Error when attempting to generate image w/o source

imagekit/exceptions.py

@@ -13,6 +13,10 @@ class MissingGeneratorId(Exception):
     pass
 
 
+class MissingSource(ValueError):
+    pass
+
+
 # Aliases for backwards compatibility
 UnknownExtensionError = UnknownExtension
 UnknownFormatError = UnknownFormat

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)

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()