python how to create list of interchangeable values?

Question

I'm working with midi note, midi number, and frequency. What kind of list in python should I use to refer to any one attribute and get the other attributes?

for example:

• input: "C3", return frequency and get 261.6255653006.

• input: 261.6255653006, return midinumber and get 60

• input: 60, return midinote and get "C3"

what syntax, functions, objects, or list type would I use?

Answer 1

Like I said in the comments, a dictionary of tuples is what you're probably looking for. Example:

data = {'C3': ('frequency', 261.6255653006), 
    261.6255653006: ('midinumber', 60), 
    60: ('midinote', 'C3'),
}

To validate your input you can do:

input = raw_input()
try:
    key = float(input)
except ValueError:
    key = input

try:
    value = data[key]
except KeyError:
    print "Invalid input. Valid keys are: " + ', '.join(data.keys())
else:
    #input was valid, so value == data[key]

Tuples are indexed just like lists are. However, they are immutable which means you can't change them or append new items to them. And I believe that's desired in your case.

Dictionaries are indexed by keys, for example data['C3'] returns ('frequency', 261.6255653006) and data['C3'][0] returns 'frequency'.