python函數(shù)原型定義那行有個(gè)箭頭是什么語(yǔ)法？比如

這是函數(shù)注解,Python 3.x引入,它的特點(diǎn)有

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對(duì)函數(shù)的參數(shù)進(jìn)行類型注解,以冒號(hào)標(biāo)記

對(duì)函數(shù)的返回值進(jìn)行類型注解,以箭頭標(biāo)記

只對(duì)函數(shù)參數(shù)或返回值做一個(gè)輔助的說(shuō)明，并不對(duì)函數(shù)參數(shù)或返回值進(jìn)行類型檢查

提供給第三方工具，做代碼分析，發(fā)現(xiàn)隱藏bug

函數(shù)注解的信息，保存在__annotations__屬性中

注解本身是一個(gè)字典類型的數(shù)據(jù)

你的程序我?guī)湍阃晟屏?函數(shù)注解部分的解釋見注釋),你看看吧

from?typing?import?List

def?f(a)?-?List[dict]:?#函數(shù)注解,返回一個(gè)字典列表,但是它不對(duì)返回值類型進(jìn)行檢查

print(a)??#打印字典

return?[a]?#返回字典列表

print(f.__annotations__)?#打印函數(shù)注解

l={'Name':?'Zara','Age':17}?#把字典傳入函數(shù)

print(f(l))?#打印函數(shù)返回值

源代碼(注意源代碼的縮進(jìn))

python3函數(shù)定義的格式問(wèn)題

-:標(biāo)記返回函數(shù)注釋,信息作為.__annotations__屬性提供,__annotations__屬性是字典。鍵return是用于在箭頭后檢索值的鍵。但是在Python中3.5，PEP 484 - Type Hints附加了一個(gè)含義：-用于指示函數(shù)返回的類型。它似乎也將在未來(lái)版本中強(qiáng)制執(zhí)行。

eg:

def test() - [1, 2, 3, 4, 5]:

pass

print(test.__annotations__)

輸出：

{'return': [1, 2, 3, 4, 5]}

python畫箭頭(用內(nèi)置的函數(shù))怎么畫？

你用的graphics模塊？這不是內(nèi)置的，雖然它是調(diào)用內(nèi)置的Tkinter畫圖。

option可以是"first","last","both"或"none"。見graphics.py:

def setArrow(self, option):

if not option in ["first","last","both","none"]:

raise GraphicsError(BAD_OPTION)

self._reconfig("arrow", option)

細(xì)節(jié)要查Tk文檔：

6.6. The canvas line object

In general, a line can consist of any number of segments connected end to end, and each segment can be straight or curved. To create a canvas line object on a canvas C, use:

id = C.create_line ( x0, y0, x1, y1, ..., xn, yn, option, ... )

The line goes through the series of points

(x0,

y0),

(x1,

y1),

…

(xn,

yn).

Options include:

arrow The default is for the line to have no arrowheads. Use

arrow=FIRST to get an arrowhead at the(x0,y0)end of the line. Use

arrow=LAST to get an arrowhead at the far end. Use

arrow=BOTH for arrowheads at both ends.