Catch KeyError in Python

If it's raising a KeyError with no message, then it won't print anything. If you do...

try:    connection = manager.connect("I2Cx")except Exception as e:    print repr(e)

...you'll at least get the exception class name.

A better alternative is to use multiple except blocks, and only 'catch' the exceptions you intend to handle...

try:    connection = manager.connect("I2Cx")except KeyError as e:    print 'I got a KeyError - reason "%s"' % str(e)except IndexError as e:    print 'I got an IndexError - reason "%s"' % str(e)

There are valid reasons to catch all exceptions, but you should almost always re-raise them if you do...

try:    connection = manager.connect("I2Cx")except KeyError as e:    print 'I got a KeyError - reason "%s"' % str(e)except:    print 'I got another exception, but I should re-raise'    raise

...because you probably don't want to handle KeyboardInterrupt if the user presses CTRL-C, nor SystemExit if the try-block calls sys.exit().

I am using Python 3.6 and using a comma between Exception and e does not work. I need to use the following syntax (just for anyone wondering)

try:    connection = manager.connect("I2Cx")except KeyError as e:    print(e.message)

You should consult the documentation of whatever library is throwing the exception, to see how to get an error message out of its exceptions.

Alternatively, a good way to debug this kind of thing is to say:

except Exception, e:    print dir(e)

to see what properties e has - you'll probably find it has a message property or similar.