Python 如何向类动态添加属性？
目标是创建一个行为类似于db resultset的模拟类 例如，如果数据库查询使用dict表达式返回，Python 如何向类动态添加属性？,python,properties,runtime,monkeypatching,Python,Properties,Runtime,Monkeypatching,目标是创建一个行为类似于db resultset的模拟类 例如，如果数据库查询使用dict表达式返回，{'ab'：100，'cd'：200}，那么我希望看到： >>> dummy.ab 100 起初我想也许我可以这样做： ks = ['ab', 'cd'] vs = [12, 34] class C(dict): def __init__(self, ks, vs): for i, k in enumerate(ks): sel
{'ab'：100，'cd'：200}>>> dummy.ab
100
ks = ['ab', 'cd']
vs = [12, 34]
class C(dict):
def __init__(self, ks, vs):
for i, k in enumerate(ks):
self[k] = vs[i]
setattr(self, k, property(lambda x: vs[i], self.fn_readyonly))
def fn_readonly(self, v)
raise "It is ready only"
if __name__ == "__main__":
c = C(ks, vs)
print c.ab
c.absetattrk=property（lambda x:vs[i]）另外，我知道在中有一个备选方案，我不确定我是否完全理解这个问题，但您可以在运行时使用类的内置
\uu dict\uuuclass C(object):
def __init__(self, ks, vs):
self.__dict__ = dict(zip(ks, vs))
if __name__ == "__main__":
ks = ['ab', 'cd']
vs = [12, 34]
c = C(ks, vs)
print(c.ab) # 12
def getx(self):
return self._x
def setx(self, value):
self._x = value
def delx(self):
del self._x
无法在运行时向实例添加新的
property（）\uuu getattribute\uuufrom collections import namedtuple
Foo = namedtuple('Foo', ['bar', 'quux'])
foo = Foo(bar=13, quux=74)
print foo.bar, foo.quux
foo2 = Foo() # error
如果您确实需要编写自己的setter，则必须在类级别进行元编程<代码>属性（）对实例无效。动态附加属性的唯一方法是使用新属性创建新类及其实例
class Holder: p = property(lambda x: vs[i], self.fn_readonly)
setattr(self, k, Holder().p)
您不需要为此使用属性。只需重写
\uuuuu setattr\uuuuuclass C(object):
def __init__(self, keys, values):
for (key, value) in zip(keys, values):
self.__dict__[key] = value
def __setattr__(self, name, value):
raise Exception("It is read only!")
实现这一目标的最佳方法是定义
\uuuuu插槽ks = ['ab', 'cd']
vs = [12, 34]
class C(dict):
__slots__ = []
def __init__(self, ks, vs): self.update(zip(ks, vs))
def __getattr__(self, key): return self[key]
if __name__ == "__main__":
c = C(ks, vs)
print c.ab
12 c.ab = 33
AttributeError:'C'对象没有属性'ab'class atdict(dict):
__getattr__= dict.__getitem__
__setattr__= dict.__setitem__
__delattr__= dict.__delitem__
class data(dict,object):
def __init__(self,*args,**argd):
dict.__init__(self,*args,**argd)
def __getattr__(self,name):
return self[name]
def __setattr__(self,name,value):
raise AttributeError,"Attribute '%s' of '%s' object cannot be set"%(name,self.__class__.__name__)
def __delattr__(self,name):
raise AttributeError,"Attribute '%s' of '%s' object cannot be deleted"%(name,self.__class__.__name__)
我问了一个类似的问题来创建一个创建简单类型的类工厂。结果是有了一个工作版本的类工厂。 以下是答案的一小部分：
def Struct(*args, **kwargs):
def init(self, *iargs, **ikwargs):
for k,v in kwargs.items():
setattr(self, k, v)
for i in range(len(iargs)):
setattr(self, args[i], iargs[i])
for k,v in ikwargs.items():
setattr(self, k, v)
name = kwargs.pop("name", "MyStruct")
kwargs.update(dict((k, None) for k in args))
return type(name, (object,), {'__init__': init, '__slots__': kwargs.keys()})
>>> Person = Struct('fname', 'age')
>>> person1 = Person('Kevin', 25)
>>> person2 = Person(age=42, fname='Terry')
>>> person1.age += 10
>>> person2.age -= 10
>>> person1.fname, person1.age, person2.fname, person2.age
('Kevin', 35, 'Terry', 32)
>>>
你可以使用它的一些变体来创建默认值，这是你的目标（这个问题中也有一个解决这个问题的答案）。我想我应该扩展这个答案，因为我已经长大了，更聪明了，知道发生了什么。迟做总比不做好 可以将属性动态添加到类中。但这就是问题所在：您必须将其添加到类中
属性实际上是一个称为。它是一个在给定类上为给定属性提供自定义处理的对象。有点像从\uuu getattribute\uuu
中提取一个巨大if
树的一种方法
在上面的示例中，当我询问foo.b
时，Python看到类上定义的b
实现了描述符协议，这意味着它是一个具有\uuuuu get\uuuuu
、\uu set\uuuuuu
或\uu delete\uuu
方法的对象。描述符声明负责处理该属性，因此Python调用Foo.b.\uuu get\uuu（Foo，Foo）
，返回值作为属性值传递给您。在属性
的情况下，这些方法中的每一个都只调用传递给属性
构造函数的fget
、fset
或fdel
描述符实际上是Python公开其整个OO实现管道的方式。事实上，还有一种描述符比属性
更常见
>>> class Foo(object):
... def bar(self):
... pass
...
