[Tutor] Question about dictionary method get()

Francis Moore Francis.Moore at shaws.co.uk
Mon Jun 28 09:47:43 EDT 2004

From: Dick Moores [mailto:rdm at rcblue.com] 

> How do I "check for or propagate" None?

Checking for 'None' is as follows:

def func():
	d = {}
	d['a'] = 1
	d['b'] = 2
	d['c'] = 3

	if d.get('d') == None:
		print 'Key of "d" not found'
if __name__ == '__main__':

This will print 'Key of "d" not found'

I don't have my copy of Python In A Nutshell to hand to check the 
index for propogation of a value but I'm assuming that it means
to raise an exception. As the default implementation of the 
dictionary class does not raise an exception when a key is not 
found, you can raise your own. Like so:

	if d.get('d') == None:
		raise Exception, 'Key of "d" not found'

Someone more knowledgeable on the list might want to clarify that 
my general understanding of propagating 'None' is correct.

> Sorry for the basic questions.

No problem.

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