Mapping with continguous ranges of keys

Steve D'Aprano steve+python at
Thu Dec 15 12:06:25 EST 2016

I have some key:value data where the keys often are found in contiguous
ranges with identical values. For example:

{1: "foo",
 2: "foo",
 3: "foo",
 # same for keys 4 through 99
 100: "foo",
 101: "bar",
 102: "bar",
 103: "foobar",
 104: "bar",
 105: "foo", 

So in this case, the keys 1 through 100, plus 105, all have the same value.

I have about a million or two keys, with a few hundred or perhaps a few
thousand distinct values. The size of each contiguous group of keys with
the same value can vary from 1 to perhaps a hundred or so.

Has anyone dealt with data like this and could give a recommendation of the
right data structure to use?

The obvious way is to explicitly list each key, in a regular dict. But I
wonder whether there are alternatives which may be better (faster, more
memory efficient)?


“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.

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