developer_api.md

The Developer API

A Simple Demo

Parser definition methods

• customize()
• add_operator(operator_symbol, num_args, left_right_assoc, operator_function)
• add_variable(variable, value)
• add_function(function_name, num_args, function_method)
  • if a function can accept any number of arguments, pass ... for the num_args argument (see the hypot function)
  • if a function can accept different numbers of arguments, pass a tuple of all possible numbers of arguments a function can have for the num_args argument (see the log function)

Parser parse/evaluation methods

• parse(expression)
• evaluate(expression)
• vars()

Parser attributes

• LEFT and RIGHT
• MAX_VARS
• ident_letters
• user_defined_functions_supported

Usage Notes

Creating a custom ArithmeticParser class

Defining a new variable

Adding a new operator

Adding a new function

Accessing evaluated results and variables from your code:

parser['xyz'] = 100
parser.evaluate("√xyz") # Returns 10.0

Defining an operator that is both unary and binary

SECURITY WARNINGS

• Do not add functions that use or give access to eval, exec, compile, import, subprocess or os
• If adding functions that start separate threads, limit the total number of threads that your parser will create at one time.
• Be extremely careful if reading/writing to the file system
• Take care when exposing access to an underlying database or server files
• Some math functions may need to be constrained to avoid extended arithmetic processing (see constrained_factorial in the BaseArithmeticParser as an example)
• When populating web page elements with gathered input strings, be sure to escape potential quotation and control characters (see bottle_repl.py as an example)
• Be aware that your functions may get called recursively, or in an endless loop