Question

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Python try-else

Comming from a Java background, I don’t quite get what the else clause is good for.

According to the docs

It is useful for code that must be
executed if the try clause does not
raise an exception.

But why not put the code after the try block? It seems im missing something important here…

Answer 1

The else clause is useful specifically because you then know that the code in the try suite was successful. For instance:

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()

You can perform operations on f safely, because you know that its assignment succeeded. If the code was simply after the try … except, you may not have an f.