这是成语pythonic？ （someBool和“True Result”或“False Result”） [英] Is this idiom pythonic? (someBool and "True Result" or "False Result")

问题描述

$ p
$ b

而不是：

$

b $ b

  if isUp：
 returnUp
 else：
 returnDown
  
 
 
 
或甚至：
  if isUp elseDown
  
代码如下：
 
 $ b b 
  return isUp和Up或Down
  
我可以看到这是相同的结果，但是这是Python中的典型习语吗？如果是，是否有一些性能黑客运行快？ 
解决方案
a和b或c的成语是如果在Python中，在 PEP 308 发布之前，使用规范的方式表达三元运算书面和实施。这个成语失败的b答案是假的本身;要支持一般情况，可以写
  return（a和[b]或[c]）[0] 
  
拼写的另一种方法是
  return（b，c）[not a] 
  
引入bool类型，可以重写为
  return（c，b）[bool（a）] 
  
（如果不清楚，则转换为bool，不知道是bool已经）
 
 
 
今天，如果事情必须是表达式，则应使用条件表达式语法;否则我建议使用if语句。
 
I just came across this idiom in some open-source Python, and I choked on my drink.

Rather than:
if isUp:
    return "Up"
else:
    return "Down"
or even:
return "Up" if isUp else "Down"
the code read:
return isUp and "Up" or "Down"
I can see this is the same result, but is this a typical idiom in Python? If so, is it some performance hack that runs fast? Or is it just a once-off that needs a code review?
解决方案
The "a and b or c" idiom was the canonical way to express the ternary arithmetic if in Python, before PEP 308 was written and implemented. This idiom fails the "b" answer is false itself; to support the general case, you could write
 return (a and [b] or [c])[0]
An alternative way of spelling it was
 return (b,c)[not a]
which, with the introduction of the bool type, could be rewritten as
 return (c,b)[bool(a)]
(in case it isn't clear: the conversion to bool, and the not operator, is necessary if a is not known to be bool already)

Today, the conditional expression syntax should be used if the thing must be an expression; else I recommend to use the if statement.

                        
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