OptaPy
OptaPy is an AI constraint solver for Python to optimize the Vehicle Routing Problem, Employee Rostering, Maintenance Scheduling, Task Assignment, School Timetabling, Cloud Optimization, Conference Scheduling, Job Shop Scheduling, Bin Packing and many more planning problems.
OptaPy wraps the OptaPlanner engine internally, but using OptaPy in Python is significantly slower than using OptaPlanner in Java or Kotlin.
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Warning
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OptaPy is an experimental technology. It is at least 20 times slower than using OptaPlanner in Java or Kotlin. |
Get started
Prerequisites
-
Install JDK 11 or later with the environment variable
JAVA_HOMEconfigured to the JDK installation directory.
Installing
pip install optapy
Source code overview
Domain
In OptaPy, the domain has three parts:
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Problem Facts, which do not change
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Planning Entities, which have one or more planning variables
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Planning Solution, which define the facts and entities of the problem
Problem Facts
To declare Problem Facts, use the @problem_fact decorator
from optapy import problem_fact
@problem_fact
class Timeslot:
def __init__(self, id, day_of_week, start_time, end_time):
self.id = id
self.day_of_week = day_of_week
self.start_time = start_time
self.end_time = end_time
Planning Entities
To declare Planning Entities, use the @planning_entity decorator
from optapy import planning_entity, planning_id, planning_variable
@planning_entity
class Lesson:
def __init__(self, id, subject, teacher, student_group, timeslot=None, room=None):
self.id = id
self.subject = subject
self.teacher = teacher
self.student_group = student_group
self.timeslot = timeslot
self.room = room
@planning_id
def get_id(self):
return self.id
@planning_variable(Timeslot, value_range_provider_refs=["timeslotRange"])
def get_timeslot(self):
return self.timeslot
def set_timeslot(self, new_timeslot):
self.timeslot = new_timeslot
@planning_variable(Room, value_range_provider_refs=["roomRange"])
def get_room(self):
return self.room
def set_room(self, new_room):
self.room = newRoom
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@planning_variablemethod decorators are used to indicate what fields can change. The method MUST begin with get and have a corresponding set method (i.e.get_room(self),set_room(self, newRoom)). The first parameter of the decorator is the type of the Planning Variable (required). Thevalue_range_provider_refsparameter tells OptaPlanner what value range providers on the Planning Solution this Planning Variable can take values from. -
@planning_idis used to uniquely identify an entity object of a particular class. The same Planning Id can be used on entities of different classes, but the ids of all entities in the same class must be different.
Planning Solution
To declare the Planning Solution, use the @planning_solution decorator
from optapy import planning_solution, problem_fact_collection_property, value_range_provider, planning_entity_collection_property, planning_score
@planning_solution
class TimeTable:
def __init__(self, timeslot_list, room_list, lesson_list, score=None):
self.timeslot_list = timeslot_list
self.room_list = room_list
self.lesson_list = lesson_list
self.score = score
@problem_fact_collection_property(Timeslot)
@value_range_provider(range_id = "timeslotRange")
def get_timeslot_list(self):
return self.timeslot_list
@problem_fact_collection_property(Room)
@value_range_provider(range_id = "roomRange")
def get_room_list(self):
return self.room_list
@planning_entity_collection_property(Lesson)
def get_lesson_list(self):
return self.lesson_list
@planning_score(HardSoftScore)
def get_score(self):
return self.score
def set_score(self, score):
self.score = score
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@value_range_provider(range_id)is used to indicate a method returns values a Planning Variable can take. It can be referenced by its id in thevalue_range_provider_refsparameter of@planning_variable. It should also have a@problem_fact_collection_propertyor a@planning_entity_collection_property. -
@problem_fact_collection_property(type)is used to indicate a method returns Problem Facts. The first parameter of the decorator is the type of the Problem Fact Collection (required). It should be a list. -
@planning_entity_collection_property(type)is used to indicate a method returns Planning Entities. The first parameter of the decorator is the type of the Planning Entity Collection (required). It should be a list. -
@planning_score(scoreType)is used to tell OptaPlanner what field holds the score. The method MUST begin with get and have a corresponding set method (i.e.get_score(self),set_score(self, score)). The first parameter of the decorator is the score type (required).
Constraints
You define your constraints by using the ConstraintFactory
from domain import Lesson
from optapy import get_class, constraint_provider
from optapy.types import Joiners, HardSoftScore
# Get the Java class corresponding to the Lesson Python class
LessonClass = get_class(Lesson)
@constraint_provider
def define_constraints(constraint_factory):
return [
# Hard constraints
room_conflict(constraint_factory),
# Other constraints here...
]
def room_conflict(constraint_factory):
# A room can accommodate at most one lesson at the same time.
return constraint_factory \
.fromUniquePair(LessonClass, [
# ... in the same timeslot ...
Joiners.equal(lambda lesson: lesson.timeslot),
# ... in the same room ...
Joiners.equal(lambda lesson: lesson.room)]) \
.penalize("Room conflict", HardSoftScore.ONE_HARD)
for more details on Constraint Streams, see https://docs.optaplanner.org/latest/optaplanner-docs/html_single/index.html#constraintStreams
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Note
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Since from is a keyword in python, to use the constraint_factory.from(class, [joiners…]) function, you access it like constraint_factory.from_(class, [joiners…]) |
Solve
from optapy import get_class, solve
from optapy.types import SolverConfig, Duration
from constraints import define_constraints
from domain import TimeTable, Lesson, generate_problem
solver_config = SolverConfig().withEntityClasses(get_class(Lesson)) \
.withSolutionClass(get_class(TimeTable)) \
.withConstraintProviderClass(get_class(define_constraints)) \
.withTerminationSpentLimit(Duration.ofSeconds(30))
solution = solve(solver_config, generate_problem())
solution will be a TimeTable instance with planning variables set to the final best solution found.
Build
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Install the python
buildmodule (if not already installed):pip install build
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In the
optapy-coredirectory, use the command below to build the optapy python wheel into thedistdirectory:cd optapy-core python -m build -
Install it into a virtual environment using
pip:# Activate a virtual environment first source my_project/venv/bin/activate pip install dist/optapy-*-py3-none-any.whl
Run
Running run.sh runs optapy-quickstarts/school-timetabling/main.py after building optapy and installing it to optapy-quickstarts/school-timetabling/venv.
More information
For a complete example, see the school timetabling quickstart. For a full API spec, visit OptaPlanner Documentation.
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