diff --git a/build-tag-push.py b/build-tag-push.py
index 6fafee42..a47591d9 100755
--- a/build-tag-push.py
+++ b/build-tag-push.py
@@ -12,24 +12,37 @@ if not user_name:
     print("export DOCKERHUB_USER=zoe")
     exit(1)
 
+# Execute "docker-compose build" and abort if it fails.
 subprocess.check_call(["docker-compose", "build"])
 
+# Get the name of the current directory.
 project_name = os.path.basename(os.path.realpath("."))
 
+# Generate a Docker image tag, using the UNIX timestamp.
+# (i.e. number of seconds since January 1st, 1970)
 version = str(int(time.time()))
 
+# Load the services from docker-compose.yml.
 stack = yaml.load(open("docker-compose.yml"))
+
+# Iterate over all services that have a "build" definition.
 for service_name, service in stack.items():
     if "build" in service:
         compose_image = "{}_{}".format(project_name, service_name)
         hub_image = "{}/{}_{}:{}".format(user_name, project_name, service_name, version)
+        # Re-tag the image so that it can be uploaded to the Docker Hub.
         subprocess.check_call(["docker", "tag", compose_image, hub_image])
+        # Execute "docker push" to upload the image.
         subprocess.check_call(["docker", "push", hub_image])
+        # Replace the "build" definition by an "image" definition,
+        # using the name of the image on the Docker Hub.
         del service["build"]
         service["image"] = hub_image
 
+# Write the new docker-compose.yml file.
 new_compose_file = "docker-compose.yml-{}".format(version)
 with open(new_compose_file, "w") as f:
     yaml.safe_dump(stack, f)
+
 print("You can now use:")
 print("docker-compose -f {}".format(new_compose_file))