在python中使用自定义步骤循环 [英] For loop with custom steps in python

问题描述

我可以在 python 中创建简单的 for 循环，例如:

I can make simple for loops in python like:

for i in range(10):

然而，我不知道如何制作更复杂的，这在 C++ 中真的很容易.

However, I couldn't figure out how to make more complex ones, which are really easy in c++.

你将如何在 python 中实现这样的 for 循环:

How would you implement a for loop like this in python:

for(w = n; w > 1; w = w / 2)

迄今为止我制作的最接近的一个是:

The closest one I made so far is:

for w in reversed(range(len(list)))

推荐答案

首先也是最重要的:Python for 循环与 C for 循环实际上并不是一回事.它们是 For Each 循环.您迭代可迭代的元素.range() 生成一个可迭代的整数序列，让您模拟最常见的 C for 循环用例.

First and foremost: Python for loops are not really the same thing as a C for loop. They are For Each loops instead. You iterate over the elements of an iterable. range() generates an iterable sequence of integers, letting you emulate the most common C for loop use case.

然而，大多数时候您不想想要使用range().您将遍历列表本身:

However, most of the time you do not want to use range(). You would loop over the list itself:

for elem in reversed(some_list):
    # elem is a list value

如果必须要有索引，通常使用enumerate()将其添加到循环中:

If you have to have a index, you usually use enumerate() to add it to the loop:

for i, elem in reversed(enumerate(some_list)):
    # elem is a list value, i is it's index in the list

对于真正时髦"的循环，使用 while 或创建您自己的生成器函数:

For really 'funky' loops, use while or create your own generator function:

def halved_loop(n):
    while n > 1:
        yield n
        n //= 2

for i in halved_loop(10):
    print i

打印10、5、2.您也可以将其扩展到序列:

to print 10, 5, 2. You can extend that to sequences too:

def halved_loop(sequence):
    n = -1
    while True:
        try:
            yield sequence[n]
        except IndexError:
            return
        n *= 2

for elem in halved_loop(['foo', 'bar', 'baz', 'quu', 'spam', 'ham', 'monty', 'python']):
    print elem

打印:

python
monty
spam
foo

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