如何在python中创建``空if语句'' [英] How to create an 'empty if statement' in python

问题描述

在C语言中非常常见:像这样黑客空if语句":

It's very common in C: hacking 'empty if statement' like this:

if(mostlyhappencondition)
    ;#empty statement
else{
    dosomething;
}

它在Python中工作吗?我的意思是，我们可以通过使用它来提高应用程序的性能吗?我也想知道为什么.

It's working in Python? I mean, can we improve the app's performance by using that? I'd also like to know why.

推荐答案

如果"if"中没有else情况，则会提高性能，因为字节码不会将执行传递给"if"情况.

There is a performance improvement if there isn't an else case in the "if", since the bytecodes don't pass execution into the "if" case.

有些功能和dis.dis(foo)

以下示例应用程序:

def foo(x):
    if x:
        pass
    else:
        return x+2

反汇编为:

5           0 LOAD_FAST                0 (x)
            3 POP_JUMP_IF_FALSE        9

6           6 JUMP_FORWARD             8 (to 17)

8     >>    9 LOAD_FAST                0 (x)
           12 LOAD_CONST               1 (2)
           15 BINARY_ADD          
           16 RETURN_VALUE        
      >>   17 LOAD_CONST               0 (None)
           20 RETURN_VALUE        

以下

def foo(x):
    if not x:
        return x+2

反汇编为:

11           0 LOAD_FAST                0 (x)
             3 POP_JUMP_IF_TRUE        14

12           6 LOAD_FAST                0 (x)
             9 LOAD_CONST               1 (2)
            12 BINARY_ADD          
            13 RETURN_VALUE        
       >>   14 LOAD_CONST               0 (None)

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