Python JSON operation - conversion between JSON, python objects, and custom objects

Preface

API When testing ,Request Body and Response Body The format could be JSON Format , So for JSON It is very important to deal with . About JSON Please refer to this article for the concept of 《REST Assured 22 - JSON》

Python Yes JSON The operation of is very convenient , There are mainly the following 4 A way .

Method function json.dumps() take Python The object is encoded as JSON character string json.loads() To encode JSON The string is decoded to Python object json.dump() take Python The built-in type is serialized as json After the object write file json.load() Read the file in json The string element of form is converted to Python type

Summary ：

1. json.dumps() practice
2. json.loads() practice
3. json.dump() practice
4. json.loads() practice
5. How to dynamically set JSON request body

Python The object is encoded as JSON character string json.dumps()

1. Dictionaries dict Turn it into JSON

import json
d = {
"key1" : "value1", "key2" : "value2"}
json_string = json.dumps(d)
print("dic: {}".format(d))
print("json string: {}".format(json_string))

Output ：
dict in key/value All are Single quotation marks Of ,json Medium key/value yes Double quotes Of .

dic: {
'key1': 'value1', 'key2': 'value2'}
json string: {
"key1": "value1", "key2": "value2"}

2. Format output JSON
Control indent ,key value Connector between

import json
d = {
"key1" : "value1", "key2" : "value2"}
json_string_pretty_1 = json.dumps(d, indent=2, separators=(',', ':'))
json_string_pretty_2 = json.dumps(d, indent=4, separators=(',', '='))
print("json string pretty 1 :\n {}".format(json_string_pretty_1))
print("json string pretty 2 :\n {}".format(json_string_pretty_2))

Output ： Two different formats

json string pretty 1 :
{

"key1":"value1",
"key2":"value2"
}
json string pretty 2 :
{

"key1"="value1",
"key2"="value2"
}

3. Press Key Sort output JSON character string
sort_keys=True Press key Sort

import json
d_dis_order = {
"name" : "peter", "age": 18, "gender" : "men"}
json_in_order = json.dumps(d_no_order, indent=4, sort_keys=True)
print("dic disorder:\n {}".format(d_dis_order))
print("json string inorder:\n {}".format(json_in_order))

Output ：

dic disorder:
{
'name': 'peter', 'age': 18, 'gender': 'man'}
json string inorder:
{

"age": 18,
"gender": "man",
"name": "peter"
}

4. Convert the class object to JSON character string
Custom objects are converted to JSON character string , You need to customize one JSONEncoder Subclass to override the default Serialization is assigned to cls Parameters .

To use a custom JSONEncoder subclass (e.g. one that overrides the .default() method to serialize additional types), specify it with the cls kwarg; otherwise JSONEncoder is used.

import json
from json import JSONEncoder
class Person:
def __init__(self, name, age, gender):
self.name = name
self.age = age
self.gender = gender
class PersonEncoder(JSONEncoder):
def default(self, o):
return o.__dict__
peter = Person("Peter", 18, "Men")
json_peter = json.dumps(peter, indent=4, cls=PersonEncoder)
print("peter object:\n{}".format(peter))
print("json peter:\n{}".format(json_peter))

Output ：

peter object:
<__main__.Person object at 0x000001FE156C9648>
json peter:
{

"name": "Peter",
"age": 18,
"gender": "Men"
}

JSON The string is decoded to Python object json.loads()

1. visit JSON The value in
adopt json.loads() Methods will JSON String to python Of dict Object can access its key value

import json
json_string = '''{"name":"peter", "age":18, "gender":"Men"}'''
data = json.loads(json_string)
print("json string:\n{}".format(json_string))
print("data:\n{}".format(data))
print("age: {}".format(data["age"]))

Output ：

json string:
{
"name":"peter", "age":18, "gender":"Men"}
data:
{
'name': 'peter', 'age': 18, 'gender': 'Men'}
age: 18

2. visit JSON Nested objects

obtain JSON In a string salary Value

import json
json_string = ''' { "company": { "person": { "name": "peter", "age": 18, "gender": "Men", "pay": { "salary": 3000, "bonus": 5000 } } } } '''
data = json.loads(json_string)
print("json string:\n{}".format(json_string))
print("data:\n{}".format(data))
print("salary: {}".format(data["company"]["person"]["pay"]["salary"]))

Output ：
adopt data[“company”][“person”][“pay”][“salary”] Accessing nested values

json string:
{

"company": {

"person": {

"name": "peter",
"age": 18,
"gender": "Men",
"pay": {

"salary": 3000,
"bonus": 5000
}
}
}
}
data:
{
'company': {
'person': {
'name': 'peter', 'age': 18, 'gender': 'Men', 'pay': {
'salary': 3000, 'bonus': 5000}}}}
salary: 3000

3. take JSON String into class object
object_hook Is used to JSON The string is decoded into a custom class object , Default object_hook= None Is decoded into dict. So you need to customize a decoding method .

