Python——找出内层字典中所用到的全部键，并以集合的形式返回。

'''
3. 编写一个叫做db_headings的函数，要求能够找出内层字典中所用到的全部键，并以集合的形式返回。
以给出的字典为例，该函数应该返回集合{'author', 'forename', 'born', 'surname', 'notes', 'died'}。


{
    'jgoodall':{'surname':'goodall',
                'forename':'Jane',
                'born':1934,
                'died':None,
                'notes':'primate researcher',
                'author':['In the Shadow of Man','The Chimpanzees of Gombe']},
    'rfranklin':{'surname':'Franklin',
                 'forename':'Rosalind',
                 'born':1920,
                 'died':1957,
                 'notes':'contributed to discovery of DNA'},
    'rcarson':{'surname':'Carson',
               'forename':'rachel',
               'born':1907,
               'died':1964,
               'notes':'raised awareness of effects of DDT',
               'author':['Silent Sporing']}
    }
'''
def db_headings():
    people = {
    'jgoodall':{'surname':'goodall',
                'forename':'Jane',
                'born':1934,
                'died':None,
                'notes':'primate researcher',
                'author':['In the Shadow of Man','The Chimpanzees of Gombe']},
    'rfranklin':{'surname':'Franklin',
                 'forename':'Rosalind',
                 'born':1920,
                 'died':1957,
                 'notes':'contributed to discovery of DNA'},
    'rcarson':{'surname':'Carson',
               'forename':'rachel',
               'born':1907,
               'died':1964,
               'notes':'raised awareness of effects of DDT',
               'author':['Silent Sporing']}
    }
    l=[]
    for name in people.values():
        a = name
        for name in a.keys():
            l.append(name)
    n=[]
    for i in l:
        if i not in n:
             n.append(i)
    print(n)
db_headings()



'''
#创建一个存储一个学生的信息，通过遍历可以取出所有信息
student={'name':'xiaoming','age':11,'school':'tsinghua'}
for key,value in student.items():
    print(key+':'+str(value))

输出： 
age:11 
name:xiaoming 
school:tsinghua
注意： 
遍历出的返回值输出和存储的顺序不一样，输出顺序每次都会变化 
在for循环中key和value两个变量需要使用逗号‘，’隔开


#取键
student = {'name': 'xiaoming', 'age': 11, 'school': 'tsinghua'}
    for name in student.keys():
        print(name)
输出   
name
age
school


#keys()返回的值顺序是不确定的，如果想按序排列，可以使用sorted()进行排序
for name in sorted(people.keys()):
'''