方法一：json.dumps() ,不管字典里是单引号还是双引号，都可以用json.dumps()转换成字符串，且转后都为双引号！

import json
a = {'name':'lily','age':18}
b = {"name":"lily","age":18}
print(json.dumps(a))
print(json.dumps(b))
{"name": "lily", "age": 18}
{"name": "lily", "age": 18}
方法二：str ()，用str将字典转成字符串后，双引号变成了单引号
 
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a = {'name':'lily','age':18}
b = {"name":"lily","age":18}
print('a:',str(a))
print('b:',str(b))
a: {'name': 'lily', 'age': 18}
b: {'name': 'lily', 'age': 18}
二、字符串 转 字典
 
方法一、json.loads() ,要求json串格式中必须的双引号！！！转后双引号变为单引号
 
import json
a = {'name':'lily','age':18}
c = json.dumps(a)
print('c=',c)
print(json.loads(c))
c= {"name": "lily", "age": 18}
{'name': 'lily', 'age': 18}
json串为单引号时，用json.loads()会报错：由于json的key没有双引号，导致json解析错误的
 
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a = {"name":"lily","age":18}
d = str(a)
print('d=',d)
print(json.loads(d))
返回报错信息
d= {'name': 'lily', 'age': 18}
Traceback (most recent call last):
  File "/Users/PycharmProjects/FirstScrip/lijun/op_json.py", line 14, in <module>
    print(json.loads(d))
  File "/Users/anaconda3/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/Users/anaconda3/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/Users/anaconda3/lib/python3.6/json/decoder.py", line 355, in raw_decode
    obj, end = self.scan_once(s, idx)
json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 1 column 2 (char 1)