Extract part of data from JSON file with python [duplicate]

Question

I have been trying to extract only certain data from a JSON file. I managed to decode the JSON and get the wanted data into a python dict. When I print out the dict it shows all the wanted data, but when I try to write the dict into a new file, only the last object gets written. One thing that I can't understand is also why when I print the dict I get multiple dicts objects instead of 1 as I would expect.

My code:

import json
input_file=open('json.json', 'r')
output_file=open('test.json', 'w')
json_decode=json.load(input_file)
for item in json_decode:
    my_dict={}
    my_dict['title']=item.get('labels').get('en').get('value')
    my_dict['description']=item.get('descriptions').get('en').get('value')
    my_dict['id']=item.get('id')
    print my_dict
back_json=json.dumps(my_dict, output_file)
output_file.write(back_json)
output_file.close() 

my json.json file:

[
{"type":"item","labels":{"en":{"language":"en","value":"George Washington"}},"descriptions":{"en":{"language":"en","value":"American politician, 1st president of the United States (in office from 1789 to 1797)"}},"id":"Q23"},
{"type":"item","aliases":{"en":[{"language":"en","value":"Douglas Noël Adams"},{"language":"en","value":"Douglas Noel Adams"}]},"labels":{"en":{"language":"en","value":"Douglas Adams"}},"descriptions":{"en":{"language":"en","value":"English writer and humorist"}},"id":"Q42"},
{"type":"item","aliases":{"en":[{"language":"en","value":"George Bush"},{"language":"en","value":"George Walker Bush"}]},"labels":{"en":{"language":"en","value":"George W. Bush"}},"descriptions":{"en":{"language":"en","value":"American politician, 43rd president of the United States from 2001 to 2009"}},"id":"Q207"},
{"type":"item","aliases":{"en":[{"language":"en","value":"Velázquez"},{"language":"en","value":"Diego Rodríguez de Silva y Velázquez"}]},"labels":{"en":{"language":"en","value":"Diego Velázquez"}},"descriptions":{"en":{"language":"en","value":"Spanish painter who was the leading artist in the court of King Philip IV"}},"id":"Q297"},
{"type":"item","labels":{"en":{"language":"en","value":"Eduardo Frei Ruiz-Tagle"}},"descriptions":{"en":{"language":"en","value":"Chilean politician and former President"}},"id":"Q326"}
]

print my_dict output:

{'id': u'Q23', 'description': u'American politician, 1st president of the United States (in office from 1789 to 1797)', 'title': u'George Washington'}
{'id': u'Q42', 'description': u'English writer and humorist', 'title': u'Douglas Adams'}
{'id': u'Q207', 'description': u'American politician, 43rd president of the United States from 2001 to 2009', 'title': u'George W. Bush'}
{'id': u'Q297', 'description': u'Spanish painter who was the leading artist in the court of King Philip IV', 'title': u'Diego Vel\xe1zquez'}
{'id': u'Q326', 'description': u'Chilean politician and former President', 'title': u'Eduardo Frei Ruiz-Tagle'}

output in the file test.json:

{"id": "Q326", "description": "Chilean politician and former President", "title": "Eduardo Frei Ruiz-Tagle"}

Also I would like to know why the dict is outputing 'title': u'Diego Vel\xe1zquez' but if i go print my_dict.values()[2] i Get the name written normaly as Diego Velázquez.

Many thanks

Answer 1

Your code creates new dictionary object for each object with:

my_dict={}

Moreover, it overwrites the previous contents of the variable. Old dictionary in m_dict is deleted from memory.

Try to create a list before your for loop and store the result there.

result = []
for item in json_decode:
    my_dict={}
    my_dict['title']=item.get('labels').get('en').get('value')
    my_dict['description']=item.get('descriptions').get('en').get('value')
    my_dict['id']=item.get('id')
    print(my_dict)
    result.append(my_dict)

Finally, write the result to the output:

back_json=json.dumps(result)

Printing the dictionary object aims to help the developer by showing the type of the data. In u'Diego Vel\xe1zquez', u at the start indicates a Unicode object (string). When object using is printed, it is decoded according to current language settings in your OS.

Answer 2

When you do this:

for item in json_decode:

You are looping through each line in the file.

Every time through the loop you are overriding the my_dict variable, which is why you get only one line in your output.

Once you load in the file, you can simply print out the json_decode variable to do what you want.

https://docs.python.org/3.3/library/json.html