如何退出if子句

Question

过早退出if条款有哪些方法？

有时我正在编写代码并希望break在if子句中放置一个语句,只记住那些只能用于循环.

让我们以下面的代码为例:

if some_condition:
   ...
   if condition_a:
       # do something
       # and then exit the outer if block
   ...
   if condition_b:
       # do something
       # and then exit the outer if block
   # more code here

我可以想到一种方法:假设退出情况发生在嵌套的if语句中,将剩余的代码包装在一个大的else块中.例:

if some_condition:
   ...
   if condition_a:
       # do something
       # and then exit the outer if block
   else:
       ...
       if condition_b:
           # do something
           # and then exit the outer if block
       else:
           # more code here

这样做的问题是更多的退出位置意味着更多的嵌套/缩进代码.

或者,我可以编写我的代码,使if条款尽可能小,不需要任何退出.

有没有人知道退出if条款的好/更好的方法？

如果有任何关联的else-if和else子句,我认为退出会跳过它们.

Answer 1

(此方法适用于ifs,多个嵌套循环和其他您无法break轻松完成的构造.)

将代码包装在自己的函数中.而不是break,使用return.

例:

def some_function():
    if condition_a:
        # do something and return early
        ...
        return
    ...
    if condition_b:
        # do something else and return early
        ...
        return
    ...
    return

if outer_condition:
    ...
    some_function()
    ...

Answer 2

from goto import goto, label

if some_condition:
   ...
   if condition_a:
       # do something
       # and then exit the outer if block
       goto .end
   ...
   if condition_b:
       # do something
       # and then exit the outer if block
       goto .end
   # more code here

label .end

(请不要实际使用它.)

Answer 3

while some_condition:
   ...
   if condition_a:
       # do something
       break
   ...
   if condition_b:
       # do something
       break
   # more code here
   break

Answer 4

您可以使用例外模拟goto的功能:

try:
    # blah, blah ...
    # raise MyFunkyException as soon as you want out
except MyFunkyException:
    pass

免责声明:我的意思是提醒您注意以这种方式做事的可能性,而在正常情况下我绝不认为这是合理的.正如我在关于这个问题的评论中提到的那样,构建代码以便首先避免拜占庭条件是可取的.:-)

Answer 5

可能是这个吗？

if some_condition and condition_a:
       # do something
elif some_condition and condition_b:
           # do something
           # and then exit the outer if block
elif some_condition and not condition_b:
           # more code here
else:
     #blah
if

Answer 6

一般来说，不要。如果您嵌套“如果”并打破它们，那么您就做错了。

但是，如果您必须：

if condition_a:
   def condition_a_fun():
       do_stuff()
       if we_wanna_escape:
           return
   condition_a_fun()
if condition_b:
   def condition_b_fun():
       do_more_stuff()
       if we_wanna_get_out_again:
           return
   condition_b_fun()

请注意，这些函数不必在 if 语句中声明，它们可以提前声明；）这将是一个更好的选择，因为它将避免稍后需要重构丑陋的 if/then。

Answer 7

对于实际提出的要求，我的方法是将这些ifs放入一个单循环的循环中

while (True):
    if (some_condition):
        ...
        if (condition_a):
            # do something
            # and then exit the outer if block
            break
        ...
        if (condition_b):
            # do something
            # and then exit the outer if block
            break
        # more code here
    # make sure it is looped once
    break

测试一下：

conditions = [True,False]
some_condition = True

for condition_a in conditions:
    for condition_b in conditions:
        print("\n")
        print("with condition_a", condition_a)
        print("with condition_b", condition_b)
        while (True):
            if (some_condition):
                print("checkpoint 1")
                if (condition_a):
                    # do something
                    # and then exit the outer if block
                    print("checkpoint 2")
                    break
                print ("checkpoint 3")
                if (condition_b):
                    # do something
                    # and then exit the outer if block
                    print("checkpoint 4")
                    break
                print ("checkpoint 5")
                # more code here
            # make sure it is looped once
            break

Answer 8

还有另一种方法，它不依赖于定义函数（因为有时对于小代码片段来说可读性较差），不使用额外的外部 while 循环（这可能需要在注释中进行特别欣赏，以便第一眼就能理解） ，不使用 goto (...)，最重要的是让你保持外部的缩进级别，这样你就不必开始嵌套东西。

if some_condition:
   ...
   if condition_a:
       # do something
       exit_if=True # and then exit the outer if block
if some condition and not exit_if: # if and only if exit_if wasn't set we want to execute the following code
   # keep doing something
   if condition_b:
       # do something
       exit_if=True # and then exit the outer if block
if some condition and not exit_if:
   # keep doing something

是的，这还需要重新考虑可读性，但是，如果代码片段很小，则不需要跟踪任何永远不会重复的 while 循环，并且在了解中间 if 的用途后，它很容易阅读，全部都在一处且具有相同的缩进。

而且它应该非常有效。