simpleparser 0.1.2

Simple library with simple parser which parses simple expressions.

SimpleParser

Simple expressions parser.

Installing

Installing via pip:

$ pip install simpleparser

Usage

Parser

To just parse something, use Parser.parse method. With Parser you can describe different parsers. There is ready Default.parser.

from simpleparser import Defaults
expr = "a + b / 2"
parsed = Defaults.parser.parse(expr)
parsed(a=2, b=4) # returns 4.0

Parser.parse returns callable ParsedExpression object.

Custom parsers

Parser could be easily configured. It describes by set of operators and constants types (such numbers or booleans). See documentation for Operator and ConstantType below.

from simpleparser import Parser, Defaults
my_parser = Parser(
    operators=[Defaults.plus, Defaults.minus, Defaults.mul, Defaults.div], # using some operators from `Defaults` here
    constants=[Defaults.integers_decimal, Defaults.float_point]
)

my_parser here parses simple math expressions with 4 basic operators and decimal numbers, for example 1 + 2.0 * a.

Operator

Creating custom operator:

from simpleparser import Operator, Parser
in_op = Operator(
    name="in",
    operator_type=2,
    func=lambda el, container: el in container,
    signs=("\u2208",),
    priority=3,
)
# creating new parser which uses this operator
new_parser = Parser([in_op], [])
el_in_set_checker = new_parser.parse("a in A")
el_in_set_checker(a=1, A={1, 2, 3}) # True
el_in_set_checker(a=0, A={1, 2, 3}) # False

ConstantType

Describes type of constant which can be use in expression. Here is realisation of Defaults.boolean:

from simpleparser import ConstantType
boolean = ConstantType(r"(True|False|true|false)$", lambda s: True if s in {"True", "true"} else False)

Parser with that constant type replaces words which matched by boolean's regular expression to True or False.

parser = Parser([],[boolean])
parser.parse("True")() # True
parser.parse("false")() # False