JSON The format is Website and API Common standard format used , Now some mainstream databases （ Such as PostgreSQL） All support JSON Format . In this paper , We will show you how to use Python Handle JSON data . You can also go to our official Chinese website Oxylabs.cn For more information . First , Let's see JSON The definition of .
JSON or JavaScript Object Notation, It's a kind of Use text to store the format of data objects . let me put it another way , It is a kind of data structure , Express the object in text form . Although it comes from JavaScript, But it has become the actual standard for transmission objects .
Most popular programming languages support JSON Format , Include Python.JSON Format files are often used for API Transfer data objects . Here are JSON An example of a string ：
{
"name": "United States",
"population": 331002651,
"capital": "Washington D.C.",
"languages": [
"English",
"Spanish"
]
}In this case ,JSON The data looks like a Python Dictionaries . Like a dictionary ,JSON Pass data in the form of key value pairs . However ,JSON Data can also be character string 、 Numbers 、 Boolean or list .
stay JSON Before it became popular ,XML It has always been a common choice to represent data objects in text format . Here are XML An example of the same information in the format ：
<?xml version="1.0" encoding="UTF-8"?>
<country>
<name>United States</name>
<population>331002651</population>
<capital>Washington D.C.</capital>
<languages>
<language>English</language>
<language>Spanish</language>
</languages>
</country>Obviously ,JSON Less code . This is a JSON One of the main reasons for this popularity . If you want to know about JSON More information on Standards , Please visit JSON Official website .
Python Native support JSON data .Python json Modules are part of the standard library . The json The module can JSON Data from JSON Format conversion to equivalent Python object , for example dictionary and list.JSON The module can also put Python Object to JSON Format .
Python Of json The module provides the function of writing custom encoder and decoder , No separate installation required . You can go to This link Found in Pythonjson Official documentation of the module .
Next , We will study this module . We will JSON Convert to dictionary and list. We will also try to deal with custom classes .
JSON Data is often stored in character string in . This is the use of API Common scenarios when .JSON Data is usually stored in string variables before parsing . therefore , And JSON The most common related task is to JSON The string resolves to Python Dictionaries .JSON The module can easily handle this task .
The first step is to import Python Of json modular . This module contains two important functions -loads and load.
Please note that , The first method looks like the plural form , But that's not the case . Letter “S” representative “ character string ”.
loads Is to parse a string into JSON data . Please note that , It reads “load-s”. there “s” representative “ character string ”.Load The usage scenario of is When data is in bytes . This part will be described in detail later .
Let's start with a simple example .JSON Data examples are as follows ：
{
"name": "United States",
"population": 331002651,
}JSON Data can be stored as before parsing JSON character string . Not only can we use it Python Of Three quotes To store multiple lines of string , It can also be done through Remove line breaks To improve readability .
# JSON string
country = '{"name": "United States", "population": 331002651}'
print(type(country))The output of this code snippet will confirm that this is indeed a JSON character string ：
<class 'str'>We can call this json.loads() And take this string as a parameter .
import json
country = '{"name": "United States", "population": 331002651}'
country_dict = json.loads(country)
print(type(country))
print(type(country_dict))The output of this code snippet will confirm... As a string JSON The data is now Python Dictionaries .
<class 'str'>
<class 'dict'>This dictionary can be accessed as usual ：
print(country_dict['name'])
# OUTPUT: United StatesIt should be noted that ,json.loads() Methods do not always return dictionaries . The data type returned will Depends on the input string . for example , The following JSON The string will return a list , Not a dictionary .
countries = '["United States", "Canada"]'
counties_list= json.loads(countries)
print(type(counties_list))
# OUTPUT: Again , If JSON The string contains true, It will be converted to Python Equivalent Boolean value , namely True.
import json
bool_string = 'true'
bool_type = json.loads(bool_string)
print(bool_type)
# OUTPUT: TrueThe following table shows Converted JSON Objects and Python data type .
JSON
Python
object
dict
array
list
string
str
number (integer)
int
number (real)
float
true
True
false
False
null
None
Next we will move on to the next topic , take JSON The object resolves to Python object .
