Re: [Tutor] question about try except
and i am using some try / except statements. the problem is, that even though my script does not crash, i dont know the exact error. IT sounds like your try/except is masking the error. Its usually a good idea to NOT Use try/except when developing your code, then go back and put it in when the basics are working. That way Pythons own exception handling will catch the error, force a break and print the stacktrace whoich helps identify the problem. is there a parameter that will allow me to use try and except but that will also pring out the traceback statements that python usually does to the terminal? One technique is to simply call raise within each exception block, then comment out the raise lines when you no longer need them. HTH, Alan G Author of the learn to program web tutor http://www.freenetpages.co.uk/hp/alan.gauld ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] question about try except
nephish wrote:
Hey there,
i am writing some (for me) pretty complicated stuff for work that
really needs to work.
i have looked at exception handling in the Learning Python book.
and i am using some try / except statements.
the problem is, that even though my script does not crash, i dont know
the exact error.
is there a parameter that will allow me to use try and except but that
will also pring out the traceback statements that python usually does to
the terminal?
If you put traceback.print_exc() in your exception handler it will print out
the exception string and the full stack trace. This is very handy when you have
unexpected exceptions as it will let you know where the problem occurs.
For example:
try:
open('foo.txt')
except IOError:
import traceback
traceback.print_exc()
Kent
--
http://www.kentsjohnson.com
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Re: [Tutor] question about try except
On 10/26/05, nephish [EMAIL PROTECTED] wrote: Yeah, cool. i am just starting this part. i am glad i started with python. thanks for the help if your app is willing to tolerate errors/crashes, then i would take alan's advice and just letting the errors happen, as opposed to being so careful with (and integrating Kent's suggestion for the full traceback with): try: BLOCK except Exception, e: print e, traceback.print_exc() # take some other evasive yet safe maneuver i only use the above when integrating into large systems (that aren't supposed to crash, that need some cleanup, and/or that need to take other action). otherwise for simple scripts, i just let the darn thing crash out and add in the handler for those errors. cheers, -- wesley - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Core Python Programming, Prentice Hall, (c)2006,2001 http://corepython.com wesley.j.chun :: wescpy-at-gmail.com cyberweb.consulting : silicon valley, ca http://cyberwebconsulting.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] question about try except
w chun wrote: if your app is willing to tolerate errors/crashes, then i would take alan's advice and just letting the errors happen, as opposed to being so careful with (and integrating Kent's suggestion for the full traceback with): try: BLOCK except Exception, e: print e, traceback.print_exc() # take some other evasive yet safe maneuver No, not quite. print_exc() does its own output and returns None, so it shouldn't be part of the print statement. And print_exc() prints e as part of its output, so 'print e' is redundant. All you need in the except block is traceback.print_exc() and whatever additional handling you want to do. Normally it's not a good idea to catch generic Exception - you usually can be more focused than that - but at a high level in an application it can be useful to catch everything. For example you may be processing a list of files in a loop and you don't want an error in one file to abort the loop. So you put a try / except at the top level of the loop to catch and log errors, then continue with the next file. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] question about try except
Yes, You can catch an error object along with the exception, as in: try: fileo = open(nofile) except IOError, e: print Alas..., e As you see, the error object has a string representation equal wo what normally the python interpreter prints... Alas... [Errno 2] No such file or directory: 'nofile' Hope it helps. It took me originally a long time to know this trick, as it's kinda buried in the docs. Hugo nephish wrote: Hey there, i am writing some (for me) pretty complicated stuff for work that really needs to work. i have looked at exception handling in the Learning Python book. and i am using some try / except statements. the problem is, that even though my script does not crash, i dont know the exact error. is there a parameter that will allow me to use try and except but that will also pring out the traceback statements that python usually does to the terminal? thanks ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] question about try except
