On Thu, 12 Jul 2012 14:20:18 +0100, andrea crotti wrote:
> One thing that I don't quite understand is why some calls even if I
> catch the exception still makes the whole program quit.
Without seeing your whole program, we can't possibly answer this. But by
consulting my crystal ball, I bet you have something like this:
try:
do_stuff() # run your program
except Exception as e:
# pointlessly catch exceptions I can't handle, which has the
# bonus of making debugging MUCH MUCH harder
print("here")
# end of file, nothing further to do
When do_stuff() fails, "here" gets printed, and then the program exits
because there's nothing else to do.
Catching exceptions doesn't magically cause the code to continue from the
point of the error. It doesn't work like that. Execution skips from where
the error occurred to the except clause. Once the except clause has run,
anything following the except clause runs, and then the program ends as
normal.
If you haven't already done so, I recommend you go through the tutorial:
http://docs.python.org/py3k/tutorial/index.html
in particular the part about exception handling:
http://docs.python.org/py3k/tutorial/errors.html
> For example this
>
> try:
> copytree('sjkdf', 'dsflkj')
> Popen(['notfouhd'], shell=True)
> except Exception as e:
> print("here")
What is "Popen" and where is it from?
My first guess was os.popen, but that doesn't take a shell argument:
py> os.popen(['ls', '-l'], shell=True)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: popen() got an unexpected keyword argument 'shell'
> behaves differently from:
>
> try:
> Popen(['notfouhd'], shell=True)
> copytree('sjkdf', 'dsflkj')
> except Exception as e:
> print("here")
>
> because if copytree fails it quits anyway.
Well of course it does. If copytree fails, the try block ends and
execution skips straight to the except block, which runs, and then the
program halts because there's nothing else to be done.
That at least is my guess, based on the described symptoms.
--
Steven
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