object_hook is an optional function that will be called with the result of any object literal decode (a dict). The return value of object_hook will be used instead of the dict. This feature can be used to implement custom decoders (e.g. JSON-RPC class hinting).

import json
class Person:
def __init__(self, name, age, gender):
self.name = name
self.age = age
self.gender = gender
def PersonDecoder(obj):
return Person(obj['name'], obj['age'], obj['gender'])
person_json_string = '''{"name" : "peter", "age": 18, "gender" : "men"}'''
person_object = json.loads(person_json_string, object_hook=PersonDecoder)
print("person json string:\n{}".format(person_json_string))
print("peson object:\n{}".format(person_object))
print("name:{}\nage:{}\ngender:{}".format(person_object.name, person_object.age, person_object.gender))

Output ：

person json string:
{
"name" : "peter", "age": 18, "gender" : "men"}
peson object:
<__main__.Person object at 0x000001FFBCF4AA88>
name:peter
age:18
gender:men

4. Judge JSON Is the format correct

The following JSON String One less. ’ } '

json_string = ''' { "company": { "person": { "name": "peter", "age": 18, "gender": "Men", "pay": { "salary": 3000, "bonus": 5000 } } } '''
def is_valid_JSON(json_data):
try:
json.loads(json_data)
except ValueError as err:
return False
return True
is_valid = is_valid_JSON(json_string)
print("json string is valid: {}".format(is_valid))

Output ：

json string is valid: False

5. obtain JSON One of the strings key All the values

Get the following JSON All in string name Of value

import json
json_string = ''' [ { "id":1, "name":"peter", "hobby":[ "reading", "movie" ] }, { "id":2, "name":"lina", "hobby":[ "sleep", "shopping" ] } ] '''
json_data = json.loads(json_string)
name_list = [item.get("name") for item in json_data]
print(name_list)

Output ：

['peter', 'lina']

take Python The built-in type is serialized as json After the object write file json.dump()

1. Dictionaries dict Turn it into JSON write file

import json
d = {
"name" : "peter", "age": 18, "gender" : "men"}
with open("json.txt", 'w+') as f:
json.dump(d, f, indent=4)

json.txt Content

2. Custom class objects are converted to JSON Write text
You need to customize one JSONEncoder Subclass to override the default Serialization is assigned to cls Parameters .

import json
from json import JSONEncoder
class Person:
def __init__(self, name, age, gender):
self.name = name
self.age = age
self.gender = gender
class PersonEncoder(JSONEncoder):
def default(self, o):
return o.__dict__
person = Person("peter", 18, "men")
with open("json.txt", 'w+') as f:
json.dump(d, f, indent=4, cls=PersonEncoder)

json.txt Content

Read the file in json The string element of form is converted to Python type json.load()

1. In the text json String to dict

with open("json.txt", 'r') as f:
data = json.load(f)
print(data)

Output ：

{
'name': 'peter', 'age': 18, 'gender': 'men'}

2. In text json String into a custom class object
object_hook Is used to JSON The string is decoded into a custom class object , Default object_hook= None Is decoded into dict. So you need to customize a decoding method .

import json
class Person:
def __init__(self, name, age, gender):
self.name = name
self.age = age
self.gender = gender
def PersonDecoder(obj):
return Person(obj['name'], obj['age'], obj['gender'])
with open("json.txt", 'r') as f:
person = json.load(f, object_hook=PersonDecoder)
print("name:{}\nage:{}\ngender:{}".format(person.name, person.age, person.gender))

How to dynamically set JSON request body

Sometimes we put json Of request In a text file , But not every request is fixed json body, You need to dynamically modify the values , Finally, it has to be transformed into json String as request body.

for example ：json.txt Content of text
Need modification collection-id Value of field , Change the json String input request As body

Be careful ：json body key They are all in double quotation marks , So make sure that python The object of is transformed into json character string , To pass in request.

{

"search": {

"query": {

"collection-id": ["collection"]
}
},
"targets": [
{

"type": "subscription-id",
"value": [
1234
]
}
]
}

import json
with open("json.txt", 'r') as f:
data = json.load(f)
print("data:\n{}".format(data))
data["search"]["query"]["collection-id"] = ["collection_1", "collection_2", "collection_3"]
print("new data:\n{}".format(data))
json_data = json.dumps(data, indent=4)
print("json data:\n{}".format(json_data))

Output ：

data:
{
'search': {
'query': {
'collection-id': ['collection']}}, 'targets': [{
'type': 'subscription-id', 'value': [1234]}]}
new data:
{
'search': {
'query': {
'collection-id': ['collection_1', 'collection_2', 'collection_3']}}, 'targets': [{
'type': 'subscription-id', 'value': [1234]}]}
json data:
{

"search": {

"query": {

"collection-id": [
"collection_1",
"collection_2",
"collection_3"
]
}
},
"targets": [
{

"type": "subscription-id",
"value": [
1234
]
}
]
}