Using a range as a dictionary index in Python [duplicate]

Question

Is it possible to do something like:

r = {range(0, 100): 'foo', range(100, 200): 'bar'}

print r[42]

> 'foo'

So I would like to use a numeric range as part of a dictionary index. To make things more complicated I would also like to use multi-indexes like ('a', range(0,100)). So the concept should be ideally expandable to that. Any suggestions?

A similar question was asked as here, but I am interested in a comprehensive implementation as opposed to the different approaches of that question.

Answer 1

As an alternative approach, if you are trying to look up values associated with certain ranges you could use the built in Python bisect library as follows:

import bisect

def boundaries(num, breakpoints=[100, 200], result=['foo', 'bar']):
    i = bisect.bisect(breakpoints, num-1)
    return result[i]

print boundaries(42)

This would display:

foo

Answer 2

If you are on Python 3.x you can use a range object as key but to retrieve a value you will do something like this:

In [33]: r = {range(0, 100): 'foo', range(100, 200): 'bar'}

In [34]: { r[key] for key in r if 42 in key}
Out[34]: {'foo'}

The reason you can't do this in Python2.x is because the range function in version 2.7 onwards returns a list and lists cannot be used as dictionary keys because they do not provide a valid __hash__ method.