对列表中所有项目传递功能的最快方法

Question

I have a list of about 50,000 or so words, and I want to pass a function on each item in the list. Then I want to save the original word as a key, and the translated word as the respective value in a dictionary. Right now I know I can do this:

translations = {word: translate(word) for word in word_list}

But this takes too long I think. Is there a faster way this can be accomplished?

Answer 1

Mapping functions should work faster than dict comprehensions:

translations = dict(zip(word_list, map(translate, word_list)))

What happens here is:

• We apply the function to each element in word_list , returning a map object
• Combine it into a sequence ( zip object) of one-to-one element tuples from the original list and that map object
• Convert the resulting sequence into a dictionary

After setting up a test program, it appears that there is a slight performance improvement. This is the code:

from datetime import datetime
def translate(wo):
    return wo.upper()

word_list = {str(i):str(i+1) for i in range(50000)}
d = datetime.now()
translations = dict(zip(word_list, map(translate, word_list)))
print(datetime.now() - d)
d = datetime.now()
translations = {word: translate(word) for word in word_list}
print(datetime.now() - d)

After a few runs, the second printed time is always greater than the first one, which proves the efficiency.

Answer 2

If you only need few values, and won't iterate over the dict, you can try doing it lazily:

class MyDefaultDict(dict):
    def __init__(self, word_iterable, translate):
        self.word_set = frozenset(word_iterable)
        self.translate = translate
    def __missing__(self, key):
        if key in self.word_set:
            translated = translate(key)
            self[key] = translated
            return translated
        raise KeyError(key)