更改 Python 循环中的步骤
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Changing step in Python loop
提问by David
In Python 2.7 I want to modify the step of a forloop in function of the specifics conditions satisfied in the loop. Something like this:
在 Python 2.7 中，我想在for循环中满足特定条件的函数中修改循环的步骤。像这样的东西：
step = 1
for i in range(1, 100, step):
if ...... :
step = 1
#do stuff
else:
step = 2
#do other stuff
but it seems that this can't be done, stepis always 1.
但似乎这不能做到，step总是1。
Thanks.
谢谢。
回答by OLIVER.KOO
you would need to increment stepmanually which can be done using a whileloop. checkout difference between whileand forloop.
您需要step手动递增，这可以使用while循环来完成。和loop之间的结帐差异whilefor。
The for statement iterates through a collection or iterable object or generator function.
The while statement simply loops until a condition is False.
for 语句遍历集合或可迭代对象或生成器函数。
while 语句只是循环，直到条件为 False。
if you use a whileloop your code would look something like this:
如果您使用while循环，您的代码将如下所示：
step = 1
i = 1
while i < 100:
if ...... :
step = 1
#do stuff
else:
step = 2
#do other stuff
i = i + step
回答by Nenad
You could do it with a while loop:
你可以用一个while循环来做到这一点：
step = 1
i = 1
while i < 100:
if ...... :
step = 1
#do stuff
else:
step = 2
#do other stuff
i+=step
回答by Jared Goguen
If you want to over-complicate things, you could create a custom generator where you can use the generator.sendmethod to pass in a new step during iteration.
如果您想让事情变得过于复杂，您可以创建一个自定义生成器，您可以在其中使用该generator.send方法在迭代过程中传入一个新步骤。
def variable_step_generator(start, stop=None, step=1):
if stop is None:
start, stop = 0, start
while start < stop:
test_step = yield start
if test_step is not None:
step = test_step
yield
start += step
With usage like:
用法如下：
variable_step_range = variable_step_generator(1, 100)
for i in variable_step_range:
print i
if i == 10:
variable_step_range.send(10)
if i == 90:
variable_step_range.send(1)
# 1, 2, 3, 4, 5, 6, 7, 8, 9,
# 10, 20, 30, 40, 50, 60, 70, 80, 90,
# 91, 92, 93, 94, 95, 96, 97, 98, 99
But this isn't really much more than a wrapper around the whileloop that the other answers suggest.
但这实际上只不过是while其他答案所建议的循环包装。
回答by Acccumulation
The second line of your code creates a range object that is then used for the rest of the loop, and your code doesn't modify that range object. And even if you did change the step, that wouldn't change just the next element of the range, it would change the whole range object (that is, changing the step to 2 would make everyelement in the range 2 more than the previous). If you really want to, you can create a named object and modify it within the for loop, but that would be a rather messy thing to do.
代码的第二行创建一个范围对象，然后用于循环的其余部分，并且您的代码不会修改该范围对象。即使您确实更改了步长，也不会只更改范围的下一个元素，而是会更改整个范围对象（即，将步长更改为 2 会使范围 2 中的每个元素都比前一个多）。如果你真的想要，你可以创建一个命名对象并在 for 循环中修改它，但这将是一件相当麻烦的事情。
You can also use another index separate from the main for loop one. For instance:
您还可以使用与主 for 循环分开的另一个索引。例如：
actual_index = 1
for for_loop_index in range(1,100):
if condition1:
actual_index = actual_index + 1
if condition2:
actual_index = actual_index + 2
if actual_index > 99:
break
This would basically be a while loop, except with a hard limit on the number of iterations, which could be useful in some use cases.
这基本上是一个 while 循环，除非对迭代次数有严格限制，这在某些用例中可能很有用。
回答by bieboebap
import numpy as np
for i in np.arange(start,stop,stepwidth):
# your stuff
回答by sainoba
You could add a skip check:
您可以添加跳过检查：
skip = 0
for i in range(1, 100):
if skip != 0:
skip -= 1
continue
if ...... :
#do stuff
else:
skip = 1
#do other stuff
