factory: LazyFunction to just call a function in the simplest case

README.rst

@@ -226,13 +226,18 @@ These "lazy" attributes can be added as follows:
         first_name = 'Joe'
         last_name = 'Blow'
         email = factory.LazyAttribute(lambda a: '{0}.{1}@example.com'.format(a.first_name, a.last_name).lower())
+        date_joined = factory.LazyFunction(datetime.now)
 
 .. code-block:: pycon
 
     >>> UserFactory().email
     "joe.blow@example.com"
 
 
+.. note:: ``LazyAttribute`` calls the function with the object being constructed as an argument, when
+          ``LazyFunction`` does not send any argument.
+
+
 Sequences
 """""""""
 

docs/examples.rst

@@ -49,6 +49,7 @@ And now, we'll define the related factories:
 
 .. code-block:: python
 
+    import datetime
     import factory
     import random
 
@@ -61,6 +62,7 @@ And now, we'll define the related factories:
 
         username = factory.Sequence(lambda n: 'john%s' % n)
         email = factory.LazyAttribute(lambda o: '%s@example.org' % o.username)
+        date_joined = factory.LazyFunction(datetime.datetime.now)
 
 
     class ProfileFactory(factory.Factory):

docs/introduction.rst

@@ -117,6 +117,35 @@ This is achieved with the :class:`~factory.Sequence` declaration:
                     return 'user%d' % n
 
 
+LazyFunction
+------------
+
+In simple cases, calling a function is enough to compute the value. If that function doesn't depend on the object
+being built, use :class:`~factory.LazyFunction` to call that function; it should receive a function taking no
+argument and returning the value for the field:
+
+.. code-block:: python
+
+    class LogFactory(factory.Factory):
+        class Meta:
+            model = models.Log
+
+        timestamp = factory.LazyFunction(datetime.now)
+
+.. code-block:: pycon
+
+    >>> LogFactory()
+    <Log: log at 2016-02-12 17:02:34>
+
+    >>> # The LazyFunction can be overriden
+    >>> LogFactory(timestamp=now - timedelta(days=1))
+    <Log: log at 2016-02-11 17:02:34>
+
+
+.. note:: For complex cases when you happen to write a specific function,
+          the :meth:`~factory.@lazy_attribute` decorator should be more appropriate.
+
+
 LazyAttribute
 -------------
 

docs/reference.rst

@@ -90,7 +90,7 @@ The :class:`Factory` class
                     model = Order
                     exclude = ('now',)
 
-                now = factory.LazyAttribute(lambda o: datetime.datetime.utcnow())
+                now = factory.LazyFunction(datetime.datetime.utcnow)
                 started_at = factory.LazyAttribute(lambda o: o.now - datetime.timedelta(hours=1))
                 paid_at = factory.LazyAttribute(lambda o: o.now - datetime.timedelta(minutes=50))
 
@@ -551,6 +551,42 @@ Faker
                 smiley = factory.Faker('smiley')
 
 
+LazyFunction
+""""""""""""
+
+.. class:: LazyFunction(method_to_call)
+
+The :class:`LazyFunction` is the simplest case where the value of an attribute
+does not depend on the object being built.
+
+It takes as argument a method to call (function, lambda...); that method should
+not take any argument, though keyword arguments are safe but unused,
+and return a value.
+
+.. code-block:: python
+
+    class LogFactory(factory.Factory):
+        class Meta:
+            model = models.Log
+
+        timestamp = factory.LazyFunction(datetime.now)
+
+.. code-block:: pycon
+
+    >>> LogFactory()
+    <Log: log at 2016-02-12 17:02:34>
+
+    >>> # The LazyFunction can be overriden
+    >>> LogFactory(timestamp=now - timedelta(days=1))
+    <Log: log at 2016-02-11 17:02:34>
+
+Decorator
+~~~~~~~~~
+
+The class :class:`LazyFunction` does not provide a decorator.
+
+For complex cases, use :meth:`LazyAttribute.lazy_attribute` directly.
+
 LazyAttribute
 """""""""""""
 
@@ -1041,7 +1077,7 @@ gains an "upward" semantic through the double-dot notation, as used in Python im
     >>> company.owner.language
     'fr'
 
-Obviously, this "follow parents" hability also handles overriding some attributes on call:
+Obviously, this "follow parents" ability also handles overriding some attributes on call:
 
