owlready2

library0.50pypypi✓ verified 83d ago

Owlready2 is a Python library for ontology-oriented programming, allowing users to load OWL 2.0 ontologies as Python objects, modify them, save them, and perform reasoning via the HermiT reasoner. It includes an optimized RDF quadstore. Current version is 0.50 (as of latest release) and it follows an irregular release cadence. Requires Python >=3.6.

data

pip install owlready2

package ↗homepage ↗

INSTALL

IMPORT

SIG · OWLREADY2

owlready2

datapythonv0.50

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

default_world

✓ from owlready2 import default_world

✗ import owlready2

Importing the module does not automatically expose default_world; use explicit import.

World

✓ from owlready2 import World

get_ontology

✓ from owlready2 import get_ontology

sync_reasoner

✓ from owlready2 import sync_reasoner

Thing

✓ from owlready2 import Thing

Property

✓ from owlready2 import Property

Load an OWL ontology, create classes, individuals, and properties, then run the HermiT reasoner.

from owlready2 import get_ontology, sync_reasoner, Thing, Property, default_world # Load an ontology from a URL or local file onto = get_ontology("http://www.semanticweb.org/owl/owlapi/tutorial/people.owl").load() # Create new classes and properties with onto: class Person(Thing): pass class WorksFor(Property): domain = [Person] range = [Person] # Create individuals john = Person("John") mary = Person("Mary") john.WorksFor = [mary] # Save ontology onto.save() # Run reasoning sync_reasoner() # Print all individuals for person in onto.Person.instances(): print(person.name)

Debug

Known issues

gotchaThe default_world is global; modifying it can affect other parts of the program. Use separate World() instances for isolation.

fix

Use `world = World()` and `onto = world.get_ontology(...)` instead of relying on the default world.

affects: all

breakingOwlready2 changed the import path from the deprecated Owlready (no '2') in older versions. Code using `import owlready` will break.

fix

Use `import owlready2` and `from owlready2 import ...`

affects: <0.30

gotchaModifying ontology entities (e.g., adding properties) must be done inside a `with onto:` block. Otherwise, changes may not persist or cause errors.

fix

Always use `with onto: ...` when defining classes or properties.

affects: all

deprecatedThe `sync_reasoner()` function is deprecated in favor of using the HermiT reasoner directly with `sync_reasoner_hermit()`. However, `sync_reasoner()` still works for now.

fix

Use `sync_reasoner_hermit()` instead.

affects: >=0.50

gotchaInstalling Owlready2 may fail on some systems due to missing C++ build tools required for the quadstore (cysignals). Ensure you have a C++ compiler installed.

fix

Install build tools: on Windows install Microsoft C++ Build Tools; on Linux install g++ and python3-dev.

affects: all

Errors

Common errors & fixes

ModuleNotFoundError: No module named 'owlready2'

Owlready2 is not installed, or the wrong import path is used.

fix

Run `pip install owlready2` and use `import owlready2`.

AttributeError: module 'owlready2' has no attribute 'default_world'

Import was not explicit; `default_world` is not automatically imported with `import owlready2`.

fix

Use `from owlready2 import default_world`.

NameError: name 'Thing' is not defined

Thing is not imported.

fix

Add `from owlready2 import Thing` to your imports.

Owlready2_OwlException: Cannot define class outside of a `with ontology:` block

Trying to define classes or properties without the `with onto:` context manager.

fix

Wrap class definitions inside `with onto:`.

AttributeError: 'Ontology' object has no attribute 'save' (or similar)

Possibly using an outdated version where save syntax is different.

fix

Update to latest version and use `onto.save()`.

Upgrade

Version history

0.50latest on PyPI · released Feb 5, 2026

Audit

Dependencies

No dependency data recorded yet.

Agent activity

10 hits · last 30 days

node

Amazon

Resources

packagehttps://pypi.org/project/owlready2/ ↗

homepagehttps://pypi.org/project/Owlready2/ ↗