Removes an error message when destroying docker

If the 'upload' and 'download' commands have never been used, the
current image and the initial image are one and the same. Deleting the
second time would previously log an error, although everything went
smooth.

CHANGELOG.md

@@ -7,6 +7,7 @@ Changelog
 Bugfixes:
 * Fixes `debug` log messages not being printed
 * Pressing Ctrl+C wouldn't stop package identification with KeyboardInterrupt
+* Fixes an error message while destroying a docker experiment
 
 0.5.1 (2014-12-18)
 ------------------

reprounzip-docker/reprounzip/unpackers/docker.py

@@ -417,18 +417,20 @@ def docker_destroy_docker(args):
             logging.error("Error deleting container %s",
                           container.decode('ascii'))
 
+    initial_image = unpacked_info.pop('initial_image')
+
     if 'current_image' in unpacked_info:
         image = unpacked_info.pop('current_image')
-        logging.info("Destroying image %s...", image.decode('ascii'))
-        retcode = subprocess.call(['docker', 'rmi', image])
-        if retcode != 0:
-            logging.error("Error deleting image %s", image.decode('ascii'))
-
-    image = unpacked_info.pop('initial_image')
-    logging.info("Destroying image %s...", image.decode('ascii'))
-    retcode = subprocess.call(['docker', 'rmi', image])
+        if image != initial_image:
+            logging.info("Destroying image %s...", image.decode('ascii'))
+            retcode = subprocess.call(['docker', 'rmi', image])
+            if retcode != 0:
+                logging.error("Error deleting image %s", image.decode('ascii'))
+
+    logging.info("Destroying image %s...", initial_image.decode('ascii'))
+    retcode = subprocess.call(['docker', 'rmi', initial_image])
     if retcode != 0:
-        logging.error("Error deleting image %s", image.decode('ascii'))
+        logging.error("Error deleting image %s", initial_image.decode('ascii'))
 
 
 @target_must_exist