Python: how to map the keys of a dictionary onto the values of another?

Question

Say you're working with these two dictionaries:

a={(1,2):1.8,(2,3):2.5,(3,4):3.9} #format -> {(x,y):value}
b={10:(1,2),20:(2,3),30:(3,4)} #format -> {id:(x,y)}

and you want to come up with a dictionary that has the following format: {id:value}. In this example, the result would be:

c={10:1.8,20:2.5,30:3.9}

I have tried the following

c={k:j for k in b.keys() and j in a.values()}

but the result is an apparently trivial

NameError: name 'j' is not defined

What's the best way of doing this? How do you "model" the correspondence?

Answer 1

Iterating over b only seems sufficient - why not just use the natural correspondence of the dict.

>>> {k: a[v] for k, v in b.items()}
{10: 1.8, 20: 2.5, 30: 3.9}

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A correct syntactical attempt at your idea would be something like

>>> {k:j for k, j in zip(b.keys(),a.values())}
{10: 1.8, 20: 3.9, 30: 2.5}

However as you can see, this doesn't work anyways. This is because dicts are of course unordered, and so there is no enforced relation between the keys of one dict and the values of another.