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``.

1 files changed, 10 insertions, 2 deletions

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)