Require image info in a fixed format

repo2docker/app.py

@@ -670,10 +670,9 @@ class Repo2Docker(Application):
         # check if we already have an image for this content
         client = self.get_engine()
         for image in client.images():
-            if image["RepoTags"] is not None:
-                for tag in image["RepoTags"]:
-                    if tag == self.output_image_spec + ":latest":
-                        return True
+            for tag in image.tags:
+                if tag == self.output_image_spec + ":latest":
+                    return True
         return False
 
     def build(self):

repo2docker/docker.py

@@ -3,7 +3,7 @@ Docker container engine for repo2docker
 """
 
 import docker
-from .engine import Container, ContainerEngine, ContainerEngineException
+from .engine import Container, ContainerEngine, ContainerEngineException, Image
 
 
 class DockerContainer(Container):
@@ -78,7 +78,8 @@ class DockerEngine(ContainerEngine):
         )
 
     def images(self):
-        return self._apiclient.images()
+        images = self._apiclient.images()
+        return [Image(tags=image["RepoTags"]) for image in images]
 
     def inspect_image(self, image):
         return self._apiclient.inspect_image(image)

repo2docker/engine.py

@@ -84,9 +84,31 @@ class Container(ABC):
         """
 
 
+class Image:
+    """
+    Information about a container image
+    """
+
+    def __init__(self, *, tags):
+        self._tags = tags or []
+
+    @property
+    def tags(self):
+        """
+        A list of tags associated with an image.
+
+        If locally built images have a localhost prefix this prefix should be removed or the image may not be recognised.
+        If there are no tags [] will be returned.
+        """
+        return self._tags
+
+    def __repr__(self):
+        return "Image(tags={})".format(self.tags)
+
+
 class ContainerEngine(ABC):
     """
-    Abstract container engine
+    Abstract container engine.
     """
 
     # containers = Container
@@ -156,7 +178,7 @@ class ContainerEngine(ABC):
 
         Returns
         -------
-        list[str] : List of images
+        list[Image] : List of Image objects.
         """
 
     @abstractmethod