Thanks Hugo, Now that i know where to look appreciate your help. -sk On Wed, 2005-10-26 at 21:27 -0600, Hugo González Monteverde wrote: Yes, You can catch an error object along with the exception, as in: try: fileo = open(nofile) except IOError, e: print Alas..., e As you see, the error object has a string representation equal wo what normally the python interpreter prints... Alas... [Errno 2] No such file or directory: 'nofile' Hope it helps. It took me originally a long time to know this trick, as it's kinda buried in the docs. Hugo nephish wrote: Hey there, i am writing some (for me) pretty complicated stuff for work that really needs to work. i have looked at exception handling in the Learning Python book. and i am using some try / except statements. the problem is, that even though my script does not crash, i dont know the exact error. is there a parameter that will allow me to use try and except but that will also pring out the traceback statements that python usually does to the terminal? thanks ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] question about try except
i am writing some (for me) pretty complicated stuff for work that really needs to work. i have looked at exception handling... and i am using some try / except statements. the problem is, that even though my script does not crash, i dont know the exact error. is there a parameter that will allow me to use try and except but that will also pring out the traceback statements that python usually does to the terminal? exception handling is one of the greatest strengths of Python and other high-level languages with this feature. it allows the programmer to anticipate potential problems and perhaps be able to accept and process them at runtime. let's say you have a code block called BLOCK. newbies to Python would typically do something like this to ensure that errors don't happen: try: BLOCK except: pass however, this is not the case. if errors *do* happen, they are thrown away, thus serves no one any good, not the programmer nor the user. the best solution is to catch specific exceptions and handle each case. (sure, and having just one handler for multiple exceptions is also okay.). one example is hugo's where he catches an IOError exception and uses the exception instance 'e' to get more info out of it. now if you *don't* know what exceptions may happen, you can do something similar. it's almost a combination of the above two handlers: try: BLOCK except Exception, e: print 'Caught exception without a specific handler:, e this will at least tell you what exception happens in BLOCK, so that you can modify it to be something like: try: BLOCK except YourSpecificException, e: # handle YourSpecificException code except Exception, e: print 'Caught exception without a specfic handler:', e once you know the range of exceptions that may happen in BLOCK and have written handlers for them, you can dispense with the general catch-all. hope this helps! -- wesley - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Core Python Programming, Prentice Hall, (c)2006,2001 http://corepython.com wesley.j.chun :: wescpy-at-gmail.com cyberweb.consulting : silicon valley, ca http://cyberwebconsulting.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] question about try except
Yeah, cool. i am just starting this part. i am glad i started with python. thanks for the help sk On Wed, 2005-10-26 at 21:32 -0700, w chun wrote: i am writing some (for me) pretty complicated stuff for work that really needs to work. i have looked at exception handling... and i am using some try / except statements. the problem is, that even though my script does not crash, i dont know the exact error. is there a parameter that will allow me to use try and except but that will also pring out the traceback statements that python usually does to the terminal? exception handling is one of the greatest strengths of Python and other high-level languages with this feature. it allows the programmer to anticipate potential problems and perhaps be able to accept and process them at runtime. let's say you have a code block called BLOCK. newbies to Python would typically do something like this to ensure that errors don't happen: try: BLOCK except: pass however, this is not the case. if errors *do* happen, they are thrown away, thus serves no one any good, not the programmer nor the user. the best solution is to catch specific exceptions and handle each case. (sure, and having just one handler for multiple exceptions is also okay.). one example is hugo's where he catches an IOError exception and uses the exception instance 'e' to get more info out of it. now if you *don't* know what exceptions may happen, you can do something similar. it's almost a combination of the above two handlers: try: BLOCK except Exception, e: print 'Caught exception without a specific handler:, e this will at least tell you what exception happens in BLOCK, so that you can modify it to be something like: try: BLOCK except YourSpecificException, e: # handle YourSpecificException code except Exception, e: print 'Caught exception without a specfic handler:', e once you know the range of exceptions that may happen in BLOCK and have written handlers for them, you can dispense with the general catch-all. hope this helps! -- wesley - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Core Python Programming, Prentice Hall, (c)2006,2001 http://corepython.com wesley.j.chun :: wescpy-at-gmail.com cyberweb.consulting : silicon valley, ca http://cyberwebconsulting.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
