python開發_function annotations

在看python的API的時候，發現了一個有趣的東東，即：python的方法(函數)注解(Function Annotation)

原文：

4.7.7. Function Annotations

Function annotations are completely optional, arbitrary metadata information about user-defined functions. Neither Python itself nor the standard library use function annotations in any way; this section just shows the syntax. Third-party projects are free to use function annotations for documentation, type checking, and other uses.

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 with nonsense:
>>> def f(ham: 42, eggs: int = 'spam') -> "Nothing to see here":
...     print("Annotations:", f.__annotations__)
...     print("Arguments:", ham, eggs)
...
>>> f('wonderful')
Annotations: {'eggs': <class 'int'>, 'return': 'Nothing to see here', 'ham': 42}
Arguments: wonderful spam

初略的看了一下，沒有理解其參數的涵義，就照着寫了一遍程序：

def f(ham: 42, eggs: int = 'spam') -> 'Nothing to see here':
    print('Annotations:', f.__annotations__)
    print('Arguments:', ham, eggs)

f('wonderful')

運行效果：

Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
Annotations: {'eggs': <class 'int'>, 'ham': 42, 'return': 'Nothing to see here'}
Arguments: wonderful spam
>>> 

運行效果和python的API中描述的一樣。

搜索了一些資料發現了參數的涵義：

我們先來看看幾個demo：

ONE : 這里給ham賦一個初始值'Hongten'

#這里給ham賦一個初始值'Hongten'
def f(ham: 42 = 'Hongten', eggs: int = 'spam') -> 'Nothing to see here':
    print('Annotations:', f.__annotations__)
    print('Arguments:', ham, eggs)

f()

運行效果：

Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
Annotations: {'eggs': <class 'int'>, 'ham': 42, 'return': 'Nothing to see here'}
Arguments: Hongten spam
>>> 

//TWO :  這里把42變為：'這里是ham的注釋'

#這里把42變為：'這里是ham的注釋'
def f(ham: '這里是ham的注釋' = 'Hongten', eggs: int = 'spam') -> 'Nothing to see here':
    print('Annotations:', f.__annotations__)
    print('Arguments:', ham, eggs)

f()

運行效果：

Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
Annotations: {'eggs': <class 'int'>, 'return': 'Nothing to see here', 'ham': '這里是ham的注釋'}
Arguments: Hongten spam
>>> 

//THREE :  這里把int變為str

#這里把int變為str
def f(ham: '這里是ham的注釋' = 'Hongten', eggs: str = 'spam') -> 'Nothing to see here':
    print('Annotations:', f.__annotations__)
    print('Arguments:', ham, eggs)

f()

運行效果：

Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
Annotations: {'eggs': <class 'str'>, 'ham': '這里是ham的注釋', 'return': 'Nothing to see here'}
Arguments: Hongten spam
>>> 

//FOUR :  看看一段java函數代碼

  /**
     * 判斷一個字符串是否全為字母,此方法比上面的isAllChar方法效率要高，但是需要的是str中包含非字母字符在靠前面
     * 如："a2bcd",對於這個字符串，到字符"2"的時候就會終止判斷
     * 
     * @param str
     *            所需判斷的字符串
     * @return str中是否全為字母字符
     */
    public static boolean isAllChars(String str) {
        if (str == null || str.equals("")) {
            return false;
        }
        boolean flag = true;
        for (int i = 0; i < str.length(); i++) {
            if ((str.charAt(i) < 'a' || str.charAt(i) > 'z')
                    && (str.charAt(i) < 'A' || str.charAt(i) > 'Z')) {
                flag = false;
                break;
            }
        }
        return flag;
    }

到這里你大概知道我想說什么了吧！

總結：

def f(ham: 42, eggs: int = 'spam') -> "Nothing to see here":
    print("Annotations:", f.__annotations__)
    print("Arguments:", ham, eggs)

#def關鍵字定義了函數f，在函數f中有兩個參數：ham，eggs。
#其中ham沒有默認值，而eggs是由默認值的，其默認值為'spam'.
#參數ham的注釋部分為：42；參數eggs的注釋部分為：int
# "Nothing to see here"是返回值的注釋，這個必須用 '->'連接

#看了java代碼后，你會有更直觀的認識，注釋嘛，你可以根據你自己的想法，想怎么寫就怎么寫，如42，int；不過不好的注釋有時候會給別人閱讀代碼帶來很大的麻煩

#如果上面的代碼是這樣寫：
def f(ham: int = 42, eggs: str = 'spam') -> 'Nothing to see here':
    print("Annotations:", f.__annotations__)
    print("Arguments:", ham, eggs)

#我想很多人閱讀代碼的時候就很容易理解啦 
#上面只是個人觀點，如果不正確的地方，還請大家指正 #同時也希望大家相互學習：[e-mail]