>>> Foo().bar
<bound method Foo.bar of <__main__.Foo object at 0x7f2a439d5dd0>>
>>> Foo().bar.__get__
<method-wrapper '__get__' of instancemethod object at 0x7f2a43a8a5a0>
无论如何，我怀疑这就是描述符只对类起作用的原因：它们是一种形式化的东西，从一开始就为类提供了动力。它们甚至是规则的例外：显然，您可以将描述符分配给类，而类本身就是类型的实例
！事实上，试图读取Foo.bar
仍然会调用属性；当作为类属性访问时，描述符返回它们自己是惯用的
ks = ['ab', 'cd']
vs = [12, 34]
class C(dict):
__slots__ = []
def __init__(self, ks, vs): self.update(zip(ks, vs))
def __getattr__(self, key): return self[key]
if __name__ == "__main__":
c = C(ks, vs)
print c.ab
我认为，几乎所有Python的OO系统都可以用Python表示，这是非常酷的。：）
哦，如果你感兴趣的话，我不久前写了一篇文章。我最近遇到了一个类似的问题，我提出的解决方案使用了\uuu getattr\uuuu
和\uu setattr\uuuuu
来处理我想要它处理的属性，其他的一切都会传递给原始属性
class C(object):
def __init__(self, properties):
self.existing = "Still Here"
self.properties = properties
def __getattr__(self, name):
if "properties" in self.__dict__ and name in self.properties:
return self.properties[name] # Or call a function, etc
return self.__dict__[name]
def __setattr__(self, name, value):
if "properties" in self.__dict__ and name in self.properties:
self.properties[name] = value
else:
self.__dict__[name] = value
if __name__ == "__main__":
my_properties = {'a':1, 'b':2, 'c':3}
c = C(my_properties)
assert c.a == 1
assert c.existing == "Still Here"
c.b = 10
assert c.properties['b'] == 10
这只是如何达到预期效果的另一个例子
class Foo(object):
_bar = None
@property
def bar(self):
return self._bar
@bar.setter
def bar(self, value):
self._bar = value
def __init__(self, dyn_property_name):
setattr(Foo, dyn_property_name, Foo.bar)
现在我们可以做一些事情，比如：
>>> foo = Foo('baz')
>>> foo.baz = 5
>>> foo.bar
5
>>> foo.baz
5
如何向python类动态添加属性？
假设您有一个要添加属性的对象。通常，当我需要开始管理对代码中具有下游用法的属性的访问时，我希望使用属性，以便维护一致的API。现在，我通常会将它们添加到定义对象的源代码中，但假设您没有该访问权限，或者您需要真正以编程方式动态选择函数
#!/usr/bin/python3
class Counter:
def __init__(self):
cls = self.__class__
self._count = 0
cls.count = self.count_ref()
def count_get(self):
print(f'count_get: {self._count}')
return self._count
def count_set(self, value):
self._count = value
print(f'count_set: {self._count}')
def count_del(self):
print(f'count_del: {self._count}')
def count_ref(self):
cls = self.__class__
return property(fget=cls.count_get, fset=cls.count_set, fdel=cls.count_del)
counter = Counter()
counter.count
for i in range(5):
counter.count = i
del counter.count
'''
output
======
count_get: 0
count_set: 0
count_set: 1
count_set: 2
count_set: 3
count_set: 4
count_del: 4
'''
创建一个类
使用基于的示例，让我们创建一个具有“隐藏”属性的对象类，并创建其实例：
class C(object):
'''basic class'''
_x = None
o = C()
在Python中，我们希望有一种明显的瘦方法
class C(object):
'''basic class'''
_x = None
o = C()
def getx(self):
return self._x
def setx(self, value):
self._x = value
def delx(self):
del self._x
C.x = property(getx, setx, delx, "I'm the 'x' property.")
