为什么这本词典中有一个循环? [英] Why is there a loop in this dictionary?

问题描述

是否可以在字典旁边迭代列表?看起来很复杂.

Is it possible to iterate the list in side the dictionary? Looks like a complex syntax.

URLS = ['http://www.foxnews.com/',
    'http://www.cnn.com/',
    'http://europe.wsj.com/',
    'http://www.bbc.co.uk/',
    'http://some-made-up-domain.com/']

future_to_url = {executor.submit(load_url, url, 60): url for url in URLS}

推荐答案

您正在查看词典理解；它从循环中构建字典.

You are looking at a dictionary comprehension; it builds a dictionary from a loop.

等效于:

future_to_url = {}
for url in URLS:
    future_to_url[executor.submit(load_url, url, 60)] = url

但拼写更简洁.

可以执行相同的操作来生成列表:

The same can be done to produce a list:

[executor.submit(load_url, url, 60) for url in URLS]

或设置:

{executor.submit(load_url, url, 60) for url in URLS}

或在生成器表达式中延迟生成元素:

or produce the elements lazily in a generator expression:

(executor.submit(load_url, url, 60) for url in URLS)

请参见 列表理解部分以及更高版本，其中介绍了其他理解.

See the List Comprehensions section of the Python tutorial, and onwards, where the other comprehensions are explained.

对领域的理解需要Python 2.7或更高版本；如果需要将其移植回较早的Python版本，则可以在dict()函数内使用generator expression语法生成(key, value)元组:

Dict comprehensions require Python 2.7 or newer; if you need to port this back to older Python versions, you'd use the generator expression syntax inside a dict() function to produce (key, value) tuples:

dict((executor.submit(load_url, url, 60), url) for url in URLS)

这篇关于为什么这本词典中有一个循环?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！