Python 是否可以使用 if 语句编写单行 return 语句？
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Is it possible to write single line return statement with if statement?
提问by user462455
Is is possible to return from a method in single line in python
是否可以从python中的单行方法返回
Looking for something like this
寻找这样的东西
return None if x is None
Tried above, and it is invalid syntax
上面试过了，语法无效
I could easily do:
我可以轻松做到：
if x is None:
return None
But just curious if I can combine above if statement into a single line
但只是好奇我是否可以将上面的 if 语句组合成一行
采纳答案by nakedfanatic
It is possible to write a standard "if" statement on a single line:
可以在一行中编写标准的“if”语句：
if x is None: return None
However the pep 8 style guiderecommends against doing this:
然而，pep 8 风格指南建议不要这样做：
Compound statements (multiple statements on the same line) are generally discouraged
通常不鼓励复合语句（同一行上的多个语句）
回答by TerryA
Yes, it's called a conditional expression:
是的，它被称为条件表达式：
return None if x is None else something_else
You need an else somethingin a conditional for it to work.
您需要一个else somethingin 条件才能使其工作。
回答by smac89
You could also try the list[bool]expression:
你也可以试试这个list[bool]表达式：
return [value, None][x == None]
Now if the second bracket evaluates to true, None is returned otherwise, the value you want to return is returned
现在，如果第二个括号评估为真，则返回 None 否则，将返回您要返回的值
回答by Steve Jessop
Disclaimer: don't actually do this. If you really want a one-liner then like nakedfanatic says just break the rule of thumb from PEP-8. However, it illustrates why returnisn't behaving as you thought it might, and what a thing would look like that does behave as you thought returnmight.
免责声明：实际上不要这样做。如果你真的想要一个单线，那么就像nakedfanatic所说的那样，打破PEP-8的经验法则。然而，它说明了为什么return行为不像你想象的那样，以及一个事物看起来像你想象的return那样。
The reason you can't say return None if x is None, is that returnintroduces a statement, not an expression. So there's no way to parenthesise it (return None) if x is None else (pass), or whatever.
你不能说的原因return None if x is None是它return引入了一个语句，而不是一个表达式。所以没有办法把它括起来(return None) if x is None else (pass)，或者其他什么。
That's OK, we can fix that. Let's write a function retthat behaves like returnexcept that it's an expression rather than a full statement:
没关系，我们可以解决这个问题。让我们编写一个函数ret，return它的行为类似于一个表达式而不是一个完整的语句：
class ReturnValue(Exception):
def __init__(self, value):
Exception.__init__(self)
self.value = value
def enable_ret(func):
def decorated_func(*args, **kwargs):
try:
return func(*args, **kwargs)
except ReturnValue as exc:
return exc.value
return decorated_func
def ret(value):
raise ReturnValue(value)
@enable_ret
def testfunc(x):
ret(None) if x is None else 0
# in a real use-case there would be more code here
# ...
return 1
print testfunc(None)
print testfunc(1)
