Allow lazy evaluation of FuzzyChoice's iterators (Closes #184).

This allows the following idiom:
``user = factory.fuzzy.FuzzyChoice(User.objects.all())``

Previously, the ``User.objects.all()`` queryset would have been
evaluated *at import time*; it is now evaluated with the first use of the
``FuzzyChoice``.

4 files changed, 34 insertions, 4 deletions

diff --git a/docs/changelog.rst b/docs/changelog.rst
index ebe9930..13fdd68 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -10,6 +10,7 @@ ChangeLog
 *New:*
 
     - Add support for getting/setting :mod:`factory.fuzzy`'s random state (see :issue:`175`, :issue:`185`).
+    - Support lazy evaluation of iterables in :class:`factory.fuzzy.FuzzyChoice` (see :issue:`184`).
 
 *Deprecation:*
 
diff --git a/docs/fuzzy.rst b/docs/fuzzy.rst
index 0658652..18978e4 100644
--- a/docs/fuzzy.rst
+++ b/docs/fuzzy.rst
@@ -62,8 +62,11 @@ FuzzyChoice
     The :class:`FuzzyChoice` fuzzer yields random choices from the given
     iterable.
 
-    .. note:: The passed in :attr:`choices` will be converted into a list at
-              declaration time.
+    .. note:: The passed in :attr:`choices` will be converted into a list upon
+              first use, not at declaration time.
+
+              This allows passing in, for instance, a Django queryset that will
+              only hit the database during the database, not at import time.
 
     .. attribute:: choices
 
diff --git a/factory/fuzzy.py b/factory/fuzzy.py
index 564264e..4e6a03d 100644
--- a/factory/fuzzy.py
+++ b/factory/fuzzy.py
@@ -113,13 +113,21 @@ class FuzzyText(BaseFuzzyAttribute):
 
 
 class FuzzyChoice(BaseFuzzyAttribute):
-    """Handles fuzzy choice of an attribute."""
+    """Handles fuzzy choice of an attribute.
+    
+    Args:
+        choices (iterable): An iterable yielding options; will only be unrolled
+            on the first call.
+    """
 
     def __init__(self, choices, **kwargs):
-        self.choices = list(choices)
+        self.choices = None
+        self.choices_generator = choices
         super(FuzzyChoice, self).__init__(**kwargs)
 
     def fuzz(self):
+        if self.choices is None:
+            self.choices = list(self.choices_generator)
         return _random.choice(self.choices)
 
 
diff --git a/tests/test_fuzzy.py b/tests/test_fuzzy.py
index fd32705..c7e1106 100644
--- a/tests/test_fuzzy.py
+++ b/tests/test_fuzzy.py
@@ -74,6 +74,24 @@ class FuzzyChoiceTestCase(unittest.TestCase):
         res = d.evaluate(2, None, False)
         self.assertIn(res, [0, 1, 2])
 
+    def test_lazy_generator(self):
+        class Gen(object):
+            def __init__(self, options):
+                self.options = options
+                self.unrolled = False
+
+            def __iter__(self):
+                self.unrolled = True
+                return iter(self.options)
+
+        opts = Gen([1, 2, 3])
+        d = fuzzy.FuzzyChoice(opts)
+        self.assertFalse(opts.unrolled)
+
+        res = d.evaluate(2, None, False)
+        self.assertIn(res, [1, 2, 3])
+        self.assertTrue(opts.unrolled)
+
 
 class FuzzyIntegerTestCase(unittest.TestCase):
     def test_definition(self):