Python 如何检测字典中的任何元素是否发生更改？
而不是保存字典的副本，并比较新旧版本，如下所示：Python 如何检测字典中的任何元素是否发生更改？,python,dictionary,Python,Dictionary,而不是保存字典的副本，并比较新旧版本，如下所示： dict = { "apple":10, "pear":20 } if ( dict_old != dict ): do something dict_old = dict 如何检测字典中的任何元素何时发生更改？您可以将dict子类化，并包含一些自定义的\uuuuuuu setitem\uuuuu行为： class MyDict(dict): def __setitem__(self, item, value):
dict = { "apple":10, "pear":20 }
if ( dict_old != dict ):
do something
dict_old = dict
如何检测字典中的任何元素何时发生更改？您可以将
dict\uuuuuuu setitem\uuuuuclass MyDict(dict):
def __setitem__(self, item, value):
print "You are changing the value of %s to %s!!"%(item, value)
super(MyDict, self).__setitem__(item, value)
In [58]: %cpaste
Pasting code; enter '--' alone on the line to stop or use Ctrl-D.
:class MyDict(dict):
: def __setitem__(self, item, value):
: print "You are changing the value of %s to %s!!"%(item, value)
: super(MyDict, self).__setitem__(item, value)
:--
In [59]: d = MyDict({"apple":10, "pear":20})
In [60]: d
Out[60]: {'apple': 10, 'pear': 20}
In [61]: d["pear"] = 15
You are changing the value of pear to 15!!
In [62]: d
Out[62]: {'apple': 10, 'pear': 15}
printglobalslocalsdictMyDict\uuuuu setitem\uuuuuu然而，这是一件非常糟糕的事情。首先，这将涉及一些严重的
本地人全球人dict1==dict2我会给你分类的 比@EMS更进一步 子类
dictsentinalclass MyDict(dict):
def __init__(self):
super(MyDict, self).__init__
self.sentinal = list()
def __setitem__(self, item, value):
self.sentinal.append(item)
super(MyDict, self).__setitem__(item, value)
def __getitem__(self, item):
self.sentinal.remove(item)
return super(MyDict, self).__getitem__(item)
def update(self, iterable):
super(MyDict, self).update(iterable)
self.sentinal.extend(k for k, v in iterable)
def items(self):
self.sentinal = list()
return super(MyDict, self).items()
def iteritems(self):
self.sentinal = list()
return super(MyDict, self).iteritems()
def item_changed(self):
return bool(self.sentinal), self.sentinal
>>> d = MyDict()
>>> d.update(((i, i*i) for i in xrange(5)))
>>> d
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
>>> d[1] = 'g'
>>> d.item_changed()
(True, [1])
>>> z = d[1]
>>> d.item_changed()
(False, [])
>>> d[3] = 'b'
>>> d[4] = 'foo'
>>> d
{0: 0, 1: 'g', 2: 4, 3: 'b', 4: 'foo'}
>>> d.item_changed()
(True, [3, 4])
>>> d.items()
[(0, 0), (1, 'g'), (2, 4), (3, 'b'), (4, 'foo')]
>>> d.item_changed()
(False, [])
>>> d.update([(0, 'bar'), (2, 'baz')])
>>> d
{0: 'bar', 1: 'g', 2: 'baz', 3: 'b', 4: 'foo'}
>>> d.item_changed()
(True, [0, 2])
>>> list(d.iteritems())
foo
[(0, 'bar'), (1, 'g'), (2, 'baz'), (3, 'b'), (4, 'foo')]
>>> d.item_changed()
(False, [])
>>>
您可以创建一个观察者，它将监视数据内容是否已更改 下面的代码应该是不言自明的。它应该适用于嵌套的dict和list
"""Observer descriptor class allows to trigger out any arbitrary action, when the content of observed
data changes.
"""
import weakref
class Observer(object):
"""Observes attached data and trigger out given action if the content of data changes.
Observer is a descriptor, which means, it must be declared on the class definition level.
Example:
>>> def action(observer, instance, value):
... print 'Data has been modified: %s' % value
>>> class MyClass(object):
... important_data = Observer('init_value', callback=action)
>>> o = MyClass()
>>> o.important_data = 'new_value'
Data has been modified: new_value
Observer should work with any kind of built-in data types, but `dict` and `list` are strongly advice.
Example:
>>> class MyClass2(object):
... important_data = Observer({}, callback=action)
>>> o2 = MyClass2()
>>> o2.important_data['key1'] = {'item1': 'value1', 'item2': 'value2'}
Data has been modified: {'key1': {'item2': 'value2', 'item1': 'value1'}}
>>> o2.important_data['key1']['item1'] = range(5)
Data has been modified: {'key1': {'item2': 'value2', 'item1': [0, 1, 2, 3, 4]}}
>>> o2.important_data['key1']['item1'][0] = 'first'
Data has been modified: {'key1': {'item2': 'value2', 'item1': ['first', 1, 2, 3, 4]}}
Here is an example of using `Observer` as a base class.
