我正在努力解决 Python 中的一个小问题（我的程序现在是 3.2.3 版）。
我有一本看起来像这样的字典（这只是一个例子，实际上取自这里的另一篇文章）：
[
{"abc": "movies"},
{"abc": "sports"},
{"abc": "music"},
{"xyz": "music"},
{"pqr": "music"},
{"pqr": "movies"},
{"pqr": "sports"},
{"pqr": "news"},
{"pqr": "sports"},
]
我想简单地 print() 一个唯一值列表，消除重复项。在此列表的末尾，我想打印字典中唯一值的数量：
movies
sports
music
news
4
任何帮助表示赞赏。我发现这里还有一些其他的帖子有些相关，但我对 Python 的了解还不够，无法将其应用于这个特定问题。
在这里使用set，因为它们只包含独特的项目。
>>> lis = [{"abc":"movies"}, {"abc": "sports"}, {"abc": "music"}, {"xyz": "music"}, {"pqr":"music"}, {"pqr":"movies"},{"pqr":"sports"}, {"pqr":"news"}, {"pqr":"sports"}]
>>> s = set( val for dic in lis for val in dic.values())
>>> s
set(['movies', 'news', 'music', 'sports'])
循环这个集合以获得预期的输出：
for x in s:
print x
print len(s) #print the length of set after the for-loop
...
movies
news
music
sports
4
这一行s = set( val for dic in lis for val in dic.values())大致相当于：
s = set()
for dic in lis:
for val in dic.values():
s.add(val)
You can exploit the properties of set for this purpose; each element is unique and duplicates will be ignored.
uniqueValues = set(myDict.values())
By using set in this way, duplicate elements returned from .values() will be discarded. You can then print them as follows:
for value in uniqueValues:
print(value)
print(len(uniqueValues))
使用set()：
from itertools import chain
unique_values = set(chain.from_iterable(d.values() for d in dictionaries_list))
for value in unique_values:
print(value)
print(len(unique_values))
在 Python 2 上使用.itervalues()可以提高效率。因为你有一个字典列表，我们需要首先从每个字典中提取值；我itertools.chain.from_iterable()与生成器表达式一起使用以列出序列中的所有值：
>>> for value in set(chain.from_iterable(d.values() for d in dictionaries_list)):
... print(value)
...
news
sports
movies
music
另一种方法是在生成器表达式中使用嵌套循环：
>>> for value in set(v for d in dictionaries_list for v in d.values()):
... print(value)
...
news
sports
movies
music
dict = {'511':'Vishnu','512':'Vishnu','513':'Ram','514':'Ram','515':'sita'}
list =[] # create empty list
for val in dict.values():
if val in list:
continue
else:
list.append(val)
print list