[Newbie] error handling

[Fulvio]

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Hello there,

Simple question : how do I manage errors by the use "try/except" clause.
Example:
If I'd like to catch error coming from a function call that's using IMAP4
class, which error may raise such class?
In other words I've doubts about which error object I should put after
the "except" statement in order to trap the wanted error.

Is there, somehow, the way to list the errors from a class or function, prior
digging into the source?

F

 

[Bernard]

Hi Fulvio,

I often use this try except to find out about what type of errors might
happen in my code:
I use it when I really don't know what might happen.
try:
# do something
except:
print "Unexpected error:", sys.exc_info()[0]
continue

once it catches an error, just take a good look at the error message
and you'll be able to extend the try except like this:

try:
# do something
except KeyError:
print "this is a KeyError"
continue
except TypeError:
print "this is a TypeError"
continue
except:
print "Unexpected error:", sys.exc_info()[0]
os.system("pause")
continue

 

[Cameron Laird]

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Your mail has been scanned by InterScan MSS.
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Hello there,

Simple question : how do I manage errors by the use "try/except" clause.
Example:
If I'd like to catch error coming from a function call that's using IMAP4
class, which error may raise such class?
In other words I've doubts about which error object I should put after
the "except" statement in order to trap the wanted error.

Is there, somehow, the way to list the errors from a class or function, prior
digging into the source?

F

No.

It's an important question. No, there is NOT in general a way
to interrogate a class or function to determine the range of
exceptions it might throw.

Working programmers take a couple of approaches to analyze
exceptions:
A. Read documentation. Good API documentation
must specify exceptions thrown.

It's very, *very* rare for Python extensions
to document their exceptions accurately.
B. Incrementally refine your source. I might
write

try:
do_imap_stuff()
except:
raise

for my first round of coding. Then I exercise
a couple of use cases, and reach

try:
do_imap_stuff()
except IOError:
handle_this_exception()
except ZeroDivisionError:
handle_that_exception()
except:
raise

and so on.

Exceptions are hard to get right. I keep threatening to
write a book on the subject, mostly so I can learn what
the correct answers are.

 

[Bernard]

I just found this webpage showing the most common exceptions:
http://pydoc.org/1.5.2/exceptions.html

I hope this can help in some way.

 

[Gabriel Genellina]

I just found this webpage showing the most common exceptions:
http://pydoc.org/1.5.2/exceptions.html

Why not refer to the *current* documentation?
http://docs.python.org/lib/module-exceptions.html
(You already have it installed with Python)

1.5.2 is way too old!


--
Gabriel Genellina
Softlab SRL





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[Fulvio]

|Why not refer to the *current* documentation?

Gabriel,

Thank you, some time I (we) forget to look at the most obvious place
Meanwhile yesterday I found some useful info on the web, which an *except*
statement needs a string object or class for a named exception.
Now I got the meaning and " sys.exc_info()[0]" Bernard's idea is useful to
fish out more clues.

F

 

[Bernard]

lol you are so right! I didn't even notice this was the 1.5.2 version!