Asked  7 Months ago    Answers:  5   Viewed   21 times

How can I write a try/except block that catches all exceptions?

 Answers

62

You can but you probably shouldn't:

try:
    do_something()
except:
    print "Caught it!"

However, this will also catch exceptions like KeyboardInterrupt and you usually don't want that, do you? Unless you re-raise the exception right away - see the following example from the docs:

try:
    f = open('myfile.txt')
    s = f.readline()
    i = int(s.strip())
except IOError as (errno, strerror):
    print "I/O error({0}): {1}".format(errno, strerror)
except ValueError:
    print "Could not convert data to an integer."
except:
    print "Unexpected error:", sys.exc_info()[0]
    raise
Tuesday, June 1, 2021
 
csi
answered 7 Months ago
csi
19

There is no more elegant way of selectively "catching" nested exceptions. I suppose if you did this kind of nested exception catching a lot, you could possibly refactor the code into a common utility method. But it still won't be either elegant or efficient.

The elegant solution is to do away with the exception nesting. Either don't chain the exceptions in the first place, or (selectively) unwrap and rethrow the nested exceptions further up the stack.

Exceptions tend to be nested for 3 reasons:

  1. You have decided that the details of the original exception are unlikely to be useful for the application's error recovery ... but you want to preserve them for diagnostic purposes.

  2. You are implementing API methods that don't allow a specific checked exception but your code unavoidably throws that exception. A common workaround is to "smuggle" the checked exception inside an unchecked exception.

  3. You are being lazy and turning a diverse set of unrelated exceptions into a single exception to avoid having lots of checked exceptions in your method signature1.

In the first case, if you now need to discriminate on the wrapped exceptions, then your initial assumptions were incorrect. The best solution is change method signatures so that you can get rid of the nesting.

In the second case, you probably should unwrap the exceptions as soon as control has passed the problematic API method.

In the third case, you should rethink your exception handling strategy; i.e. do it properly2.


1 - Indeed, one of the semi-legitimate reasons for doing this has gone away due to the introduction of the multi-exception catch syntax in Java 7.

2 - Don't change your API methods to throws Exception. That only makes things worse. You now have to either "handle" or propagate Exception each time you call the methods. It is a cancer ...

Saturday, July 17, 2021
 
Eugenie
answered 5 Months ago
80

Try hooking up to the AppDomain.CurrentDomain.UnhandledException event as well.

Monday, August 2, 2021
 
Moz
answered 4 Months ago
Moz
55
try:
    [plot_pdf(f) for f in file_list]  # using list comprehensions
except:
    print ("Exception: ", sys.exc_info()[0])
    continue

If plot_pdf(f) throws an error during execution of comprehension, then, it is caught in the except clause, other items in comprehension won't be evaluated.

It is not possible to handle exceptions in a list comprehension, for a list comprehension is an expression containing other expression, nothing more (i.e. no statements, and only statements can catch/ignore/handle exceptions).

Function calls are expression, and the function bodies can include all the statements you want, so delegating the evaluation of the exception-prone sub-expression to a function, as you've noticed, is one feasible workaround (others, when feasible, are checks on values that might provoke exceptions, as also suggested in other answers).

More here.

Tuesday, August 10, 2021
 
brombeer
answered 4 Months ago
48

Just put the try/except block inside the loop. And there is no need in that pass statement at the end of the except block.

with open('list4.csv','wb') as f:
    writer = csv.writer(f)
    for s in sites:
        try:
            adrs = "http://turnpikeshoes.com/shop/" + str(s)
            driver = webdriver.PhantomJS()
            driver.get(adrs)
            time.sleep(5)
            LongDsc = driver.find_element_by_class_name("productLongDescription").text
            print "Working.." + str(s)
            writer.writerows([[LongDsc]])
        except:
            writer.writerows(['Error'])
            print ("Error Logged..")

NOTE It's generally a bad practice to use except without a particular exception class, e.g. you should do except Exception:...

Wednesday, November 24, 2021
 
PandemoniumSyndicate
answered 1 Week ago
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