find non-empty value in a dictionary

[matthew]

hi,

say you have a dictionay d =
{'X': 0.0, 'Y'': 240.2, 'Z': 0.0, 'P': 13.3445}

where p divides pretty much evenly into Y; in this case approx 18

P will always be present and only one of X,Y,Z will have a non-zero value.

How can I easily find which X,Y, or Z is non-zero; esp. given that 
comparing floats is 'inaccurate' as in:

if X != 0:
	<stuff>
elif Y != 0:
	<stuff>
elif Z != 0:
	<stuff>
else:
	<stuff-up>

Also, once the correct axis is found,  exactly the same maths will be 
applied which means that in the above, the same statement will be 
replicated excepting the axis variable. any ideas on the best pythonic 
way to tackle this?

any hints on best practice with comparing floats.

Thanks. matthew.