>>> o.x = 'foo'
>>> o.x
'foo'
>>> del o.x
>>> print(o.x)
None
>>> help(C.x)
Help on property:
I'm the 'x' property.
@property
def x(self):
'''I'm the 'x' property.'''
return self._x
@x.setter
def x(self, value):
self._x = value
@x.deleter
def x(self):
del self._x
C.x = x
>>> help(C.x)
Help on property:
I'm the 'x' property.
>>> o.x
>>> o.x = 'foo'
>>> o.x
'foo'
>>> del o.x
>>> print(o.x)
None
>>> dummy.ab
100
import collections
data = {'ab':100, 'cd':200}
def maketuple(d):
'''given a dict, return a namedtuple'''
Tup = collections.namedtuple('TupName', d.keys()) # iterkeys in Python2
return Tup(**d)
dummy = maketuple(data)
dummy.ab
class Foo:
def __init__(self):
# we can dynamically have access to the properties dict using __dict__
self.__dict__['foo'] = 'bar'
assert Foo().foo == 'bar'
# or we can use __getattr__ and __setattr__ to execute code on set/get
class Bar:
def __init__(self):
self._data = {}
def __getattr__(self, key):
return self._data[key]
def __setattr__(self, key, value):
self._data[key] = value
bar = Bar()
bar.foo = 'bar'
assert bar.foo == 'bar'
class atdict(dict):
def __init__(self, value, **kwargs):
super().__init__(**kwargs)
self.__dict = value
def __getattr__(self, name):
for key in self.__dict:
if type(self.__dict[key]) is list:
for idx, item in enumerate(self.__dict[key]):
if type(item) is dict:
self.__dict[key][idx] = atdict(item)
if type(self.__dict[key]) is dict:
self.__dict[key] = atdict(self.__dict[key])
return self.__dict[name]
d1 = atdict({'a' : {'b': [{'c': 1}, 2]}})
print(d1.a.b[0].c)
>> 1
class ExampleClass():
def __init__(self, argv):
for key, val in argv.items():
self.__dict__[key] = val
if __name__ == '__main__':
argv = {'intro': 'Hello World!'}
instance = ExampleClass(argv)
print instance.intro
_instance.SetAccessors( _key, _value [ , _key, _value ] .. ) Instance Class Helper Function: Allows assigning many keys / values on a single line - useful for initial setup, or to minimize lines. In short: Calls this.Set<Name>( _value ) for each _key / _value pairing.
_instance.ResetAccessors( _key [ , _key ] .. ) Instance Class Helper Function: Allows resetting many key stored values to None on a single line. In short: Calls this.Reset<Name>() for each name provided.
Note: Functions below may list self.Get / Set / Name( _args ) - self is meant as the class instance reference in the cases below - coded as this in AccessorFuncBase Class.
