Is there a way to tell Python to halt execution at a certain point in a script and wait for a debugger to attach to the process?
Is there something similar to dot-Net's Debugger.Break() in Python?
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5 Answers
Different IDEs can use different methods for attaching to the process, however PyCharm, Eclipse, Visual Studio, and VS Code all use pydevd (VS/VSC via their Python plugin via ptvsd) to provide their in-process debugger implementation. As a result, we can target those with one piece of code.
The idea is to wait until pydevd is imported and then stop at a breakpoint.
import sys import threading from importlib.abc import MetaPathFinder class NotificationFinder(MetaPathFinder): def find_spec(self, fullname, _path, _target=None): if 'pydevd' in fullname: with t: t.notify() t = threading.Condition() sys.meta_path.insert(0, NotificationFinder()) with t: t.wait() breakpoint() Since pydevd creates __builtins__.breakpoint, this should work regardless of the Python version. I tested in PyCharm (Community Edition 2019.1.3). I started the script, attached with the "Attach to process" option in my IDE, and was able to attach successfully. The script then stopped at breakpoint() as expected.
1 Comment
Felix D.
This allows to attach to programs with a more complicated launch strategy, like ROS & ROS2!
Install ipython and ipdb. Afterwards you can just use
import ipdb ipdb.set_trace() And debug straight from the console. You can also use pdb which comes straight out of the box:
import pdb pdb.set_trace() 3 Comments
Daniel Roseman
ipdb is great, but pdb comes built-in with Python.
Nitzan
Still, I'm very interested in debugging from tools like PyCharm, and from my understanding pdb is limited to the console. Is there a way I could break and attach using a tool like PyCharm?
GLaDOS
Well that would work differently. You can look up tutorials for it like this one: jetbrains.com/pycharm/help/remote-debugging.html
Here is another way you can wait for pydevd:
while not (pydevd.connected and get_global_debugger().ready_to_run): sleep(0.3) breakpoint() In my setup MetaPathFinder was firing only the first time I would connect with pydevd. With a while loop you should be able to reconnect because you are not relying on pydevd import side effect.
Comments
Improving on Timofey Solonin's answer https://stackoverflow.com/a/66841531/324204.
# ... import pydevd import time while pydevd.get_global_debugger() is None or not pydevd.get_global_debugger().ready_to_run: time.sleep(0.3) breakpoint() # breaks here # ... The improvement is to not use pydevd.connected. It is not defined in pydevd version 2.8.
Note that on Linux you may have a problem with having no permissions to attach to the process. How to solve "ptrace operation not permitted" when trying to attach GDB to a process?
Comments
You can use my tool madbg to do exactly that. Put this in your program:
madbg.set_trace() This line will block until a debugger connects using:
madbg connect madbg could connect from the same machine or over the network. It could also preemptively stop your process and attach to it.