Read JSON file , And will JSON The data is parsed as Python data , Parse with us stored in string JSON The way the data is processed is very similar . except JSON, We also need Python The native function of open().
commonly loads For reading JSON character string , and load() Used to read... In a file JSON data .
load() Method receives a file object and returns a file object that resolves to Python Object's JSON data .
To get the file object from the file path , have access to Python Function of open().
Add the following JSON Save the data as a new file and name it united_states.json：
{
"name": "United States",
"population": 331002651,
"capital": "Washington D.C.",
"languages": [
"English",
"Spanish"
]
}Enter this... In the new file Python Script ：
import json
with open('united_states.json') as f:
data = json.load(f)
print(type(data))Run this Python The file outputs the following ：
<class 'dict'>In this example , The open Function returns a file handle , This handle is provided to load.
Variable data contain JSON, As Python Dictionaries . This means that the dictionary keys can be checked as follows ：
print(data.keys())
# OUTPUT: dict_keys(['name', 'population', 'capital', 'languages'])Use this information ,name You can output the following ：
data['name']
# OUTPUT: United StatesIn the first two sections , We studied how to JSON Convert to Python object . Now? , Let's see how to put Python Object to JSON object .
take Python Object to JSON Objects are also called serialization or JSON code . You can use functions dumps() To achieve . It is read as dump-s, Letter S Representative string .
Here is a simple example . Use this code as Python The script is saved in a new file ：
import json
languages = ["English","French"]
country = {
"name": "Canada",
"population": 37742154,
"languages": languages,
"president": None,
}
country_string = json.dumps(country)
print(country_string)Use Python When running this file , The following results will be output ：
{"name": "Canada", "population": 37742154, "languages": ["English", "French"],
"president": null}Python The object is now a JSON Object . This simple example shows that Python The object resolves to JSON Object procedure , The whole process is not complicated . And here Python Object is a Dictionaries . This is how it is converted to JSON The reason for the object type . Again , Lists can also be converted to JSON. This is the corresponding Python Script and its output ：
import json
languages = ["English", "French"]
languages_string = json.dumps(languages)
print(languages_string)
# OUTPUT: ["English", "French"]It is not limited to dictionaries and lists .string,int,float,bool even to the extent that None Values can be converted to JSON.
For more information , Refer to the conversion table below . You can see , Only the dictionary is converted to json object type . Relevant official documents , see also This link .
Python
JSON
dict
object
list,tuple
array
str
string
int,float,int
number
True
true
False
false
None
null
Used for compiling JSON The way to file is dump(). This method and dumps() The method is very similar . The only difference is dumps() Returns a string ,dump() Write a file .
Here is a simple demonstration , The file will be opened in edit mode and the data will be written as JSON Format . Save this Python Script and run it .
import json
# Tuple is encoded to JSON array.
languages = ("English", "French")
# Dictionary is encoded to JSON object.
country = {
"name": "Canada",
"population": 37742154,
"languages": languages,
"president": None,
}
with open('countries_exported.json', 'w') as f:
json.dump(country, f)Use Python When executing this code ,countries_exported.json Will create （ Or cover ） file , The contents are as follows JSON file .
however , You will find the whole JSON All in one line . To make it more readable , We can pass another parameter to dump() function , As shown below ：
json.dump(country, f, indent=4)This time, , When you run code , The format is normal , It also indents 4 A space ：
{
"languages": [
"English",
"French"
],
"president": null,
"name": "Canada",
"population": 37742154
}Be careful ,indent Parameters can also be used for JSONdumps() Method .JSONdump() and JSONdumps() The only difference is dump() Need a file object .
Let's check dump() Method signature ：
dump(obj, fp, *, skipkeys=False, ensure_ascii=True, check_circular=True,allow_nan=True, cls=None, indent=None, separators=None,default=None, sort_keys=False, **kw)Focus on parameters cls.
