在上下文管理器中捕获异常

Question

Trying to understand how I should catch/handle exceptions of a context manager:

import contextlib
import urllib

with contxtlib.closing( urllib.request.urlopen(some_url) ) as resp:
    return resp.read()

I know that upon exiting the context manager, even if any errors occurred, the context manager will close. For the example above, how could I catch the closing and urlopen exceptions given that they are within a context manager? Is there a way for me to use try... except to catch and handle all exceptions for both closing and urlopen ?

Answer 1

from contextlib import closing
from urllib.request import urlopen
from urllib.error import HTTPError, URLError

try:
    with closing(urlopen(some_url)) as resp:
        return resp.read()
except (HTTPError, URLError, Exception) as err:
    print(err)
    # handle exception(s)

The contextlib.closing() context manager calls the close() method. As can be seen in the docs , you do not have to explicitly close it yourself (replaced page with obj for context):

Even if an error occurs, obj.close() will be called when the with block is exited.

For the urllib.request.urlopen , see the approaches on catching HTTPError or URLError with urlopen

Follow-up reading:

• PEP 343 -- The "with" Statement: https://www.python.org/dev/peps/pep-0343/
• https://stackoverflow.com/a/57280764/6003691