 7
parser.parse('2 + 3 * x').evaluate({'x': 4})  # 14
parser.parse('(2 + 3) * x').evaluate({'x': 4}) # 20
parser.parse('2-3^x').evaluate({'x': 4})  # -79.0
parser.parse('-2-3^x').evaluate({'x': 4})  # -83.0
parser.parse('-3^x').evaluate({'x': 4})  # -81.0
parser.parse('(-3)^x').evaluate({'x': 4})  # 81.0
parser.parse('2*x + y').evaluate({'x': 4, 'y': 1})  # 9
parser.parse('round(log(2.7))').evaluate({}) # 1.0

# substitute
expr = parser.parse('2 * x + 1')
expr2 = expr.substitute('x', '4 * x')  # ((2*(4*x))+1)
expr2.evaluate({'x': 3})  # 25

# simplify
expr = parser.parse('x * (y * atan(1))').simplify({'y': 4})
expr.toString()  # x*3.141592
expr.evaluate({'x': 2})  # 6.283185307179586

# get variables
expr = parser.parse('x * (y * atan(1))')
expr.variables()  # ['x', 'y']
expr.simplify({'y': 4}).variables()  # ['x']

Available operations

from py_expression_eval import Parser

parser = Parser()
parser.parse('2 + 3').evaluate({})  # 5
parser.parse('2 - 3').evaluate({})  # -1
parser.parse('2 * 3').evaluate({})  # 6
parser.parse('2 / 3').evaluate({})  # 0.6666666666666666
parser.parse('2 % 3').evaluate({})  # 2
parser.parse('-2').evaluate({})  # -2
parser.parse('abs(-2)').evaluate({}) # 2

parser.parse('ceil(1.4)').evaluate({})  # 2.0
parser.parse('floor(1.4)').evaluate({})  # 1.0
parser.parse('round(1.4)').evaluate({})  # 1.0

parser.parse('2^3').evaluate({})  # 8.0
parser.parse('sqrt(16)').evaluate({}) # 4.0

parser.parse('sin(3.14)').evaluate({})  # 0.0015926529164868282
parser.parse('cos(3.14)').evaluate({})  # -0.9999987317275395
parser.parse('tan(3.14)').evaluate({})  # -0.0015926549364072232

parser.parse('asin(1)').evaluate({})  # 1.5707963267948966
parser.parse('acos(1)').evaluate({})  # 0.0
parser.parse('atan(1)').evaluate({})  # 0.7853981633974483

parser.parse('log(2.7)').evaluate({})  # 0.9932517730102834
parser.parse('exp(1)').evaluate({})  # 2.718281828459045

parser.parse('log(E)').evaluate({})  # 1.0
parser.parse('cos(PI)').evaluate({})  # -1.0

parser.parse('x||y').evaluate({'x': 2, 'y': 3})  # '23'

parser.parse('num in (1,2,3)').evaluate({'num': 1})  # True
parser.parse('"word" in "word in sentence"').evaluate({})  # True

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