creepy design in python

Question

can somebody help me with the following piece of the code:

try:
    #do some things
    myClass.close()
except Exception, error:
    myClass.close()
    raise error

as You see I can't use here finally because in that case I will not know if an error actually occured, and I need to raise this error (raise error)

my question is how can I avoid using this two times myClass.close()? thanks in advance for any help

Please **never** re-raise exception in this way. **Always** use a plain `raise` for this purpose. Otherwise you lose the original backtrace which is pretty annoying in most cases. — ThiefMaster, Sep 11 '11 at 16:31

score 2 · Answer 1 · answered Sep 11 '11 at 16:27

2

You can use finally :)

This should do what you want:

try:
    #do some things
finally:
    myClass.close()

answered Sep 11 '11 at 16:27

Wolph

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ok, but in that case, how will I receive an indication that an exception was raised? – yeap Sep 11 '11 at 16:34
3

@yeap: The exception will automatically be re-raised after the `finally` block finishes (if there was one). – Dietrich Epp Sep 11 '11 at 16:41

score 2 · Accepted Answer · answered Sep 11 '11 at 16:28

2

This is equivalent to your code:

try:
    #do some things
finally:
    myClass.close()

First it calls myClass.close() and if there was a error it is raised again.

You can also have this to handle specific exceptions:

try:
    #do some things
except Exception, error:
    raise # re-raise the original exception
finally:
    myClass.close()

answered Sep 11 '11 at 16:28

Jochen Ritzel

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Use only `raise` to re-raise the exception instead of using `raise error` to keep the backtrace of the original exception. – ThiefMaster Sep 11 '11 at 16:32
What happens if the close itself raises an exception in the various cases (e.g. - an exception was already raised in the try block)? Can / should you wrap the close inside the finally block in another try block that swallows any / all exceptions the close raises? Will that preserve the previous exception raised in the original try block? – jschultz410 Nov 05 '19 at 22:11

score 1 · Answer 3 · answered Sep 11 '11 at 16:28

1

You can chain try, except and finally since Python 2.5:

try:
    # Do some things...
    pass
except Exception, error:
    # Log the error...
    raise
finally:
    myClass.close()

answered Sep 11 '11 at 16:28

Frédéric Hamidi

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Use only `raise` instead of `raise error` to keep the backtrace of the original exception. – ThiefMaster Sep 11 '11 at 16:32
@ThiefMaster, you're absolutely right. Answer updated, thanks for the heads-up :) – Frédéric Hamidi Sep 11 '11 at 16:34

score 1 · Answer 4 · answered Sep 11 '11 at 16:29

1

Next to a finally (that would work) you could also use a context manager that calls your myClass.close() method on exit.

answered Sep 11 '11 at 16:29

martinfischer

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score 0 · Answer 5 · answered Sep 11 '11 at 16:27

0

Nest it.

try:
  try:
    ...
  except ...:
    raise error
finally:
  myClass.close()

answered Sep 11 '11 at 16:27

Ignacio Vazquez-Abrams

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1

Same thing here - use `raise` instead of `raise whatever` to re-raise an exception. – ThiefMaster Sep 11 '11 at 16:32

score 0 · Answer 6 · edited May 23 '17 at 11:47

0

Regardless this will not work. If you already raised an exception/error the first time you invoked myClass.close(), calling it again will be of no help. The error handling keywords are for implementing fallbacks, reporting and routing of the error-flow.

See here for error handling: Can I get the exception from the finally block in python?

edited May 23 '17 at 11:47

Community

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answered Sep 11 '11 at 16:33

Lorenz Lo Sauer

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creepy design in python

6 Answers6