sexpy — S-expression manipulation toolkit

sexpy contains some tools to allow effortless manipulation of data encoded as S-expressions. Its goal is to wrap commonly-used operations into a reusable package, allowing S-expressions to be implemented quickly into any project. Providing comprehensive, powerful set of functionalities is outside the scope of this project.

In particular, sexpy aids in the transformation between these three levels of abstraction:

Plain text ⟷ Nested lists ¹⟷ Python data types

1. Still WIP.

Example

#
# Example PDDL problem parsing and destructuring
#

import sexpy
import sexpy.schema as sxs

# The source code to parse
src = '''
(define
    (problem BLOCKS-4-1)
    (:domain blocks)
    (:objects A C D B - block)
    (:init 
        (clear B)
        (ontable D) 
        (on B C) 
        (on C A) 
        (on A D) 
        (handempty))
    (:goal (and (on D C) 
                (on C A) 
                (on A B))))
'''

# An schema describing the source layout (using shorthand syntax)
pddl_problem = sxs.desugar(
    sxs.Dict(
        sxs.Ignore('define'),
        ('problem',      sxs.Atom),
        [sxs.Either(
            (':domain',  sxs.Atom),
            (':objects', [sxs.Atom]),
            (':init',    [([sxs.Any])]),
            (':goal',    sxs.Any),
        )]
    )
)

# Parse the source string into nested lists
sexpr = sexpy.loads(src)
print(f'{sexpr = }')

# Validate and destructure the nested lists according to the schema
output = pddl_problem.extract(sexpr[0])
print(f'{output = }')

# Or both at the same time:
output = sexpy.loads(src, schema=pddl_problem)
print(f'{output = }')