Split 'build' function out of start

repo2docker/__main__.py

@@ -237,15 +237,18 @@ def make_r2d(argv=None):
     if args.image_name:
         r2d.output_image_spec = args.image_name
 
-    r2d.push = args.push
-    r2d.run = args.run
     r2d.json_logs = args.json_logs
 
     r2d.build = args.build
-    if not r2d.build:
+
+    if not args.build:
         # Can't push nor run if we aren't building
-        r2d.run = False
-        r2d.push = False
+        args.run = False
+        args.push = False
+
+    r2d.build = args.build
+    r2d.run = args.run
+    r2d.push = args.push
 
     # check against r2d.run and not args.run as r2d.run is false on
     # --no-build

repo2docker/app.py

@@ -551,6 +551,10 @@ class Repo2Docker(Application):
                     raise e
                 sys.exit(1)
 
+    def build(self):
+        """
+        Build docker image
+        """
         # If the source to be executed is a directory, continue using the
         # directory. In the case of a local directory, it is used as both the
         # source and target. Reusing a local directory seems better than
@@ -620,6 +624,9 @@ class Repo2Docker(Application):
             if self.cleanup_checkout:
                 shutil.rmtree(checkout_path, ignore_errors=True)
 
+    def start(self):
+        self.build()
+
         if self.push:
             self.push_image()