在引发异常后，python 回溯如何运行？

Question

I was surprised by the following behavior:

import traceback

raise Exception('dogs')
traceback.print_exc()
print('cat')

#=> Successfully prints traceback, doesn't print cat.

import traceback

raise Exception('dogs')
# traceback.print_exc()

print('cat')

#=> Also doesn't print cat.

So what exactly is going on here? What is the difference between the traceback.print_exc() module and print()? I found it surprising that apparently some functions can run after the exception is raised, but not others.

Any thoughts appreciated.

Thanks.

Answer 1

When an exception is raised, the control flow is changed. Unless you catch the exception, all the statements below the line where exception was raised won't get executed.

Traceback is used to print stack traces - https://docs.python.org/3/library/traceback.html

import traceback

try:
    raise Exception('dogs')
except:
    traceback.print_exc()
    print('cat')

Output:

In [5]: import traceback
   ...:
   ...: try:
   ...:     raise Exception('dogs')
   ...: except:
   ...:     traceback.print_exc()
   ...:     print('cat')
   ...:
Traceback (most recent call last):
  File "<ipython-input-5-3599c128a12e>", line 4, in <module>
    raise Exception('dogs')
Exception: dogs
cat