How to get equivalent file size of a json object in Python?-CodePudding

I am writing a python object with json.dump. But I want to only write if the file size is less than 10KB.

How can estimate the size of an object before writing?

CodePudding user response：

Convert the JSON to a string, then use sys.getsizeof(). It returns the size in bytes, so you can divide by 1024 if you want to compare it to a threshold value in kilobytes.

sys.getsizeof(json.dumps(object))

Sample usage:

import json
import sys
x = '{"name":"John", "age":30, "car":null}'
y = json.loads(x)
print(sys.getsizeof(json.dumps(y))) # 89

Edit:
As mentioned in this thread, objects have a higher size in memory. So subtract 49 from the size to get a better estimate.

print(sys.getsizeof(json.dumps(y)) - 49)

CodePudding user response：

len(json.dumps(object)) is the answer after testing it.

I used the code below on an existing JSON file, which is 69961 bytes in size according to my file browser, and the code below.

sys.getsizeof() returns a higher number than the actual size of the resulting file at the end...

import json
import sys
import os

with open("somejson.json") as infile:
    data = json.load(infile)


print(len(json.dumps(data)))
print(sys.getsizeof(json.dumps(data)))

with open("somejson.json", "w") as outfile:
    json.dump(data, outfile)

print(os.path.getsize("somejson.json"))

output

69961
70010
69961