对于循环(新手) [英] For loops (novice)
问题描述
for y
,其中 y
只是一些列表。 $ b $
而for循环代表(i = 0; i <9; i (0,9,-2)
$ b可以表示为
$ b 假设不是一个常量增量,而是希望 i * = 2
,甚至 i * = i
。这是可能的,还是我不得不使用while循环呢?正如你所说,循环的一个迭代遍历元素的 一个列表。这个列表可以包含任何你喜欢的东西,所以你可以事先构建一个包含每一步的列表。
A for
循环也可以遍历生成器,这是一小段代码,而不是实际的列表。在Python中, range()
实际上是一个生成器(在Python 2.x中, range()
而 xrange()
是生成器。)
例如:
$
$ b $ in doubler(1):
print i
上面的代表
循环会打印
1
2
4
8
等等,直到您按下Ctrl + C。
I recently started learning Python, and the concept of for loops is still a little confusing for me. I understand that it generally follows the format for x in y
, where y
is just some list.
The for-each loop for (int n: someArray)
becomes for n in someArray
,
And the for loop for (i = 0; i < 9; i-=2)
can be represented by for i in range(0, 9, -2)
Suppose instead of a constant increment, I wanted i*=2
, or even i*=i
. Is this possible, or would I have to use a while loop instead?
解决方案 As you say, a for
loop iterates through the elements of a list. The list can contain anything you like, so you can construct a list beforehand that contains each step.
A for
loop can also iterate over a "generator", which is a small piece of code instead of an actual list. In Python, range()
is actually a generator (in Python 2.x though, range()
returned a list while xrange()
was the generator).
For example:
def doubler(x):
while True:
yield x
x *= 2
for i in doubler(1):
print i
The above for
loop will print
1
2
4
8
and so on, until you press Ctrl+C.
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