this.GetX( _default_override = None, _ignore_defaults = False ) GET: Returns IF ISSET: STORED_VALUE .. IF IGNORE_DEFAULTS: None .. IF PROVIDED: DEFAULT_OVERRIDE ELSE: DEFAULT_VALUE 100
this.GetXRaw( ) RAW: Returns STORED_VALUE 100
this.IsXSet( ) ISSET: Returns ( STORED_VALUE != None ) True
this.GetXToString( ) GETSTR: Returns str( GET ) 100
this.GetXLen( _default_override = None, _ignore_defaults = False ) LEN: Returns len( GET ) 3
this.GetXLenToString( _default_override = None, _ignore_defaults = False ) LENSTR: Returns str( len( GET ) ) 3
this.GetXDefaultValue( ) DEFAULT: Returns DEFAULT_VALUE 1111
this.GetXAccessor( ) ACCESSOR: Returns ACCESSOR_REF ( self.__<key> ) [ AccessorFuncBase ] Key: x : Class ID: 2231452344344 : self ID: 2231448283848 Default: 1111 Allowed Types: {"<class 'int'>": "<class 'type'>", "<class 'float'>": "<class 'type'>"} Allowed Values: None
this.GetXAllowedTypes( ) ALLOWED_TYPES: Returns Allowed Data-Types {"<class 'int'>": "<class 'type'>", "<class 'float'>": "<class 'type'>"}
this.GetXAllowedValues( ) ALLOWED_VALUES: Returns Allowed Values None
this.GetXHelpers( ) HELPERS: Returns Helper Functions String List - ie what you're reading now... THESE ROWS OF TEXT
this.GetXKeyOutput( ) Returns information about this Name / Key ROWS OF TEXT
this.GetXGetterOutput( ) Returns information about this Name / Key ROWS OF TEXT
this.SetX( _value ) SET: STORED_VALUE Setter - ie Redirect to __<Key>.Set N / A
this.ResetX( ) RESET: Resets STORED_VALUE to None N / A
this.HasXGetterPrefix( ) Returns Whether or Not this key has a Getter Prefix... True
this.GetXGetterPrefix( ) Returns Getter Prefix... Get
this.GetXName( ) Returns Accessor Name - Typically Formal / Title-Case X
this.GetXKey( ) Returns Accessor Property Key - Typically Lower-Case x
this.GetXAccessorKey( ) Returns Accessor Key - This is to access internal functions, and static data... __x
this.GetXDataKey( ) Returns Accessor Data-Storage Key - This is the location where the class instance value is stored.. _x
_foo --- MyClass: ---- id( this.__class__ ): 2231452349064 :::: id( this ): 2231448475016
Key Getter Value | Raw Key Raw / Stored Value | Get Default Value Default Value | Get Allowed Types Allowed Types | Get Allowed Values Allowed Values |
Name: _foo | _Name: _foo | __Name.DefaultValue( ): AccessorFuncDemoClass | __Name.GetAllowedTypes( ) <class 'str'> | __Name.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
x: 1111 | _x: None | __x.DefaultValue( ): 1111 | __x.GetAllowedTypes( ) (<class 'int'>, <class 'float'>) | __x.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
y: 2222 | _y: None | __y.DefaultValue( ): 2222 | __y.GetAllowedTypes( ) (<class 'int'>, <class 'float'>) | __y.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
z: 3333 | _z: None | __z.DefaultValue( ): 3333 | __z.GetAllowedTypes( ) (<class 'int'>, <class 'float'>) | __z.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
Blah: <class 'int'> | _Blah: None | __Blah.DefaultValue( ): <class 'int'> | __Blah.GetAllowedTypes( ) <class 'str'> | __Blah.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
Width: 1 | _Width: None | __Width.DefaultValue( ): 1 | __Width.GetAllowedTypes( ) (<class 'int'>, <class 'bool'>) | __Width.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
Height: 0 | _Height: None | __Height.DefaultValue( ): 0 | __Height.GetAllowedTypes( ) <class 'int'> | __Height.GetAllowedValues( ) (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) |
Depth: 2 | _Depth: None | __Depth.DefaultValue( ): 2 | __Depth.GetAllowedTypes( ) Saved Value Restricted to Authorized Values ONLY | __Depth.GetAllowedValues( ) (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) |
