Flush output in Python before running execvp (#2258)

images/base-notebook/start-notebook.py

@@ -8,7 +8,8 @@ import sys
 # If we are in a JupyterHub, we pass on to `start-singleuser.py` instead so it does the right thing
 if "JUPYTERHUB_API_TOKEN" in os.environ:
     print(
-        "WARNING: using start-singleuser.py instead of start-notebook.py to start a server associated with JupyterHub."
+        "WARNING: using start-singleuser.py instead of start-notebook.py to start a server associated with JupyterHub.",
+        flush=True,
     )
     command = ["/usr/local/bin/start-singleuser.py"] + sys.argv[1:]
     os.execvp(command[0], command)
@@ -40,5 +41,5 @@ if "NOTEBOOK_ARGS" in os.environ:
 command += sys.argv[1:]
 
 # Execute the command!
-print("Executing: " + " ".join(command))
+print("Executing: " + " ".join(command), flush=True)
 os.execvp(command[0], command)

images/base-notebook/start-singleuser.py

@@ -20,5 +20,5 @@ if "NOTEBOOK_ARGS" in os.environ:
 command += sys.argv[1:]
 
 # Execute the command!
-print("Executing: " + " ".join(command))
+print("Executing: " + " ".join(command), flush=True)
 os.execvp(command[0], command)

tests/by_image/base-notebook/test_start_container.py

@@ -42,11 +42,7 @@ def test_start_notebook(
         f"Test that the start-notebook.py launches the {expected_command} server from the env {env} ..."
     )
     host_port = find_free_port()
-    container.run_detached(
-        tty=True,
-        environment=env,
-        ports={"8888/tcp": host_port},
-    )
+    container.run_detached(environment=env, ports={"8888/tcp": host_port})
     # sleeping some time to let the server start
     time.sleep(2)
     logs = container.get_logs()