pdb
is a powerful debugging tool that is included as a Python standard library. It can seriously speed up, our debug process, while resolving certain bugs
for this
Problematic
Trying to initiate the pdb
in your docker-compose
container will result in the following error.
...
...
return self.view_functions[rule.endpoint](**req.view_args)
File "/backend/app.py", line 25, in test_response
return response
File "/backend/app.py", line 25, in test_response
return response
File "/usr/local/lib/python3.9/bdb.py", line 88, in trace_dispatch
return self.dispatch_line(frame)
File "/usr/local/lib/python3.9/bdb.py", line 113, in dispatch_line
if self.quitting: raise BdbQuit
bdb.BdbQuit
that happens only if you try to run pdb
in docker-compose
and not via docker run ...
, due to up
not being an interactive command by design.
more on this topic: https://github.com/docker/compose/issues/4677
you can try in out yourself:
step 1. clone the repo setup repo with the minimal Flask
app in docker-compose
.
https://github.com/zahaar/docker-pdb-interactive-debugging/
step 2. cd docker-pdb-interactive-debugging
step 3. checkout on docker-error
branch
git checkout docker-error
step 4. run docker compose up
, or docker-compose up
if you are using old docker CLI version
step 5. in a separate shell run curl
command.
curl -XGET 'http://localhost:5000/api/v1.0/the_answer'
you would see the expected pdb.DdbQuit
exception error:
...
...
File "/usr/local/lib/python3.9/bdb.py", line 113, in dispatch_line
if self.quitting: raise BdbQuit
bdb.BdbQuit
Solution
pdb
expects an open TTY, so let's add it to our compose
file
...
...
ports:
- '5000:5000'
stdin_open: true # für pdb
tty: true # für pdb
Let's try recreating the steps:
Step 1. git clone https://github.com/zahaar/docker-pdb-interactive-debugging/
, but on a main
branch this time
Step 2. docker compose up
Step 3. In a separate shell window attach local input to a running container, by running.
docker attach docker-interractive-debugging_api_1 // container name
Note we have this capability only after opening an TTY for our container
Step 4. In a separate shell window run.
curl -XGET 'http://localhost:5000/api/v1.0/the_answer'
Step 5. now in the window where container output was attached
you would see, pdb
waiting for commands.
you can:
-
p true_response
to print the value of the variabletrue_response
-
c
to resume normal flow - to all other crazy things with
pdb
!!!
That's it. Easy.
Important Note: to stop attached window without stopping the main running container, you have to use,
escape sequence:CTRL + p -> CTRL + q
Tip:
checkout pdb
commands cheatsheet
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