From 92a3c2688cfa2a63687228765342422cd3ee362a Mon Sep 17 00:00:00 2001
From: Matthew Tretter <m@tthewwithanm.com>
Date: Mon, 25 Feb 2013 22:34:24 -0500
Subject: [PATCH] Error when attempting to generate image w/o source

---
 imagekit/exceptions.py     |  4 ++++
 imagekit/specs/__init__.py | 12 ++++++++++++
 tests/test_specs.py        |  9 ++++++++-
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/imagekit/exceptions.py b/imagekit/exceptions.py
index 0c46514..9aba018 100644
--- a/imagekit/exceptions.py
+++ b/imagekit/exceptions.py
@@ -13,6 +13,10 @@ class MissingGeneratorId(Exception):
     pass
 
 
+class MissingSource(ValueError):
+    pass
+
+
 # Aliases for backwards compatibility
 UnknownExtensionError = UnknownExtension
 UnknownFormatError = UnknownFormat
diff --git a/imagekit/specs/__init__.py b/imagekit/specs/__init__.py
index a8fa742..c12acfa 100644
--- a/imagekit/specs/__init__.py
+++ b/imagekit/specs/__init__.py
@@ -4,6 +4,7 @@ from hashlib import md5
 import pickle
 from ..cachefiles.backends import get_default_cachefile_backend
 from ..cachefiles.strategies import StrategyWrapper
+from ..exceptions import MissingSource
 from ..processors import ProcessorPipeline
 from ..utils import open_image, img_to_fobj, get_by_qname
 from ..registry import generator_registry, register
@@ -41,6 +42,13 @@ class BaseImageSpec(object):
     def generate(self):
         raise NotImplementedError
 
+    MissingSource = MissingSource
+    """
+    Raised when an operation requiring a source is attempted on a spec that has
+    no source.
+
+    """
+
 
 class ImageSpec(BaseImageSpec):
     """
@@ -116,6 +124,10 @@ class ImageSpec(BaseImageSpec):
         ])).hexdigest()
 
     def generate(self):
+        if not self.source:
+            raise MissingSource("The spec '%s' has no source file associated"
+                                " with it." % self)
+
         # TODO: Move into a generator base class
         # TODO: Factor out a generate_image function so you can create a generator and only override the PIL.Image creating part. (The tricky part is how to deal with original_format since generator base class won't have one.)
         img = open_image(self.source)
diff --git a/tests/test_specs.py b/tests/test_specs.py
index 6c8c4b9..5db081f 100644
--- a/tests/test_specs.py
+++ b/tests/test_specs.py
@@ -1,5 +1,5 @@
 from imagekit.cachefiles import ImageCacheFile
-from nose.tools import assert_false
+from nose.tools import assert_false, raises
 from .imagegenerators import TestSpec
 
 
@@ -10,3 +10,10 @@ def test_no_source():
     spec = TestSpec(source=None)
     file = ImageCacheFile(spec)
     assert_false(bool(file))
+
+
+@raises(TestSpec.MissingSource)
+def test_no_source_error():
+    spec = TestSpec(source=None)
+    file = ImageCacheFile(spec)
+    file.generate()