Tracing Python
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Tracing Python
1–10 of 14 posts
Re: Tracing Python
#2A more traditional debugger for Python.
Re: Tracing Python
#3Fantastic article and something I've been looking for better tools for. None of them seem to have my ideal workflow though -- providing an external manifest of what and how to trace that can be used against an existing program without changing the code. Something like Otel's auto instrumentation.
Re: Tracing Python
#4Python has a built-in API for tracing: https://docs.python.org/3/library/sys.html#sys.settrace
Here's an example of how to use it (obviously a minimal case, you can customise your handler do do whatever you need):
def mytrace(frame, event, arg):
if event == "call":
print("call", frame.f_code.co_name, frame.f_locals)
elif event == "return":
print("return", frame.f_code.co_name, arg)
return mytrace
import sys
sys.settrace(mytrace)
def three(z):
return 3
def two(y):
return three("BBB") - 1
def one():
return two("AAA") - 1
one()
call one {}
call two {'y': 'AAA'}
call three {'z': 'BBB'}
return three 3
return two 2
return one 1Re: Tracing Python
#5There are many different tools, but when I want to quickly understand what the code was doing I have been reaching for pysnooper:
https://pypi.org/project/PySnooper/
Has a pretty nice and importantly colored output by default, which I find much easier to follow. In many cases snooping one specific function has done the job. It has an easy to use decorator to decorate any function without having to otherwise intercept the main python invocation or set something up at the start. Good for libraries etc.
pysnooper has mostly been enough for me but the "snoop" mentioned in the article seems to be a superset and more. Will have to give it a go next time.
Outside of this if I want to understand performance or more roughly what code paths are executing (and not a per-statement trace) then austin and py-spy are both amazing.. convert to flamescope and drop into flamescope.app.
Re: Tracing Python
#6What's the modern practical use case for tracing in python? Environments without an IDE/remote debugger?
I can't recall the last time I needed to enable tracing, in the last couple of decades, besides bash scripts.
Re: Tracing Python
#7Python has a built-in API for tracing: https://docs.python.org/3/library/sys.html#sys.settrace Here's an example of how to use it (obviously a minimal case, you can customise your handler do do whatever you need): def mytrace(frame, event, arg): if event == "call": print("call", frame.f_code.co_name, frame.f_locals) elif event == "return": print("return", frame.f_code.co_name, arg) return mytrace import sys sys.settr…
I confess I'm surprised the builtin wasn't one of the demoed options. Curious what the reason is.
Re: Tracing Python
#8Python has a built-in API for tracing: https://docs.python.org/3/library/sys.html#sys.settrace Here's an example of how to use it (obviously a minimal case, you can customise your handler do do whatever you need): def mytrace(frame, event, arg): if event == "call": print("call", frame.f_code.co_name, frame.f_locals) elif event == "return": print("return", frame.f_code.co_name, arg) return mytrace import sys sys.settr…
Pdb also employs this approach for debug. I had wondered about pdb's implementation, when I saw it, I felt a little surprised.
Re: Tracing Python
#9Python has a built-in API for tracing: https://docs.python.org/3/library/sys.html#sys.settrace Here's an example of how to use it (obviously a minimal case, you can customise your handler do do whatever you need): def mytrace(frame, event, arg): if event == "call": print("call", frame.f_code.co_name, frame.f_locals) elif event == "return": print("return", frame.f_code.co_name, arg) return mytrace import sys sys.settr…
Wow, I can't believe I didn't know about this until now! I'm the lucky 10k[0] today.
Re: Tracing Python
#10I'll throw in my own too: https://github.com/kunalb/panopticon