What is the usage of else: after a try/except clause

Question

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when is it necessary to add an else clause to a try..except in Python?
Python try-else

for arg in sys.argv[1:]:
    try:
        f = open(arg, 'r')
    except IOError:
        print 'cannot open', arg
    else:
        print arg, 'has', len(f.readlines()), 'lines'
        f.close()

What is usage of this else clause, and when will it be executed?

score 3 · Accepted Answer · answered Jun 23 '11 at 07:34

3

The try...except...else statement mean something like this :

try:
    # execute some code
except:
    # if code raises an error, execute this code
else:
    # if the "try" code did not raise an error, execute this code

answered Jun 23 '11 at 07:34

Cédric Julien

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2

The else is also not executed if there is a return in the try block. – Sylvain Defresne Jun 23 '11 at 07:37
There is a very good explanation of when it's useful to use a try-else here: http://stackoverflow.com/a/855764/621591 – Brendan Maguire Nov 15 '13 at 15:09

score 3 · Answer 2 · answered Jun 23 '11 at 07:36

From the Python documentation:

The optional else clause is executed if and when control flows off the end of the try clause.7.2 Exceptions in the else clause are not handled by the preceding except clauses.

Currently, control ``flows off the end'' except in the case of an exception or the execution of a return, continue, or break statement.

So the else clause is executed when the try does not not raise an exception and does not exit the block via control flow statement.

What is the usage of else: after a try/except clause

2 Answers2