与值不同，字典需要在字典中有一个唯一的键，因此我们必须将反向的值附加到一个sort列表中，以便包含在新的特定键中。

def r_maping(dictionary):
    List_z=[]
    Map= {}
    for z, x in dictionary.iteritems(): #iterate through the keys and values
        Map.setdefault(x,List_z).append(z) #Setdefault is the same as dict[key]=default."The method returns the key value available in the dictionary and if given key is not available then it will return provided default value. Afterward, we will append into the default list our new values for the specific key.
    return Map

如果my_map中的值不是唯一的:

Python 3:

inv_map = {}
for k, v in my_map.items():
    inv_map[v] = inv_map.get(v, []) + [k]

Python 2:

inv_map = {}
for k, v in my_map.iteritems():
    inv_map[v] = inv_map.get(v, []) + [k]

要做到这一点，同时保留映射的类型(假设它是一个dict或dict子类):

def inverse_mapping(f):
    return f.__class__(map(reversed, f.items()))

我会在python2中这样做。

inv_map = {my_map[x] : x for x in my_map}

函数对于list类型的值是对称的;执行reverse_dict(reverse_dict(dictionary))时，元组被转换为列表

def reverse_dict(dictionary):
    reverse_dict = {}
    for key, value in dictionary.iteritems():
        if not isinstance(value, (list, tuple)):
            value = [value]
        for val in value:
            reverse_dict[val] = reverse_dict.get(val, [])
            reverse_dict[val].append(key)
    for key, value in reverse_dict.iteritems():
        if len(value) == 1:
            reverse_dict[key] = value[0]
    return reverse_dict

字典值为集合的一种情况。如:

some_dict = {"1":{"a","b","c"},
        "2":{"d","e","f"},
        "3":{"g","h","i"}}

逆函数是:

some_dict = {vi: k  for k, v in some_dict.items() for vi in v}

输出如下:

{'c': '1',
 'b': '1',
 'a': '1',
 'f': '2',
 'd': '2',
 'e': '2',
 'g': '3',
 'h': '3',
 'i': '3'}