python dict更新差異

Question

python是否具有任何內置功能，可以通知在dict更新時更改了哪些字典元素？ 例如，我正在尋找這樣的功能：

>>> a = {'a':'hamburger', 'b':'fries', 'c':'coke'}
>>> b = {'b':'fries', 'c':'pepsi', 'd':'ice cream'}
>>> a.diff(b)
{'c':'pepsi', 'd':'ice cream'}
>>> a.update(b)
>>> a
{'a':'hamburger', 'b':'fries', 'c':'pepsi', 'd':'ice cream'}

我希望得到一個更改值的字典，如a.diff（b）的結果所示

Answer 1

不，但您可以繼承dict以提供有關更改的通知。

class ObservableDict( dict ):
    def __init__( self, *args, **kw ):
        self.observers= []
        super( ObservableDict, self ).__init__( *args, **kw )
    def observe( self, observer ):
        self.observers.append( observer )
    def __setitem__( self, key, value ):
        for o in self.observers:
            o.notify( self, key, self[key], value )
        super( ObservableDict, self ).__setitem__( key, value )
    def update( self, anotherDict ):
        for k in anotherDict:
            self[k]= anotherDict[k]

class Watcher( object ):
    def notify( self, observable, key, old, new ):
        print "Change to ", observable, "at", key

w= Watcher()
a= ObservableDict( {'a':'hamburger', 'b':'fries', 'c':'coke'} )
a.observe( w )
b = {'b':'fries', 'c':'pepsi'}
a.update( b )

請注意，此處定義的超類Watcher不檢查是否存在“真實”更改; 它只是注意到有一個變化。

Answer 2

一年之后

我喜歡以下解決方案：

>>> def dictdiff(d1, d2):                                              
        return dict(set(d2.iteritems()) - set(d1.iteritems()))
... 
>>> a = {'a':'hamburger', 'b':'fries', 'c':'coke'}
>>> b = {'b':'fries', 'c':'pepsi', 'd':'ice cream'}
>>> dictdiff(a, b)
{'c': 'pepsi', 'd': 'ice cream'}

Answer 3

不，它沒有。 但是編寫字典diff函數並不難：

def diff(a, b):
  diff = {}
  for key in b.keys():
    if (not a.has_key(key)) or (a.has_key(key) and a[key] != b[key]):
      diff[key] = b[key]
  return diff

Answer 4

簡單的差異功能很容易編寫。 根據您需要它的頻率，它可能比S.Lott更優雅的ObservableDict更快。

def dict_diff(a, b):
    """Return differences from dictionaries a to b.

    Return a tuple of three dicts: (removed, added, changed).
    'removed' has all keys and values removed from a. 'added' has
    all keys and values that were added to b. 'changed' has all
    keys and their values in b that are different from the corresponding
    key in a.

    """

    removed = dict()
    added = dict()
    changed = dict()

    for key, value in a.iteritems():
        if key not in b:
            removed[key] = value
        elif b[key] != value:
            changed[key] = b[key]
    for key, value in b.iteritems():
        if key not in a:
            added[key] = value
    return removed, added, changed

if __name__ == "__main__":
    print dict_diff({'foo': 1, 'bar': 2, 'yo': 4 }, 
                    {'foo': 0, 'foobar': 3, 'yo': 4 })

Answer 5

def diff_update(dict_to_update, updater):
    changes=dict((k,updater[k]) for k in filter(lambda k:(k not in dict_to_update or updater[k] != dict_to_update[k]), updater.iterkeys()))
    dict_to_update.update(updater)
    return changes

a = {'a':'hamburger', 'b':'fries', 'c':'coke'}
b = {'b':'fries', 'c':'pepsi'}
>>> print diff_update(a, b)
{'c': 'pepsi'}
>>> print a
{'a': 'hamburger', 'c': 'pepsi', 'b': 'fries'}

Answer 6

不是內置的，但你可以迭代字典的鍵並進行比較。 可能會很慢。

更好的解決方案可能是構建更復雜的數據結構並使用字典作為底層表示。