Example:
>>> class AdvanceDescriptor(Observer):
... def action(self, instance, value):
... logger = instance.get_logger()
... logger.info(value)
...
... def __init__(self, additional_data=None, **kwargs):
... self.additional_data = additional_data
...
... super(AdvanceDescriptor, self).__init__(
... callback=AdvanceDescriptor.action,
... init_value={},
... additional_data=additional_data
... )
"""
def __init__(self, init_value=None, callback=None, **kwargs):
"""
Args:
init_value: initial value for data, if there is none
callback: callback function to evoke when the content of data will change; the signature of
the callback should be callback(observer, instance, value), where:
observer is an Observer object, with all additional data attached to it,
instance is an instance of the object, where the actual data lives,
value is the data itself.
**kwargs: additional arguments needed to make inheritance possible. See the example above, to get an
idea, how the proper inheritance should look like.
The main challenge here comes from the fact, that class constructor is used inside the class methods,
which is quite tricky, when you want to change the `__init__` function signature in derived classes.
"""
self.init_value = init_value
self.callback = callback
self.kwargs = kwargs
self.kwargs.update({
'callback': callback,
})
self._value = None
self._instance_to_name_mapping = {}
self._instance = None
self._parent_observer = None
self._value_parent = None
self._value_index = None
@property
def value(self):
"""Returns the content of attached data.
"""
return self._value
def _get_attr_name(self, instance):
"""To respect DRY methodology, we try to find out, what the original name of the descriptor is and
use it as instance variable to store actual data.
Args:
instance: instance of the object
Returns: (str): attribute name, where `Observer` will store the data
"""
if instance in self._instance_to_name_mapping:
return self._instance_to_name_mapping[instance]
for attr_name, attr_value in instance.__class__.__dict__.iteritems():
if attr_value is self:
self._instance_to_name_mapping[weakref.ref(instance)] = attr_name
return attr_name
def __get__(self, instance, owner):
attr_name = self._get_attr_name(instance)
attr_value = instance.__dict__.get(attr_name, self.init_value)
observer = self.__class__(**self.kwargs)
observer._value = attr_value
observer._instance = instance
return observer
def __set__(self, instance, value):
attr_name = self._get_attr_name(instance)
instance.__dict__[attr_name] = value
self._value = value
self._instance = instance
self.divulge()
def __getitem__(self, key):
observer = self.__class__(**self.kwargs)
observer._value = self._value[key]
observer._parent_observer = self
observer._value_parent = self._value
observer._value_index = key
return observer
def __setitem__(self, key, value):
self._value[key] = value
self.divulge()
def divulge(self):
"""Divulges that data content has been change calling callback.
"""
# we want to evoke the very first observer with complete set of data, not the nested one
if self._parent_observer:
self._parent_observer.divulge()
else:
if self.callback:
self.callback(self, self._instance, self._value)
def __getattr__(self, item):
"""Mock behaviour of data attach to `Observer`. If certain behaviour mutate attached data, additional
wrapper comes into play, evoking attached callback.
"""
def observe(o, f):
def wrapper(*args, **kwargs):
result = f(*args, **kwargs)
o.divulge()
return result
return wrapper
attr = getattr(self._value, item)
if item in (
['append', 'extend', 'insert', 'remove', 'pop', 'sort', 'reverse'] + # list methods
['clear', 'pop', 'update'] # dict methods
):
return observe(self, attr)
return attr
def action(self, instance, value):
print '>> log >', value, '<<'
class MyClass(object):
meta = Observer('', action)
mc1 = MyClass()
mc2 = MyClass()
mc1.meta = {
'a1': {
'a11': 'a11_val',
'a22': 'a22_val',
},
'b1': 'val_b1',
}
mc1.meta['a1']['a11'] = ['1', '2', '4']
mc1.meta['a1']['a11'].append('5')
mc1.meta.update({'new': 'new_value'})
mc2.meta = 'test'
mc2.meta = 'test2'
mc2.meta = range(10)
mc2.meta[5] = 'test3'
mc2.meta[9] = {
'a': 'va1',
'b': 'va2',
'c': 'va3',
'd': 'va4',
'e': 'va5',
}
mc2.meta[9]['a'] = 'val1_new'
class MyClass2(object):
pkg = Observer('', action)
mc3 = MyClass2()
mc3.pkg = 'test_myclass2'
print mc1.meta.value
checksum = make_hash(d)
def make_hash(d):
check = ''
for key in d:
check += str(d[key])
return hash(check)
if checksum != make_hash(d):
print('Dictionary changed')
>>> import jsonfile
>>> class DoSomething(jsonfile.JSONFileRoot):
... def on_change(self):
... print("do something")
...
>>> d = DoSomething({"apple": 10, "pear": 20})
>>> d.data["apple"] += 1
do something
>>> d.data
{'apple': 11, 'pear': 20}
>>> d.data["plum"] = 5
do something
>>> d.data
{'apple': 11, 'pear': 20, 'plum': 5}