modeval
Modeval (or Modular Eval) is a modular and secure string evaluation library that can be used to create custom parsers or interpreters.
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)') )
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)
Super Technical Limitations
If you're planning on doing something crazy with this library, I'd read this.
Multi-character operators and functions are assigned unicode characters while being processed so there is a limit of around 4000 variables (and also a very high upper limit of functions). If this is a problem you can increase the offset of the function unicode character conversion. Decreasing the offset of the operators runs the risk of an operator getting translated into a regular number.
A possible fix for this is automatically allocating unicode characters based on the number of operators and variables but this is not implemented as of now.
147 Dec 1, 2022
10 Dec 13, 2022
1 Nov 3, 2021
4 Nov 28, 2021
3 Dec 18, 2021
1 Jan 5, 2022
1 Jan 24, 2022
1 Dec 11, 2021
3 Sep 12, 2022
6.9k Dec 27, 2022
7 Dec 16, 2022
1 Dec 21, 2021
2 Nov 13, 2021
1 Nov 02, 2021
1 Jan 10, 2022
19 Jun 03, 2021
5 Dec 20, 2022
2.9k Dec 29, 2022
9 Aug 16, 2022
5 Jun 28, 2022
253 Dec 14, 2022
2 Feb 04, 2022
4 Nov 14, 2022
97 Dec 07, 2022
8 Mar 11, 2022
2 Nov 01, 2021
0 Nov 05, 2021
3 Dec 28, 2022
1 Jan 09, 2022