factory_boy

factory_boy is a fixtures replacement based on thoughtbot's factory_girl.

Its features include:

• Straightforward syntax
• Support for multiple build strategies (saved/unsaved instances, attribute dicts, stubbed objects)
• Powerful helpers for common cases (sequences, sub-factories, reverse dependencies, circular factories, ...)
• Multiple factories per class support, including inheritance
• Support for various ORMs (currently Django, Mogo)

The official repository is at http://github.com/rbarrois/factory_boy; the documentation at http://readthedocs.org/docs/factoryboy/.

factory_boy supports Python 2.6 and 2.7 (Python 3 is in the works), and requires only the standard Python library.

Download

Github: http://github.com/rbarrois/factory_boy/

PyPI:

$ pip install factory_boy

Source:

$ git clone git://github.com/rbarrois/factory_boy/
$ python setup.py install

Defining factories

Factories declare a set of attributes used to instantiate an object. The class of the object must be defined in the FACTORY_FOR attribute:

import factory
from models import User

class UserFactory(factory.Factory):
    FACTORY_FOR = User

    first_name = 'John'
    last_name = 'Doe'
    admin = False

# Another, different, factory for the same object
class AdminFactory(factory.Factory):
    FACTORY_FOR = User

    first_name = 'Admin'
    last_name = 'User'
    admin = True

Using factories

factory_boy supports several different build strategies: build, create, attributes and stub:

# Returns a User instance that's not saved
user = UserFactory.build()

# Returns a saved User instance
user = UserFactory.create()

# Returns a dict of attributes that can be used to build a User instance
attributes = UserFactory.attributes()

You can use the Factory class as a shortcut for the default build strategy:

# Same as UserFactory.create()
user = UserFactory()

No matter which strategy is used, it's possible to override the defined attributes by passing keyword arguments:

# Build a User instance and override first_name
>>> user = UserFactory.build(first_name='Joe')
>>> user.first_name
"Joe"

Lazy Attributes

Most factory attributes can be added using static values that are evaluated when the factory is defined, but some attributes (such as associations and other attributes that must be dynamically generated) will need values assigned each time an instance is generated. These "lazy" attributes can be added as follows:

class UserFactory(factory.Factory):
    first_name = 'Joe'
    last_name = 'Blow'
    email = factory.LazyAttribute(lambda a: '{0}.{1}@example.com'.format(a.first_name, a.last_name).lower())

>>> UserFactory().email
"joe.blow@example.com"

The function passed to LazyAttribute is given the attributes defined for the factory up to the point of the LazyAttribute declaration. If a lambda won't cut it, the lazy_attribute decorator can be used to wrap a function:

# Stub factories don't have an associated class.
class SumFactory(factory.StubFactory):
    lhs = 1
    rhs = 1

    @lazy_attribute
    def sum(a):
        result = a.lhs + a.rhs  # Or some other fancy calculation
        return result

Associations

Associated instances can also be generated using SubFactory:

from models import Post

class PostFactory(factory.Factory):
    author = factory.SubFactory(UserFactory)

The associated object's strategy will be used:

# Builds and saves a User and a Post
post = PostFactory()
post.id == None           # => False
post.author.id == None    # => False

# Builds but does not save a User, and then builds but does not save a Post
post = PostFactory.build()
post.id == None           # => True
post.author.id == None    # => True

Inheritance

You can easily create multiple factories for the same class without repeating common attributes by using inheritance:

class PostFactory(factory.Factory):
    title = 'A title'

class ApprovedPost(PostFactory):
    approved = True
    approver = factory.SubFactory(UserFactory)

Sequences

Unique values in a specific format (for example, e-mail addresses) can be generated using sequences. Sequences are defined by using Sequence or the decorator sequence:

class UserFactory(factory.Factory):
    email = factory.Sequence(lambda n: 'person{0}@example.com'.format(n))

UserFactory().email  # => 'person0@example.com'
UserFactory().email  # => 'person1@example.com'

Sequences can be combined with lazy attributes:

class UserFactory(factory.Factory):
    name = 'Mark'
    email = factory.LazyAttributeSequence(lambda a, n: '{0}+{1}@example.com'.format(a.name, n).lower())

UserFactory().email  # => mark+0@example.com

If you wish to use a custom method to set the initial ID for a sequence, you can override the _setup_next_sequence class method:

class MyFactory(factory.Factory):

    @classmethod
    def _setup_next_sequence(cls):
        return cls.FACTORY_FOR.objects.values_list('id').order_by('-id')[0] + 1

Customizing creation

Sometimes, the default build/create by keyword arguments doesn't allow for enough customization of the generated objects. In such cases, you should override the Factory._prepare method:

class UserFactory(factory.Factory):
    @classmethod
    def _prepare(cls, create, **kwargs):
        password = kwargs.pop('password', None)
        user = super(UserFactory, cls)._prepare(create, **kwargs)
        if password:
            user.set_password(password)
            if create:
                user.save()
        return user

Subfactories

If one of your factories has a field which is another factory, you can declare it as a SubFactory. This allows to define attributes of that field when calling the global factory, using a simple syntax : field__attr=42 will set the attribute attr of the SubFactory defined in field to 42:

class InnerFactory(factory.Factory):
    foo = 'foo'
    bar = factory.LazyAttribute(lambda o: foo * 2)

class ExternalFactory(factory.Factory):
    inner = factory.SubFactory(InnerFactory, foo='bar')

>>> e = ExternalFactory()
>>> e.foo
'bar'
>>> e.bar
'barbar'

>>> e2 : ExternalFactory(inner__bar='baz')
>>> e2.foo
'bar'
>>> e2.bar
'baz'

Abstract factories

If a Factory simply defines generic attribute declarations without being bound to a given class, it should be marked 'abstract' by declaring FACTORY_ABSTRACT = True. Such factories cannot be built/created/....

class AbstractFactory(factory.Factory):
    FACTORY_ABSTRACT = True
    foo = 'foo'

>>> AbstractFactory()
Traceback (most recent call last):
  ...
AttributeError: type object 'AbstractFactory' has no attribute '_associated_class'

Contributing

factory_boy is distributed under the MIT License.

Issues should be opened through GitHub Issues; whenever possible, a pull request should be included.

All pull request should pass the test suite, which can be launched simply with:

$ python setup.py test

In order to test coverage, please use:

$ pip install coverage
$ coverage erase; coverage run --branch setup.py test; coverage report

Contents, indices and tables

.. toctree::
    :maxdepth: 2

    examples
    subfactory
    post_generation
    changelog

• :ref:`genindex`
• :ref:`modindex`
• :ref:`search`