this.IsNameSet( ): True this.GetName( ): _foo this.GetNameRaw( ): _foo this.GetNameDefaultValue( ): AccessorFuncDemoClass this.GetNameLen( ): 4 this.HasNameGetterPrefix( ): <class 'str'> this.GetNameGetterPrefix( ): None
this.IsXSet( ): False this.GetX( ): 1111 this.GetXRaw( ): None this.GetXDefaultValue( ): 1111 this.GetXLen( ): 4 this.HasXGetterPrefix( ): (<class 'int'>, <class 'float'>) this.GetXGetterPrefix( ): None
this.IsYSet( ): False this.GetY( ): 2222 this.GetYRaw( ): None this.GetYDefaultValue( ): 2222 this.GetYLen( ): 4 this.HasYGetterPrefix( ): (<class 'int'>, <class 'float'>) this.GetYGetterPrefix( ): None
this.IsZSet( ): False this.GetZ( ): 3333 this.GetZRaw( ): None this.GetZDefaultValue( ): 3333 this.GetZLen( ): 4 this.HasZGetterPrefix( ): (<class 'int'>, <class 'float'>) this.GetZGetterPrefix( ): None
this.IsBlahSet( ): False this.GetBlah( ): <class 'int'> this.GetBlahRaw( ): None this.GetBlahDefaultValue( ): <class 'int'> this.GetBlahLen( ): 13 this.HasBlahGetterPrefix( ): <class 'str'> this.GetBlahGetterPrefix( ): None
this.IsWidthSet( ): False this.GetWidth( ): 1 this.GetWidthRaw( ): None this.GetWidthDefaultValue( ): 1 this.GetWidthLen( ): 1 this.HasWidthGetterPrefix( ): (<class 'int'>, <class 'bool'>) this.GetWidthGetterPrefix( ): None
this.IsDepthSet( ): False this.GetDepth( ): 2 this.GetDepthRaw( ): None this.GetDepthDefaultValue( ): 2 this.GetDepthLen( ): 1 this.HasDepthGetterPrefix( ): None this.GetDepthGetterPrefix( ): (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
this.IsHeightSet( ): False this.GetHeight( ): 0 this.GetHeightRaw( ): None this.GetHeightDefaultValue( ): 0 this.GetHeightLen( ): 1 this.HasHeightGetterPrefix( ): <class 'int'> this.GetHeightGetterPrefix( ): (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
this.IsNameSet( ): True this.GetName( ): _foo this.GetNameRaw( ): _foo this.GetNameDefaultValue( ): AccessorFuncDemoClass this.GetNameLen( ): 4 this.HasNameGetterPrefix( ): <class 'str'> this.GetNameGetterPrefix( ): None
this.IsXSet( ): True this.GetX( ): 10 this.GetXRaw( ): 10 this.GetXDefaultValue( ): 1111 this.GetXLen( ): 2 this.HasXGetterPrefix( ): (<class 'int'>, <class 'float'>) this.GetXGetterPrefix( ): None
this.IsYSet( ): True this.GetY( ): 10 this.GetYRaw( ): 10 this.GetYDefaultValue( ): 2222 this.GetYLen( ): 2 this.HasYGetterPrefix( ): (<class 'int'>, <class 'float'>) this.GetYGetterPrefix( ): None
this.IsZSet( ): True this.GetZ( ): 10 this.GetZRaw( ): 10 this.GetZDefaultValue( ): 3333 this.GetZLen( ): 2 this.HasZGetterPrefix( ): (<class 'int'>, <class 'float'>) this.GetZGetterPrefix( ): None
this.IsBlahSet( ): True this.GetBlah( ): string Blah this.GetBlahRaw( ): string Blah this.GetBlahDefaultValue( ): <class 'int'> this.GetBlahLen( ): 11 this.HasBlahGetterPrefix( ): <class 'str'> this.GetBlahGetterPrefix( ): None
this.IsWidthSet( ): True this.GetWidth( ): False this.GetWidthRaw( ): False this.GetWidthDefaultValue( ): 1 this.GetWidthLen( ): 5 this.HasWidthGetterPrefix( ): (<class 'int'>, <class 'bool'>) this.GetWidthGetterPrefix( ): None
this.IsDepthSet( ): True this.GetDepth( ): 9 this.GetDepthRaw( ): 9 this.GetDepthDefaultValue( ): 2 this.GetDepthLen( ): 1 this.HasDepthGetterPrefix( ): None this.GetDepthGetterPrefix( ): (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
this.IsHeightSet( ): True this.GetHeight( ): 9 this.GetHeightRaw( ): 9 this.GetHeightDefaultValue( ): 0 this.GetHeightLen( ): 1 this.HasHeightGetterPrefix( ): <class 'int'> this.GetHeightGetterPrefix( ): (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
_foo --- MyClass: ---- id( this.__class__ ): 2231452349064 :::: id( this ): 2231448475016
