math-trees

Use Python to create and evaluate parse trees for simple algebraic expressions.

Prerequisites

This software works in both Python 2.7 and Python 3.

Usage

To use the library, simply import the main Python file with import expressionparse

To parse an expression, create a new Tree object and use its parse() method:

import expressionparse

expression = 'x+y'

t = expressionparse.Tree()
t.parse(expression)

The software is currently only capable of parsing expressions written using infix notation and containing only the +,-,*,/,^, and ! operations.

Output

Once an expression has been parsed, various output options are available (all return strings):

• Polish Notation (Tree.toPolishNotation)
• Infix Notation (Tree.toInfixNotation)
• Reverse Polish Notation (Tree.toReversePolishNotation)

    >>> t = expressionparse.Tree()
    >>> t.parse('2*2+1')
    >>> print t.toPolishNotation()
    
    + * 2 2 1
    
    >>> print t.toInfixNotation()
    
    2 * 2 + 1
    
    >>> print t.toReversePolishNotation()
    
    2 2 * 1 +

Trees and nodes can also be stringified using the str() operator. This will output using infix notation but with explicit delineation of the various nodes using square brackets.

    >>> t = expressionparse.Tree()
    >>> t.parse('2*2+1')
    >>> print t
    
    [ [ 2 * 2 ] + 1 ]

Evaluating Expressions

Expressions containing only numbers can be evaluated using the Tree.evaluate method. If an error is encountered during evaluation, an EvalException will be raised.

    >>> t = expressionparse.Tree()
    >>> t.parse('1+2')
    >>> print t.evaluate()
    
    3.0

Variables

The math-trees library can parse expressions containing variables with single-character names, e.g. 'x' or 'y'.

Expressions containing variables cannot be evaluated unless the values of all variables have been set using the Tree.setVariable method.

    >>> t = expressionparse.Tree()
    >>> t.parse('x+2')
    >>> t.setVariable('x',1)
    >>> print t.evaluate()
    
    3.0