Skip to main content

Pure Python math evaluater without using eval() and no dependencies.

Project description

modeval

Modeval (or Modular Eval) is a modular and secure string evaluation library that can be used to create custom parsers or interpreters.

Install using: pip install modeval

Basic Use

from modeval import Parser

# Create a new parser with the default ruleset.
p = Parser()

# Evalute string. Spaces are automatically removed.
print( p.eval('1 * (2-3)') )

Because spaces are removed, 1 3 + 2 is parsed as 13+2.

Rulesets

The Parser class will use a basic mathematical ruleset if no specific ruleset is specified. Use the default ruleset as a guide on how to make custom ones.

from modeval import Parser, Ruleset

import operator # (standard library)

default_ruleset = Ruleset()

# Notice the order of the array follows order of operations.
default_ruleset.operators = [
    [('^', operator.pow), ('**', operator.pow)],
    [('*', operator.mul), ('/', operator.truediv)],
    [('+', operator.add), ('-', operator.sub)]
]

p = Parser(ruleset = default_ruleset)

Operator behavior is defined by the function attached to the sign/symbol in the tuple.

Note that the attached methods must have two inputs in the correct order (L + R is parsed as add(L, R)).

Modeval also supports functions like sin(), but they are not included in the default ruleset. To add them, reference the following:

from modeval import Parser, Ruleset

import math # (standard library)

custom_ruleset = Ruleset()

# Function order does not matter, so an extra layer of grouping is not needed.
custom_ruleset.functions = [
    ('sin', math.sin),
    ('cos', math.cos),
    ('tan', math.tan)
]

p = Parser(ruleset = custom_ruleset)
# You can now use "sin(...)" in the input string for eval().

Speaking of sin(), what about pi? Modeval also supports custom variables. They can be set like this:

from modeval import Parser, Ruleset

import math # (standard library)

custom_ruleset = Ruleset()

custom_ruleset.variables = [
    ('pi', math.pi) # Keep in mind this needs to be a value and not a function.
]

p = Parser(ruleset = custom_ruleset)
# Now you can use pi as you would expect (pi*3/2)

Technical Limitations

If you're planning on doing something crazy with this library, I'd read this.

Mult-character operators/variables/functions are assigned unique single unicode characters, meaning there is a limit for the amount of each you can have (around 4000 for each). This shouldn't be a problem in most cases.

A possible fix for this is dynamically allocating unicode characters, but this is not implemented yet.

Project details


Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution

modeval-1.1.tar.gz (5.2 kB view hashes)

Uploaded Source

Supported by

AWS AWS Cloud computing and Security Sponsor Datadog Datadog Monitoring Fastly Fastly CDN Google Google Download Analytics Microsoft Microsoft PSF Sponsor Pingdom Pingdom Monitoring Sentry Sentry Error logging StatusPage StatusPage Status page