Key Getter Value | Raw Key Raw / Stored Value | Get Default Value Default Value | Get Allowed Types Allowed Types | Get Allowed Values Allowed Values |
Name: _foo | _Name: _foo | __Name.DefaultValue( ): AccessorFuncDemoClass | __Name.GetAllowedTypes( ) <class 'str'> | __Name.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
x: 10 | _x: 10 | __x.DefaultValue( ): 1111 | __x.GetAllowedTypes( ) (<class 'int'>, <class 'float'>) | __x.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
y: 10 | _y: 10 | __y.DefaultValue( ): 2222 | __y.GetAllowedTypes( ) (<class 'int'>, <class 'float'>) | __y.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
z: 10 | _z: 10 | __z.DefaultValue( ): 3333 | __z.GetAllowedTypes( ) (<class 'int'>, <class 'float'>) | __z.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
Blah: string Blah | _Blah: string Blah | __Blah.DefaultValue( ): <class 'int'> | __Blah.GetAllowedTypes( ) <class 'str'> | __Blah.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
Width: False | _Width: False | __Width.DefaultValue( ): 1 | __Width.GetAllowedTypes( ) (<class 'int'>, <class 'bool'>) | __Width.GetAllowedValues( ) Saved Value Restrictions Levied by Data-Type |
Height: 9 | _Height: 9 | __Height.DefaultValue( ): 0 | __Height.GetAllowedTypes( ) <class 'int'> | __Height.GetAllowedValues( ) (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) |
Depth: 9 | _Depth: 9 | __Depth.DefaultValue( ): 2 | __Depth.GetAllowedTypes( ) Saved Value Restricted to Authorized Values ONLY | __Depth.GetAllowedValues( ) (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) |
##
## MyClass Test AccessorFunc Implementation for Dynamic 1-line Parameters
##
class AccessorFuncDemoClassBase( ):
pass
class AccessorFuncDemoClass( AccessorFuncDemoClassBase ):
__Name = AccessorFuncBase( parent = AccessorFuncDemoClassBase, name = 'Name', default = 'AccessorFuncDemoClass', allowed_types = ( TYPE_STRING ), allowed_values = VALUE_ANY, documentation = 'Name Docs', getter_prefix = 'Get', key = 'Name', allow_erroneous_default = False, options = { } )
__x = AccessorFuncBase( parent = AccessorFuncDemoClassBase, name = 'X', default = 1111, allowed_types = ( TYPE_INTEGER, TYPE_FLOAT ), allowed_values = VALUE_ANY, documentation = 'X Docs', getter_prefix = 'Get', key = 'x', allow_erroneous_default = False, options = { } )
__Height = AccessorFuncBase( parent = AccessorFuncDemoClassBase, name = 'Height', default = 0, allowed_types = TYPE_INTEGER, allowed_values = VALUE_SINGLE_DIGITS, documentation = 'Height Docs', getter_prefix = 'Get', key = 'Height', allow_erroneous_default = False, options = { } )
# This is my humble contribution, extending the idea to serialize
# data from and to tuples, comparison operations and allowing functions
# as default values.
def Struct(*args, **kwargs):
FUNCTIONS = (types.BuiltinFunctionType, types.BuiltinMethodType, \
types.FunctionType, types.MethodType)
def init(self, *iargs, **ikwargs):
"""Asume that unamed args are placed in the same order than
astuple() yields (currently alphabetic order)
"""
kw = list(self.__slots__)
# set the unnamed args
for i in range(len(iargs)):
k = kw.pop(0)
setattr(self, k, iargs[i])
# set the named args
for k, v in ikwargs.items():
setattr(self, k, v)
kw.remove(k)
# set default values
for k in kw:
v = kwargs[k]
if isinstance(v, FUNCTIONS):
v = v()
setattr(self, k, v)
def astuple(self):
return tuple([getattr(self, k) for k in self.__slots__])
def __str__(self):
data = ['{}={}'.format(k, getattr(self, k)) for k in self.__slots__]
return '<{}: {}>'.format(self.__class__.__name__, ', '.join(data))
def __repr__(self):