If you're calling dump There is no Class, be dump() and dumps() Methods will default to JSONEncoder This kind . This class supports standard Python Type a ：dict,list,tuple,str,int,float,True,False, and None.
If we try json.loads() Call this method on any other type , This method will trigger TypeError Error message ：Object of typeis not JSON serializable.
Save the following code as Python Script and run ：
import json
class Country:
def __init__(self, name, population, languages):
self.name = name
self.population = population
self.languages = languages
canada = Country("Canada", 37742154, ["English", "French"])
print(json.dumps(canada))
# OUTPUT: TypeError: Object of type Country is not JSON serializableTo convert an object to JSON, We need to write an extension JSONEncoder A new class of . In this class , Need to achieve default(). This method will have a return JSON Custom code for .
Here are Country Class . This class will help you Python Object to JSON object ：
import json
class CountryEncoder(json.JSONEncoder):
def default(self, o):
if isinstance(o, Country):
# JSON object would be a dictionary.
return {
"name" : o.name,
"population": o.population,
"languages": o.languages
}
else:
# Base class will raise the TypeError.
return super().default(o)This code confirms that the provided object is Country Class will return a dictionary , Or call the parent to handle the rest .
This class can be provided to json.dump() and json.dumps() Method .
print(json.dumps(canada, cls=CountryEncoder))
# OUTPUT: {“name": "Canada", "population": 37742154, "languages": ["English", "French"]}up to now , We have discussed how to use json.load() and json.loads() Method to create a dictionary 、 List etc. . If we want to read JSON Object and create a custom class object ？
In this section , We will Create a custom JSON decoder , Help us create custom objects . This custom decoder will allow us to use json.load() and json.loads() Method , And return a custom class object .
We will use the Country class . Use custom encoder , We can write the following code ：
# Create an object of class Country
canada = Country("Canada", 37742154, ["English", "French"])
# Use json.dump() to create a JSON file in writing mode
with open('canada.json','w') as f:
json.dump(canada,f, cls=CountryEncoder)If we try to use json.load() Method to parse this JSON file , We will get a dictionary ：
with open('canada.json','r') as f:
country_object = json.load(f)
# OUTPUT: <type ‘dict'="">If you want to get Country Class instead of a dictionary , We need to create one Custom decoder . This decoder class will Expand JSONDecoder. In this class , We're going to write object_hook. This allows you to read values from the dictionary to create Country Class object .
In addition to writing this , We also need to call __init__ Base class And the parameter object_hook Set the value of to the name of the method . For the sake of simplicity , We can use the same name .
import json
class CountryDecoder(json.JSONDecoder):
def __init__(self, object_hook=None,
*args, **kwargs):
super().__init__(object_hook=self.object
_hook, *args, **kwargs)
def object_hook(self, o):
decoded_country = Country(
o.get('name'),
o.get('population'),
o.get('languages'),
)
return decoded_countryBe careful , We will use .get() Method to read dictionary keys . This will ensure that an error is not raised when a key is missing from the dictionary .
Last , We can call json.load() Methods and cls Parameter set to CountryDecoder class .
with open('canada.json','r') as f:
country_object = json.load(f, cls=CountryDecoder)
print(type(country_object))
# OUTPUT: <class ‘country'="">Get it done ！ We now have a direct from JSON Created a custom object .
Python Of JSON The module has four main functions ：read(),reads(),load(), and loads(). These features are often confusing . The most important thing is Letter “s” representative String. in addition , In function loads() and dumps() Letters in “s” need Read separately , namely loads read load-s,dumps() read dump-s.
This is a quick form , Can help you remember these functions ：
_
File
String
Read
load()
loads()
Write
dump()
dumps()
In this tutorial , We learned to use Python Read and write JSON data . Especially when dealing with websites , Learn how to handle JSON Data is crucial .JSON It is used to transmit and store data in many places , Include API、 Web crawlers and modern databases （ Such as PostgreSQL）.
If you are working on a web crawl project involving dynamic websites , So understanding JSON crucial . You can read our article , understand JSON Application of instance in infinite scrolling page .
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