为什么Python没有“continue if”语句？

This is a pretty readable chunk of code I think,

我认为这是一个非常易读的代码块，

for i in range(100):
    continue if i % 2 == 0

But it's not syntactically correct. We can do other nice things in Python like,

但它在语法上并不正确。我们可以在Python中做其他好事，比如

for i in things:
    total += 3 if i % 2 == 0 else 1

Or maybe,

或者可能，

return a if b > a else c

Why can't we do a continue if statement?

为什么我们不能继续if声明？

3 个解决方案

#1

The flow:

流程：

for i in range(100):
    continue if i % 2 == 0

Would be equivalent to:

相当于：

for i in range(1, 100, 2):
    ...

Or, more generically, to:

或者，更一般地说，：

for i in range(100):
    if i % 2 == 0:
        continue

Python language designers have a history of voting against changes to the grammar which are only offering slightly different ways of doing the same thing ("There should be one obvious way to do it").

Python语言设计者有一个投票反对语法变化的历史，它只提供了略微不同的方法来做同样的事情（“应该有一种明显的方法来做”）。

The type of one-liner construct which you've mentioned

您提到的单线构造的类型

x if cond else y

was an exception made, here. It was added to the language to offer a less error-prone way of achieving what many users were already attempting to achieve with and and or short-circuiting hacks (source: Guido). Code in the wild was using:

这是一个例外。它被添加到语言中，以提供一种不易出错的方式来实现许多用户已经尝试使用和/或短路黑客（来源：Guido）。野外代码使用：

cond and x or y

Which is not logically equivalent, yet it's an easy mistake to make for users who were already familiar with the ternary cond ? : x : y syntax from C. A correct equivalent is:

这在逻辑上是不相同的，但对于已经熟悉三元cond的用户来说，这是一个容易犯的错误？：来自C的x：y语法。正确的等价物是：

(cond and [x] or [y])[0]

But, that's ugly. So, the rationale for the addition of an expression x if cond else y was stronger than a mere convenience.

但是，这很难看。因此，如果加上其他y，则添加表达式x的基本原理强于仅仅是方便。

#2

Because x if cond else y is actually an expression. Expressions are statements which evaluate to a value, in this case, either x or y.

因为x if cond else y实际上是一个表达式。表达式是对值进行求值的语句，在本例中为x或y。

continue is not a value, so there's that. Also,

继续不是一个价值，所以就是这样。也，

if cond:
    continue

is really not much harder or more "error prone" than continue if cond, whereas v = x if cond else y is probably better than

实际上并没有比cond更难或更容易出错，而v = x如果cond else y可能比

if cond:
    v = x
else:
    v = y

There's also the fact that if we allowed continue if cond, we add a new way to use this _ if cond pattern, i.e. we allow it without an else.

还有一个事实是，如果我们允许继续cond，我们添加一种新方法来使用这个_如果cond模式，即我们允许它没有其他。

For more info: https://docs.python.org/2.5/whatsnew/pep-308.html

有关更多信息：https：//docs.python.org/2.5/whatsnew/pep-308.html

#3

Python does have such a thing, the syntax is just a bit different. Instead of the "if and "continue" being combined as one statement, they are separated into a conditional statement (if, while etc), and a control flow (continue, pass, break etc) if it evaluates to true. In your first code example, the syntax would be:

Python确实有这样的东西，语法有点不同。而不是将“if和”继续“组合为一个语句，如果它的计算结果为true，则将它们分为条件语句（if，while等）和控制流（continue，pass，break等）。代码示例，语法为：

for i in range(100):
    if i % 2 == 0:
        continue
    else:
        #you could also add an else like this do something else if the 
        #number evaluated to odd

This will move on to the next iteration of the outer loop.There are also other helpful iteration tools like this, called "Control Flow Tools." I'll include a link to the Python docs that explain this. There's a ton of useful stuff there, so please do have a look.

这将继续进行外循环的下一次迭代。还有其他有用的迭代工具，称为“控制流工具”。我将包含一个解释这个的Python文档的链接。那里有很多有用的东西，所以请看看。

Others here have also suggested a single-line syntax, which works too. It is, however, good to understand both approaches; this way you can keep your code as simple as possible, but you'll also have the ability to nest loops and conditions if your algorithm will benefit from it.

这里的其他人也提出了单行语法，它也有效。然而，了解这两种方法是有益的;通过这种方式，您可以使代码尽可能简单，但如果您的算法将从中受益，您还可以嵌套循环和条件。

Happy coding!

快乐的编码！

https://docs.python.org/3/tutorial/controlflow.html

#1