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# JSON Dump
## Python JSON Dump To Or Load From File Example
August 19, 2018 \
Reference :
JSON is the standard data format that be used to save and transfer text data between programs. It is independent from programming language. Python provide built-in json module to process JSON string and Python object conversion. This article will give you some example.
#### 1. JSON String And Python Object Conversion Overview.
Before you can use json module, you should import it first.
```python
import json
```
**1.1 Convert Dict Object To JSON String.**
1. Create a dict object.
2. Call json.dumps() method to get JSON string from dict object.
```
import json
# Convert a python dict object to JSON string.
def python_dict_to_json_string():
# Create a dict object.
dict_object = dict(name='Richard', age=25, score=100)
# Call json.dumps method.
json_string = json.dumps(dict_object)
# Print JSON string in console.
print(json_string)
if __name__ == '__main__':
python_dict_to_json_string()
```
Below is the output.
```
{"name": "Richard", "age": 25, "score": 100}
```
**1.2 Convert JSON String To Dict Object.**
1. Create a JSON string.
2. Call json.loads() method to return the python dict object.
```python
import json
# Convert JSON string to python dict.
def python_json_string_to_dict():
# Create a JSON string.
json_string = '{"name": "Tom", "age" : 25, "score" : 100 }'
# Load the JSON string to python dict object.
dict_object = json.loads(json_string)
# Print dict value by key.
print(dict_object["name"])
print(dict_object["score"])
print(dict_object["age"])
if __name__ == '__main__':
python_json_string_to_dict()
```
Below is the output.
```
Tom
100
25
```
#### 2. Dump Python Dict To JSON File Or Load Dict From JSON File.
**2.1 Dump Dict To JSON File.**
1. Call open method to get a file object.
2. Call json.dump(dict\_object, file\_object) to save dict data to JSON file.
```python
import json
# Save a python dict object to JSON format file.
def python_dict_to_json_file(file_path):
try:
# Get a file object with write permission.
file_object = open(file_path, 'w')
dict_object = dict(name='Tom', age=25, score=100)
# Save dict data into the JSON file.
json.dump(dict_object, file_object)
print(file_path + " created. ")
except FileNotFoundError:
print(file_path + " not found. ")
if __name__ == '__main__':
python_dict_to_json_file("./teacher_data.json")
```
When you execute above code, you can find the teacher\_data.json file in current execution folder.
**2.2 Load JSON File Data To Python Dict.**
1. Create a python file object by open method.
2. Call json.load method to retrieve the JSON file content to a python dict object.
```python
import json
# Load JSON file string to python dict.
def python_json_file_to_dict(file_path):
try:
# Get a file object with write permission.
file_object = open(file_path, 'r')
# Load JSON file data to a python dict object.
dict_object = json.load(file_object)
print(dict_object)
except FileNotFoundError:
print(file_path + " not found. ")
if __name__ == '__main__':
python_json_file_to_dict("./teacher_data.json")
```
#### 3. Python Class Instance Serialize And Deserialize.
Besides serialize/deserialize Python dict object between JSON string or file. We can also dump / load any Python class instance between JSON string or file.[READ : How To Use User Defined Exception In Python](https://www.dev2qa.com/how-to-use-user-defined-exception-in-python/)
**3.1 Dump Python Class Instance To JSON String.**
1. Create a python class.
2. Add a method which can return a python dict object based on the class instance.
```python
# Convert Teacher class instance to a python dict object.
def teacher_to_dict(self, teacher):
dict_ret = dict(name=teacher.name, sex=teacher.sex, age=teacher.age)
return dict_ret
```
1. Call json.dumps(class\_instance, **default**=self.teacher\_to\_dict) method and set the convert method name in step 2 to parameter **default**. If do not set the default parameter value, it will throw **TypeError: Object of type ‘Teacher’ is not JSON serializable** error.
```python
json_string = json.dumps(self, default=self.teacher_to_dict)
```
**3.2 Load JSON String To Python Class Instance.**
1. Create a python class.
2. Add a method which can return a class instance from loaded python dict object.
```python
# Convert a dict object to a Teacher class instance.
def dict_to_teacher(self, dict):
name = dict['name']
sex = dict['sex']
age = dict['age']
ret = Teacher(name, sex, age)
return ret
```
1. Call json.loads(json\_string, **object\_hook**=self.dict\_to\_teacher) method and pass the method name in step 2 to the **object\_hook** parameter.
```python
teacher_object = json.loads(json_string, object_hook=self.dict_to_teacher)
```
**3.3 Dump Python Class Instance To JSON File.**
It is similar with steps in 3.1. The difference is you should call **json.dump(class\_instance, file\_object, default=self.teacher\_to\_dict)** method.
**3.4 Load JSON File String To Python Class Instance.**
It is similar with steps in 3.2. The difference is you should call **json.load(file\_object, object\_hook=self.dict\_to\_teacher)** method.
**3.5 Python Class Instance And JSON Conversion Example.**
```python
'''
Created on Aug 19, 2018
@author: zhaosong
'''
import json
# Define a python class.
class Teacher(object):
# This is the class initialization method.
def __init__(self, name, sex, age):
self.name = name
self.sex = sex
self.age = age
# Convert Teacher class instance to a python dict object.
def teacher_to_dict(self, teacher):
dict_ret = dict(name=teacher.name, sex=teacher.sex, age=teacher.age)
return dict_ret
# Convert a dict object to a Teacher class instance.
def dict_to_teacher(self, dict):
name = dict['name']
sex = dict['sex']
age = dict['age']
ret = Teacher(name, sex, age)
return ret
# Translate Teacher object to JSON string.
def teacher_object_to_json(self):
json_string = json.dumps(self, default=self.teacher_to_dict)
print(json_string)
return json_string
# Translate JSON string to Teacher object.
def json_string_to_teacher_object(self, json_string):
teacher_object = json.loads(json_string, object_hook=self.dict_to_teacher)
print(teacher_object.name)
print(teacher_object.sex)
print(teacher_object.age)
return teacher_object
# This method will save Teacher instance data as a JSON string into a file.
def save_teacher_json_to_file(self, file_path):
try:
file_object = open(file_path, 'w')
json.dump(self, file_object, default=self.teacher_to_dict)
print("Teacher object has been saved in file " + file_path)
except FileNotFoundError:
print(file_path + " not found.")
# This method will load a JSON string from file and return a Teacher class instance.
def load_teacher_json_from_file(self, file_path):
try:
file_object = open(file_path)
teacher_object = json.load(file_object, object_hook=self.dict_to_teacher)
print("name : " + teacher_object.name)
print("sex : " + teacher_object.sex)
print("age : " + str(teacher_object.age))
except FileNotFoundError:
print(file_path + " not found.")
if __name__ == '__main__':
# Convert custom python class instance to JSON string.
teacher = Teacher('Jerry', 'Male', 26)
print(json.dumps(teacher, default=teacher.teacher_to_dict))
# Convert JSON string to custom python class instance.
teacher_json_string = '{"name":"Jerry", "sex":"Male", "age":25}'
teacher = Teacher('','',1)
teacher.json_string_to_teacher_object(teacher_json_string)
teacher = Teacher('Tom', 'Male', 25)
# Save teacher object to JSON file.
teacher.save_teacher_json_to_file('./teacher.json')
# Load teach data from JSON file and return a teacher instance.
teacher.load_teacher_json_from_file("./teacher.json")
```
Reference :