python 定義函數(shù)時(shí)加個(gè)->是個(gè)什么意思，有幾個(gè)用

idi0t

如題, 像這樣 -> 是什么操作符，哪有說(shuō)明
def func(arg) - > string:
    return arg + "what?"

reyleon

你在哪兒看到Python有這樣的寫(xiě)法?

idi0t

回復(fù) 2# reyleon


    別人python3代碼里，搜了一天了，剛提問(wèn)就在官網(wǎng)翻到了，不過(guò)初看不理解做啥的，還有參數(shù)后加個(gè):和類(lèi)型，能解釋下有什么意義和用處嗎？
4.7.7. Function Annotations

Function annotations are completely optional metadata information about the types used by user-defined functions (see PEP 484 for more information).

Annotations are stored in the __annotations__ attribute of the function as a dictionary and have no effect on any other part of the function. Parameter annotations are defined by a colon after the parameter name, followed by an expression evaluating to the value of the annotation. Return annotations are defined by a literal ->, followed by an expression, between the parameter list and the colon denoting the end of the def statement. The following example has a positional argument, a keyword argument, and the return value annotated:
>>>

>>> def f(ham: str, eggs: str = 'eggs') -> str:
...     print("Annotations:", f.__annotations__)
...     print("Arguments:", ham, eggs)
...     return ham + ' and ' + eggs
...
>>> f('spam')
Annotations: {'ham': <class 'str'>, 'return': <class 'str'>, 'eggs': <class 'str'>}
Arguments: spam eggs
'spam and eggs'


   

idi0t

回復(fù) 2# reyleon
看樣子就是蛋疼的注釋?zhuān)瑹o(wú)語(yǔ)....


   

reyleon

漲姿勢(shì)了, Python3威武..

MMMIX

idi0t 發(fā)表于 2016-06-16 15:26
回復(fù) 2# reyleon

能解釋下有什么意義和用處嗎？

就和 C 里面的函數(shù)聲明是類(lèi)似的作用，可以用來(lái)檢查函數(shù)調(diào)用的時(shí)候參數(shù)類(lèi)型是否正確之類(lèi)的。只不過(guò)，在 Python3 這里，這些信息是可選的，而且其他工具，例如調(diào)試器，也能用；至于具體怎么用，就看工具的作者了，沒(méi)有什么一定之規(guī)。