生成器表达式与列表推导 [英] Generator expressions vs. list comprehensions

问题描述

何时应使用生成器表达式，何时应使用Python中的列表推导?

When should you use generator expressions and when should you use list comprehensions in Python?

# Generator expression
(x*2 for x in range(256))

# List comprehension
[x*2 for x in range(256)]

推荐答案

John的答案是很好的(列表理解是如果您想多次迭代某个对象，则效果更好).但是，还需要注意的是，如果要使用任何列表方法，都应使用列表.例如，以下代码将不起作用:

John's answer is good (that list comprehensions are better when you want to iterate over something multiple times). However, it's also worth noting that you should use a list if you want to use any of the list methods. For example, the following code won't work:

def gen():
    return (something for something in get_some_stuff())

print gen()[:2]     # generators don't support indexing or slicing
print [5,6] + gen() # generators can't be added to lists

基本上，如果您要做的只是迭代一次，则使用生成器表达式.如果要存储和使用生成的结果，则最好使用列表理解功能.

Basically, use a generator expression if all you're doing is iterating once. If you want to store and use the generated results, then you're probably better off with a list comprehension.

由于性能是选择一个以上的最常见原因，所以我的建议是不要担心它，而只选择一个即可.如果您发现程序运行速度太慢，那么只有这样，您才应该回去担心调整代码.

Since performance is the most common reason to choose one over the other, my advice is to not worry about it and just pick one; if you find that your program is running too slowly, then and only then should you go back and worry about tuning your code.

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