A test fixtures replacement for Python
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factory_boy is a fixtures replacement based on thoughtbot's factory_girl . Like factory_girl it has a straightforward definition syntax, support for multiple build strategies (saved instances, unsaved instances, attribute dicts, and stubbed objects), and support for multiple factories for the same class, including factory inheritance. Django support is included, and support for other ORMs can be easily added.

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


This README parallels the factory_girl README as much as possible; text and examples are reproduced for comparison purposes. Ruby users of factory_girl should feel right at home with factory_boy in Python.

factory_boy was originally written by Mark Sandstrom, and improved by Raphaël Barrois.

Thank you Joe Ferris and thoughtbot for creating factory_girl.


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


pip install factory_boy


# Download the source and run
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()

# Returns an object with all defined attributes stubbed out:
stub = UserFactory.stub()

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

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

The default strategy can be overridden:

UserFactory.default_strategy = factory.BUILD_STRATEGY
user = UserFactory()

The default strategy can also be overridden for all factories:

# This will set the default strategy for all factories that don't define a default build strategy
factory.Factory.default_strategy = factory.BUILD_STRATEGY

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')
# => '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())

# => '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

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


Associated instances can also be generated using LazyAttribute:

from models import Post

class PostFactory(factory.Factory):
    author = factory.LazyAttribute(lambda a: UserFactory())

The associated object's default strategy is always used:

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

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


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.LazyAttribute(lambda a: UserFactory())


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):

    def _setup_next_sequence(cls):
        return cls._associated_class.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):
    def _prepare(cls, create, **kwargs):
        password = kwargs.pop('password', None)
        user = super(UserFactory, cls)._prepare(create, **kwargs)
        if password:
            if create:
        return user


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
>>> e.bar

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

Abstract factories

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

class AbstractFactory(factory.Factory):
ABSTRACT_FACTORY = True foo = 'foo'
>>> AbstractFactory()
Traceback (most recent call last):
AttributeError: type object 'AbstractFactory' has no attribute '_associated_class'