PDDL Parser

Classical Planning in Python

PDDL Parser is a simple parser for PDDL, described in Python without external dependencies. It supports :strips, :negative-preconditions and :typing requirements. It contains a planner only as an example, being compact and readable for educational purposes. New features are outside the scope of this project, which was originally intended as a propositional PDDL parser to avoid the complexity of grounding and the ambiguity of typing descriptions.

PDDL Parser was originally designed and developed by Mau Magnaguagno in 2015 to be used in the classroom, following HyperTensioN's parsing style.

Source

• action.py with an Action class
• PDDL.py with a PDDL parser
• planner.py with a planner
• examples folder with PDDL domains:
  • Dinner from Daniel Weld, a propositional domain
  • Blocks World
  • Travelling Salesman Problem
  • Dock Worker Robot

Installation

The parser and planner can easily be used within other projects once installed. The examples and tests should work without installation.

cd pddl-parser
python setup.py install

Execution

The parser can be executed without planning, it outputs elements found in the input files and the structures created.

cd pddl-parser
python -B -m pddl_parser.PDDL examples/dinner/dinner.pddl examples/dinner/pb1.pddl

Parser output

----------------------------
['define',
 ['domain', 'dinner'],
 [':requirements', ':strips'],
 [':predicates', ['clean'], ['dinner'], ['quiet'], ['present'], ['garbage']],
 [':action', 'cook', ':precondition', ['clean'], ':effect', ['dinner']],
 [':action', 'wrap', ':precondition', ['quiet'], ':effect', ['present']],
 [':action',
  'carry',
  ':precondition',
  ['garbage'],
  ':effect',
  ['and', ['not', ['garbage']], ['not', ['clean']]]],
 [':action',
  'dolly',
  ':precondition',
  ['garbage'],
  ':effect',
  ['and', ['not', ['garbage']], ['not', ['quiet']]]]]
----------------------------
['define',
 ['problem', 'pb1'],
 [':domain', 'dinner'],
 [':init', ['garbage'], ['clean'], ['quiet']],
 [':goal', ['and', ['dinner'], ['present'], ['not', ['garbage']]]]]
----------------------------
Domain name: dinner
action: cook
  parameters: []
  positive_preconditions: [['clean']]
  negative_preconditions: []
  add_effects: [['dinner']]
  del_effects: []

action: wrap
  parameters: []
  positive_preconditions: [['quiet']]
  negative_preconditions: []
  add_effects: [['present']]
  del_effects: []

action: carry
  parameters: []
  positive_preconditions: [['garbage']]
  negative_preconditions: []
  add_effects: []
  del_effects: [['garbage'], ['clean']]

action: dolly
  parameters: []
  positive_preconditions: [['garbage']]
  negative_preconditions: []
  add_effects: []
  del_effects: [['garbage'], ['quiet']]

----------------------------
Problem name: pb1
Objects: {}
State: [['garbage'], ['clean'], ['quiet']]
Positive goals: [['dinner'], ['present']]
Negative goals: [['garbage']]

The planner uses BFS, it outputs the time taken and signatures of the actions in the plan found or failure. The output of the planner is more verbose with option -v.

cd pddl-parser
python -B -m pddl_parser.planner examples/dinner/dinner.pddl examples/dinner/pb1.pddl -v

Planner output

Time: 0.00200009346008s
plan:
action: cook
  parameters: []
  positive_preconditions: [['clean']]
  negative_preconditions: []
  add_effects: [['dinner']]
  del_effects: []

action: wrap
  parameters: []
  positive_preconditions: [['quiet']]
  negative_preconditions: []
  add_effects: [['present']]
  del_effects: []

action: carry
  parameters: []
  positive_preconditions: [['garbage']]
  negative_preconditions: []
  add_effects: []
  del_effects: [['garbage'], ['clean']]

API

Action

class Action:
    def __init__(self, name, parameters, positive_preconditions, negative_preconditions, add_effects, del_effects)
    def __str__(self)
    def __eq__(self, other)
    def groundify(self, objects, types)
    def replace(self, group, variables, assignment)

Parser

class PDDL_Parser:
    def scan_tokens(self, filename)
    def parse_domain(self, domain_filename, requirements=SUPPORTED_REQUIREMENTS)
    def parse_domain_extended(self, t, group)
    def parse_hierarchy(self, group, structure, name, redefine)
    def parse_objects(self, group, name)
    def parse_types(self, types)
    def parse_predicates(self, group)
    def parse_action(self, group)
    def parse_action_extended(self, action, group)
    def parse_problem(self, problem_filename)
    def parse_problem_extended(self, t, group)
    def split_predicates(self, group, positive, negative, name, part)

Planner

class PDDL_Planner:
    def solve(self, domain, problem)
    def applicable(self, state, positive, negative)
    def apply(self, state, positive, negative)

Extensions

New parser features should be added through inheritance using super and parse_*_extended methods. The Action class may also require modifications to deal with possible extensions.