return str(self)
def __eq__(self, other):
return self.astuple() == other.astuple()
name = kwargs.pop("__name__", "MyStruct")
slots = list(args)
slots.extend(kwargs.keys())
# set non-specific default values to None
kwargs.update(dict((k, None) for k in args))
return type(name, (object,), {
'__init__': init,
'__slots__': tuple(slots),
'astuple': astuple,
'__str__': __str__,
'__repr__': __repr__,
'__eq__': __eq__,
})
Event = Struct('user', 'cmd', \
'arg1', 'arg2', \
date=time.time, \
__name__='Event')
aa = Event('pepe', 77)
print(aa)
raw = aa.astuple()
bb = Event(*raw)
print(bb)
if aa == bb:
print('Are equals')
cc = Event(cmd='foo')
print(cc)
<Event: user=pepe, cmd=77, arg1=None, arg2=None, date=1550051398.3651814>
<Event: user=pepe, cmd=77, arg1=None, arg2=None, date=1550051398.3651814>
Are equals
<Event: user=None, cmd=foo, arg1=None, arg2=None, date=1550051403.7938335>
#!/usr/local/bin/python3
INITS = { 'ab': 100, 'cd': 200 }
class DP(dict):
def __init__(self):
super().__init__()
for k,v in INITS.items():
self[k] = v
def _dict_set(dp, key, value):
dp[key] = value
for item in INITS.keys():
setattr(
DP,
item,
lambda key: property(
lambda self: self[key], lambda self, value: _dict_set(self, key, value)
)(item)
)
a = DP()
print(a) # {'ab': 100, 'cd': 200}
a.ab = 'ab100'
a.cd = False
print(a.ab, a.cd) # ab100 False
class C:
def __init__(self):
self._x=None
def g(self):
return self._x
def s(self, x):
self._x = x
def d(self):
del self._x
def s2(self,x):
self._x=x+x
x=property(g,s,d)
c = C()
c.x="a"
print(c.x)
C.x=property(C.g, C.s2)
C.x=C.x.deleter(C.d)
c2 = C()
c2.x="a"
print(c2.x)
a
aa
class X:
def __init__(self, a=0, b=0, c=0):
self.a = a
self.b = b
self.c = c
@classmethod
def _make_properties(cls, field_name, inc):
_inc = inc
def _get_properties(self):
if not hasattr(self, '_%s_inc' % field_name):
setattr(self, '_%s_inc' % field_name, _inc)
inc = _inc
else:
inc = getattr(self, '_%s_inc' % field_name)
return getattr(self, field_name) + inc
def _set_properties(self, value):
setattr(self, '_%s_inc' % field_name, value)
return property(_get_properties, _set_properties)
for inc, field in enumerate(['a', 'b', 'c']):
setattr(X, '%s_summed' % field, X._make_properties(field, inc))
x = X()
assert x.a == 0
assert x.b == 0
assert x.c == 0
assert x.a_summed == 0 # enumerate() set inc to 0 + 0 = 0
assert x.b_summed == 1 # enumerate() set inc to 1 + 0 = 1
assert x.c_summed == 2 # enumerate() set inc to 2 + 0 = 2
# we set the variables to something
x.a = 1
x.b = 2
x.c = 3
assert x.a_summed == 1 # enumerate() set inc to 0 + 1 = 1
assert x.b_summed == 3 # enumerate() set inc to 1 + 2 = 3
assert x.c_summed == 5 # enumerate() set inc to 2 + 3 = 5
# we're changing the inc now
x.a_summed = 1
x.b_summed = 3
x.c_summed = 5
assert x.a_summed == 2 # we set inc to 1 + the property was 1 = 2
assert x.b_summed == 5 # we set inc to 3 + the property was 2 = 5
assert x.c_summed == 8 # we set inc to 5 + the property was 3 = 8
setattr(SomeClass, 'propertyName', property(getter, setter))
#!/usr/bin/python3
class Counter:
def __init__(self):
cls = self.__class__
self._count = 0
cls.count = self.count_ref()
def count_get(self):
print(f'count_get: {self._count}')
return self._count
def count_set(self, value):
self._count = value
print(f'count_set: {self._count}')
def count_del(self):
print(f'count_del: {self._count}')
def count_ref(self):
cls = self.__class__
return property(fget=cls.count_get, fset=cls.count_set, fdel=cls.count_del)
counter = Counter()
counter.count
for i in range(5):
counter.count = i
del counter.count
'''
output
======
count_get: 0
count_set: 0
count_set: 1
count_set: 2
count_set: 3
count_set: 4
count_del: 4
'''