Python read JSON file and modify

Question

Hi I am trying to take the data from a json file and insert and id then perform POST REST  my file data json has          name   myname      and I would like to add an id so that the json data looks like            id   134        name    myname       So I tried   import json f   open  data json   r   data   f read   jsonObj   json loads data    I can t get to load the json format file   What should I do so that I can convert the json file into json object and add another id value

User · Answer

I would like to present a modified version of Vadim's solution. It helps to deal with asynchronous requests to write/modify json file. I know it wasn't a part of the original question but might be helpful for others.

In case of asynchronous file modification os.remove(filename) will raise FileNotFoundError if requests emerge frequently. To overcome this problem you can create temporary file with modified content and then rename it simultaneously replacing old version. This solution works fine both for synchronous and asynchronous cases.

import os, json, uuid

filename = 'data.json'
with open(filename, 'r') as f:
    data = json.load(f)
    data['id'] = 134 # <--- add `id` value.
    # add, remove, modify content

# create randomly named temporary file to avoid 
# interference with other thread/asynchronous request
tempfile = os.path.join(os.path.dirname(filename), str(uuid.uuid4()))
with open(tempfile, 'w') as f:
    json.dump(data, f, indent=4)

# rename temporary file replacing old file
os.rename(tempfile, filename)

User · Answer

Set item using data  id           import json  with open  data json    r    as f      data   json load f      data  id     134    lt --- add  id  value      f seek 0            lt --- should reset file position to the beginning      json dump data  f  indent 4      f truncate         remove remaining part

User · Answer

falsetru s solution is nice  but has a little bug   Suppose original  id  length was larger than 5 characters  When we then dump with the new  id   134 with only 3 characters  the length of the string being written from position 0 in file is shorter than the original length  Extra chars  such as      left in file from the original content   I solved that by replacing the original file   import json import os  filename    data json  with open filename   r   as f      data   json load f      data  id     134    lt --- add  id  value   os remove filename  with open filename   w   as f      json dump data  f  indent 4

User · Answer

try this script   with open  data json   as f      data   json load f      data  id     134     json dump data  open  data json    w    indent   4    the result is          name   mynamme        id  134     Just the arrangement is different  You can solve the problem by converting the  data  type to a list  then arranging it as you wish  then returning it and saving the file  like that   index add   0 with open  data json   as f      data   json load f      data li     k  v  for k  v in data items        data li insert index add    id   134       data    data li i  0  data li i  1  for i in range 0  len data li        json dump data  open  data json    w    indent   4    the result is          id  134       name   myname      you can add if condition in order not to repeat the key  just change it  like that   index add   0 n k    id  n v   134 with open  data json   as f      data   json load f      if n k in data          data n k    n v     else         data li     k  v  for k  v in data items           data li insert index add   n k  n v          data    data li i  0  data li i  1  for i in range 0  len data li        json dump data  open  data json    w    indent   4

User · Answer

There is really quite a number of ways to do this and all of the above are in one way or another valid approaches    Let me add a straightforward proposition  So assuming your current existing json file looks is this              name   myname      And you want to bring in this new json content  adding key  id            id    134         name    myname       My approach has always been to keep the code extremely readable with easily traceable logic  So first  we read the entire existing json file into memory  assuming you are very well aware of your json s existing key s     import json     first  get the absolute path to json file PATH TO JSON    data json     assuming same directory  but you can work your magic here with os      read existing json to memory  you do this to preserve whatever existing data   with open PATH TO JSON  r   as jsonfile      json content   json load jsonfile    this is now in memory  you can use it outside  open    Next  we use the  with open    syntax again  with the  w  option   w  is a write mode which lets us edit and write new information to the file  Here s the catch that works for us     any existing json with the same target write name will be erased automatically    So what we can do now  is simply write to the same filename with the new data    add the id key-value pair  rmbr that it already has the  name  key value  json content  id      134   with open PATH TO JSON  w   as jsonfile      json dump json content  jsonfile  indent 4    you decide the indentation level   And there you go  data json should be good to go for an good old POST request

[python] Python read JSON file and modify

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