的Python：允許方法沒有特別的限制被稱爲ALA __getattr__

Question

我想寫出具有執行以下操作的能力的Python類：

c = MyClass() 
a = c.A("a name for A") # Calls internally c.create("A", "a name for A") 
b = c.B("a name for B") # Calls internally c.create("B", "a name for B") 

A和B可以是任何東西（當然，他們「再在數據庫中定義的，但我不希望在我的代碼明確定義它們）

它哈克解決方法是做到以下幾點：

class MyClass(): 
    def __init__(self): 
     self.createItem = "" 

    def create(self, itemType, itemName): 
     print "Creating item %s with name %s" % (itemType, itemName) 

    def create_wrapper(self, name): 
     self.create(self.createItem, name) 

    def __getattr__(self, attrName): 
     self.createItem = attrName 
     return self.create_wrapper 

這將工作當U SER要求是這樣的：

a = c.A("nameA") 
b = c.B("nameB") 

然而，它會翻倒在情況下的函數指針存儲，而不叫：

aFunc = c.A 
bFunc = c.B 
aFunc("nameA") # Is actually calling c.create("B", "nameA"), 
       # as c.B was the last __getattr__() call 
bFunc("nameB") 

的任何東西，我在這裏失蹤有什麼建議？

感謝

編輯：我似乎已經只是想出這一個，但菲利普有一個更優雅的解決方案....

我的解決辦法是：

class MyClassCreator(): 
    def __init__(self, origClass, itemType): 
     self.origClass = origClass 
     self.itemType = itemType 

    def create_wrapper(self, name): 
     return self.origClass.create(self.itemType, name) 

class MyClass(): 
    def __init__(self): 
     self.createItem = "" 

    def create(self, itemType, itemName): 
     print "Creating item %s with name %s" % (itemType, itemName) 

    def __getattr__(self, attrName): 
     return MyClassCreator(self, attrName).create_wrapper 

版本我實際上最終使用（因爲我需要比單個參數更復雜）是:(我不知道這是否可以使用lambda函數來完成......）

def __getattr__(self, attrName): 
    def find_entity_wrapper(*args, **kwargs): 
     return self.find_entity(attrName, *args, **kwargs) 

    return find_entity_wrapper 

Answer 1

有無__getattr__返回本地包裝功能：

class MyClass(object): 
    def create(self, itemType, itemName): 
     print "Creating item %s with name %s" % (itemType, itemName) 

    def __getattr__(self, attrName): 
     def create_wrapper(name): 
      self.create(attrName, name) 
     return create_wrapper 

還有其他的方法來創建包裝函數。在這種情況下，最簡單的一種是使用functools.partial：

import functools 

class MyClass(object): 
    def create(self, itemType, itemName, *args, **kwargs): 
     print "Creating item %s with name %s, args %r and kwargs %r" % (itemType, itemName, args, kwargs) 

    def __getattr__(self, attrName): 
     return functools.partial(self.create, attrName) 

c = MyClass() 
bFunc = c.B 
bFunc("nameB", 1, 2, foo=3) 

這將自動傳遞所有剩餘的參數傳遞給被包裝的函數。

Answer 2

你可以得到你想要的東西通過簡化：

class MyClass(): 

    def create(self, itemType, itemName): 
     print "Creating item %s with name %s" % (itemType, itemName) 

    def __getattr__(self, attrName): 
     return lambda x: self.create(attrName, x) 

c = MyClass() 
a = c.A("nameA") 
b = c.B("nameB") 


af = c.A 
bf = c.B 
af("nameA") 
bf("nameB") 

打印：

Creating item A with name nameA 
Creating item B with name nameB 
Creating item A with name nameA 
Creating item B with name nameB