python: backtrace.hook does not work with backtrace.print

I can't figure out how to color a backtrace I print myself.
This colors my backtrace:

#!/bin/python3
import backtrace
backtrace.hook()
raise Exception('here')

But if I catch the exception and print it... then no color:

#!/bin/python3
import backtrace
backtrace.hook()
import traceback
try:
    raise Exception('here')
except Exception:
    traceback.print_exc()

I know these are 2 different packages, but they should be able to work together.
How do I catch and print exceptions (and a stack trace) in color?

CodePudding user response：

backtrace internally uses sys.excepthook do the trick. When an exception is raised and uncaught, the interpreter calls sys.excepthook with three arguments, the exception class, exception instance, and a traceback object. In your first case, when you call backtrace.hook(), the backtrace library essentially set the sys.excepthook to a custom function which can do all sorts of magic with the exception instance(coloring etc....)

>>> def custom_hook(*args):
...     print(args)
...
>>>
>>> import sys
>>> sys.excepthook = custom_hook
>>>
>>> 1 / 0 # No exception raised, instead it calls `custom_hook`
(<class 'ZeroDivisionError'>, ZeroDivisionError('division by zero'), <traceback object at 0x000001FA502B98C0>)

The excepthook does not call if the exception is raised and caught(using except).

>>> def custom_hook(*args):
...     print(args)
...
>>>
>>> import sys
>>> sys.excepthook = custom_hook
>>>
>>> try:
...     1 / 0 
... except: # Since the exception is caught here, it won't call `custom_hook`
...     pass
...

The exact scenario happened in your case. You have to re-raise the exception once it's caught to get the excepted behavior.