 .. code-block:: pycon
 

factory/__init__.py

@@ -43,6 +43,7 @@
 from .faker import Faker
 
 from .declarations import (
+    LazyFunction,
     LazyAttribute,
     Iterator,
     Sequence,

factory/declarations.py

@@ -57,6 +57,23 @@ def evaluate(self, sequence, obj, create, extra=None, containers=()):
         raise NotImplementedError('This is an abstract method')
 
 
+class LazyFunction(OrderedDeclaration):
+    """Simplest OrderedDeclaration computed by calling the given function.
+
+    Attributes:
+        function (function): a function without arguments and
+            returning the computed value.
+    """
+
+    def __init__(self, function, *args, **kwargs):
+        super(LazyFunction, self).__init__(*args, **kwargs)
+        self.function = function
+
+    def evaluate(self, sequence, obj, create, extra=None, containers=()):
+        logger.debug("LazyFunction: Evaluating %r on %r", self.function, obj)
+        return self.function()
+
+
 class LazyAttribute(OrderedDeclaration):
     """Specific OrderedDeclaration computed using a lambda.
 

tests/test_base.py

@@ -134,25 +134,28 @@ class AbstractFactory(base.Factory):
         self.assertEqual(AbstractFactory, AbstractFactory._meta.counter_reference)
 
     def test_declaration_collecting(self):
-        lazy = declarations.LazyAttribute(lambda _o: 1)
+        lazy = declarations.LazyFunction(int)
+        lazy2 = declarations.LazyAttribute(lambda _o: 1)
         postgen = declarations.PostGenerationDeclaration()
 
         class AbstractFactory(base.Factory):
             x = 1
             y = lazy
+            y2 = lazy2
             z = postgen
 
         # Declarations aren't removed
         self.assertEqual(1, AbstractFactory.x)
         self.assertEqual(lazy, AbstractFactory.y)
+        self.assertEqual(lazy2, AbstractFactory.y2)
         self.assertEqual(postgen, AbstractFactory.z)
 
         # And are available in class Meta
-        self.assertEqual({'x': 1, 'y': lazy}, AbstractFactory._meta.declarations)
+        self.assertEqual({'x': 1, 'y': lazy, 'y2': lazy2}, AbstractFactory._meta.declarations)
         self.assertEqual({'z': postgen}, AbstractFactory._meta.postgen_declarations)
 
     def test_inherited_declaration_collecting(self):
-        lazy = declarations.LazyAttribute(lambda _o: 1)
+        lazy = declarations.LazyFunction(int)
         lazy2 = declarations.LazyAttribute(lambda _o: 2)
         postgen = declarations.PostGenerationDeclaration()
         postgen2 = declarations.PostGenerationDeclaration()
@@ -178,7 +181,7 @@ class OtherFactory(AbstractFactory):
         self.assertEqual({'z': postgen, 'b': postgen2}, OtherFactory._meta.postgen_declarations)
 
     def test_inherited_declaration_shadowing(self):
-        lazy = declarations.LazyAttribute(lambda _o: 1)
+        lazy = declarations.LazyFunction(int)
         lazy2 = declarations.LazyAttribute(lambda _o: 2)
         postgen = declarations.PostGenerationDeclaration()
         postgen2 = declarations.PostGenerationDeclaration()

tests/test_containers.py

@@ -215,6 +215,29 @@ def _generate_next_sequence(cls):
         ab = containers.AttributeBuilder(FakeFactory, extra={'one': seq2})
         self.assertEqual({'one': 'yy1'}, ab.build(create=False))
 
+    def test_lazy_function(self):
+        lf = declarations.LazyFunction(int)
+
+        class FakeFactory(object):
+            @classmethod
+            def declarations(cls, extra):
+                d = {'one': 1, 'two': lf}
+                d.update(extra)
+                return d
+
+            @classmethod
+            def _generate_next_sequence(cls):
+                return 1
+
+        ab = containers.AttributeBuilder(FakeFactory)
+        self.assertEqual({'one': 1, 'two': 0}, ab.build(create=False))
+
+        ab = containers.AttributeBuilder(FakeFactory, {'one': 4})
+        self.assertEqual({'one': 4, 'two': 0}, ab.build(create=False))
+
+        ab = containers.AttributeBuilder(FakeFactory, {'one': 4, 'three': lf})
+        self.assertEqual({'one': 4, 'two': 0, 'three': 0}, ab.build(create=False))
+
     def test_lazy_attribute(self):
         la = declarations.LazyAttribute(lambda a: a.one * 2)