Python Forum
Append JSON's and write to file
Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Append JSON's and write to file
#1
I have a Sample JSON record in a file as below
{ "name":"John", "age":30, "car":"BMW" }

I want to create more JSON records out of it and i want to minimize the i/o by not writing to the file system everytime i create sample record, the code below is to change the age using parameters and hold the JSON records in a list and write to the file system when i am done generating the records.


    # Read the sample file
    with open("C:/myfile.json") as file:
        originalJSON = json.load(file)
    # How many sample Records?
    numberOfRecords = 4
    i = 1
    myOutput = [] # initializing a dummy list to append my json's
    while (i <= numberOfRecords):
            # Change the age
            originalJSON["age"] = i
            myOutput.append(originalJSON)
            i += 1
    # After appending all the JSON's to the list i want to write the JSON array to a file
    with open("C:/multiplerecords.json", 'w') as multipleJsons:
        json.dump(myOutput, multipleJsons)
The output looks like

[{ "name":"John", "age":4, "car":"BMW" }
{ "name":"John", "age":4, "car":"BMW" }
{ "name":"John", "age":4, "car":"BMW" }
{ "name":"John", "age":4, "car":"BMW" }]

$$$ the issue i see is, when i write myOutput list it generates 4 records in it but all of them are duplicates, the last json that was produced is written to the whole list. Instead i am looking for something like below

[{ "name":"John", "age":1, "car":"BMW" }
{ "name":"John", "age":2, "car":"BMW" }
{ "name":"John", "age":3, "car":"BMW" }
{ "name":"John", "age":4, "car":"BMW" }]


###################################################################################################################
Reply
#2
originalJSON is a python object.

On line 10 you modify the object. On line 11, you append the object to your list. But none of these operations makes a copy. All 4 items in the list are the same object.

Probably you want to make a copy of it at the time you append.
        myOutput.append(copy.copy(originalJSON))
Reply
#3
Thank you for the reply
is copy.copy a valid command? I tried it and python spit out an error.
Reply
#4
Generally if you see a command in two parts like that, it indicates that it's part of a library. It's a standard library in this case, but you'll still need to import it.

import copy
within your script.

https://docs.python.org/3/library/copy.html
Reply
#5
Thank you for that explanation, it really helped. I ended up using the deep copy function.
Appreciate your help.
Reply


Possibly Related Threads…
Thread Author Replies Views Last Post
  How do I write a single 8-bit byte to a file? MysticLord 2 298 Sep-03-2020, 12:27 PM
Last Post: MysticLord
  How to convert what appears to be a JSON file to CSV NewBeie 4 339 Aug-28-2020, 04:45 PM
Last Post: Larz60+
  live updated json file Nyanpasu 2 354 Aug-22-2020, 04:41 PM
Last Post: Nyanpasu
  unable to write to log file Mekala 2 321 Aug-12-2020, 11:02 PM
Last Post: Mekala
  List Won't Write in Text File IILawrenceII 4 398 Jul-17-2020, 11:16 PM
Last Post: j.crater
  Process Data from one csv file and write to another CSV file specific column ajin9581 1 371 Jun-17-2020, 06:00 PM
Last Post: buran
  empty json file error mcmxl22 1 640 Jun-17-2020, 10:20 AM
Last Post: buran
  saving a dictionary as json file vinay_py 6 414 Jun-06-2020, 05:07 PM
Last Post: vinay_py
  How to append a tuple full of records to a dbf file in Python? DarkCoder2020 4 577 May-29-2020, 02:40 PM
Last Post: DarkCoder2020
  Write SQLite query result to file hjk6734 1 349 May-27-2020, 12:17 PM
Last Post: menator01

Forum Jump:

User Panel Messages

Announcements
Announcement #1 8/1/2020
Announcement #2 8/2/2020
Announcement #3 8/6/2020