在Python中查找快速默认别名

Question

Is there a faster way to do the following for much larger dicts?

aliases = {
            'United States': 'USA',
            'United Kingdom': 'UK',
            'Russia': 'RUS',
          }
if countryname in aliases: countryname = aliases[countryname]

Answer 1

Your solution is fine, as "in" is 0(1) for dictionaries.

You could do something like this to save some typing:

countryname = aliases.get(countryname, countryname)

(But I find your code a lot easier to read than that)

When it comes to speed, what solution is best would depend on if there will be a majority of "hits" or "misses". But that would probably be in the nanosecond range when it comes to difference.

Answer 2

If your list fits in memory, dicts are the fastest way to go. As S.Mark points out, you are doing two lookups where one will do, either with:

countryname = aliases.get(countryname, countryname)

(which will leave countryname unchanged if it isn't in the dictionary), or:

try:
    countryname = aliases[countryname]
except KeyError:
    pass

Answer 3

Accessing with .get could be faster than checking and assigning in variable

aliases.get(countryname)

And if countryname is not exists in aliases it will return None.

Answer 4

If your dictionary is very large and you expect many of your checks not to find a match, then you might want to consider a Bloom filter or one of it's derivatives and allow false positives.

Alternatively, because your keys can be sorted (and/or have a derived values), you could implement a bisection or other root-finding algorithm.

First, I'd figure out exactly how Python implements dictionary look-ups, so you are not just re-inventing the wheel.

Also, a pure-Python implementation of these could be quite slow if it involves a lot of iteration. Consider Cython, Numpy, or F2Py to get truly optimized.

(if you are dealing with just country names, then I don't think you are dealing with mappings large enough to warrant any of my suggestions), but if you are looking at doing some kind of spell-check implementation, then..

Good luck.