Question

TL; DR：必须为每个属性定义一组唯一的getter和setter（）＆＃39; d变量很糟糕。我可以定义通用的getter和setter，并将它们用于我想要的任何变量吗？

我们说我和一些不错的吸气者和制定者一起上课：

class Foo
    def getter(self):
        return _bar+' sasquatch'

    def setter(self, value):
        _bar = value+' unicorns'

    bar = property(getter, setter)

非常好，对吧？

现在让我说我输入另一个名为＆＃34; baz＆＃34;而且我不希望它被这个sasquatch / unicorn乐趣所遗忘。好吧，我想我可以制作另一组getter和setter：

class Foo
    def bar_getter(self):
        return _bar+' sasquatch'

    def bar_setter(self, value):
        _bar = value+' unicorns'

    bar = property(bar_getter, bar_setter)

    def baz_getter(self):
        return _baz+' sasquatch'

    def baz_setter(self, value):
        _baz = value+' unicorns'

    baz = property(baz_getter, baz_setter)

但那不是很干，而且不必要地弄乱了我的代码。我想我可以做一点DRYer：

class Foo
    def unicornify(self, value):
        return value+' unicorns'

    def sasquatchify(self, value):
        return value+' sasquatch'

    def bar_getter(self):
        return self.sasquatchify(_bar)

    def bar_setter(self, value):
        _bar = self.unicornify(_bar)

    bar = property(bar_getter, bar_setter)

    def baz_getter(self):
        return self.sasquatchify(_baz)

    def baz_setter(self, value):
        _baz = self.unicornify(_baz)

    baz = property(baz_getter, baz_setter)

虽然这可能会使我的代码DRYer，但它并不理想。如果我想unicornify和sasquatchify两个更多的变量，我将不得不再添加四个函数！

必须有更好的方法来做到这一点。我可以在多个变量中使用单个通用getter和/或setter吗？

Unicorn-less和sasquatch-less实际实现：我使用SQLAlchemy ORM，并希望在从数据库存储和检索数据时转换一些数据。一些转换适用于多个变量，我不想让我的类与getter和setter混乱。

Answer 1

如何：

def sasquatchicorn(name):
    return property(lambda self: getattr(self, name) + ' sasquatch',
                    lambda self, val: setattr(self, name, val + ' unicorns'))

class Foo(object):
    bar = sasquatchicorn('_bar')
    baz = sasquatchicorn('_baz')

更一般地说：

def sasquatchify(val):
    return val + ' sasquatch'

def unicornify(val):
    return val + ' unicorns'

def getset(name, getting, setting):
    return property(lambda self: getting(getattr(self, name)),
                    lambda self, val: setattr(self, name, setting(val)))

class Foo(object):
    bar = getset('_bar', sasquatchify, unicornify)
    baz = getset('_baz', sasquatchify, unicornify)

或者，只需要更多的工作，就可以使用完整的描述符协议，如agf's answer中所述。

Answer 2

这是descriptor protocol property所基于的内容：

class Sasicorn(object):                              
    def __init__(self, attr):                        
        self.attr = "_" + attr                       
    def __get__(self, obj, objtype):                 
        return getattr(obj, self.attr) + ' sasquatch'
    def __set__(self, obj, value):                   
        setattr(obj, self.attr, value + ' unicorns') 

class Foo(object):                                   
    def __init__(self, value = "bar"):               
        self.bar = value                             
        self.baz = "baz"                             
    bar = Sasicorn('bar')                            
    baz = Sasicorn('baz')                            

foo = Foo()                                          
foo2 = Foo('other')                                  
print foo.bar                                        
# prints bar unicorns sasquatch
print foo.baz                                        
# prints baz unicorns sasquatch
print foo2.bar                                       
# prints other unicorns sasquatch

虽然工厂功能中的property可能适用于您的玩具示例，但听起来您可能需要更多控制您的实际用例。

Answer 3

我的一位同事建议使用闭包来返回getter和setter函数，这是我决定使用的。

class Foo(object):
    def setter(var):
        def set(self, value):
            setattr(self, var, value+' unicorn')
        return set

    def getter(var):
        def get(self):
            return getattr(self, var)+' sasquatch'
        return get

    bar = property(getter('_bar'), setter('_bar'))

f = Foo()
f.foo = 'hi'
print f.foo

但是，谢谢大家的答案：）

Answer 4

使用getattribute和setattr，您可以为过去和将来的所有属性定义此内容。

class Foo(object):                                                                                                                           

  x = 3 

  def __getattribute__(self, attr):
    return str(object.__getattribute__(self, attr)) + ' sasquatch'

  def __setattr__(self, attr, value):
    object.__setattr__(self, attr, str(value) + ' unicorn')

print Foo.x
f = Foo()
print f.x 
f.y = 4 
print f.y

打印：

3
3 sasquatch
4 unicorn sasquatch

Answer 5

# coding=utf-8
__author__ = 'Ahmed Şeref GÜNEYSU'


class Student(object):
    def __init__(self, **kwargs):
        for k, v in kwargs.iteritems():
            self.__setattr__(k, v)

if __name__ == '__main__':
    o = Student(first_name='Ahmed Şeref', last_name='GÜNEYSU')
    print "{0} {1}".format(o.first_name, o.last_name)
    print o.email

给予

Ahmed Şeref GÜNEYSU
  File "/Users/ahmed/PycharmProjects/sanbox/abstract_classes/object_initializer/__init__.py", line 13, in <module>
    print o.email
AttributeError: 'Student' object has no attribute 'email'

Process finished with exit code 137

Python：通用的getter和setter

5 个答案: