How to append a dictionary to a json file in Python?

Question

I want to read a json file in Python and add content to the file respecting the json format, but I can't manage to do it.

The json file "paises.json":

 {
  "España": [
    {
      "Superficie": 505944,
      "Población": 47450795
    }
  ],
  "Francia": [
    {
      "Superficie": 675417,
      "Población": 67407241
    }
  ]
}

I want to read that file in Python and append new content to it. The code is:

import json

with open("paises.json", "r", encoding="utf-8") as paises:
    datos = json.load(paises)
print(datos.keys())  # Show dictionary

nombre_pais = input("\nIndique el nombre del país\n")
nueva_superficie = float(input("\nIndique la superficie\n"))
nueva_poblacion = int(input("\nIndique la Población\n"))
nuevo_contenido = {nombre_pais: {"Superficie": nueva_superficie, "Población": nueva_poblacion}}

datos.update(nuevo_contenido)
print(datos)  # Show dictionary with new content

with open("paises.json", "a", encoding="utf-8") as paises:
    json.dump(nuevo_contenido, paises)

The result is not what I have expected:

{
  "España": [
    {
      "Superficie": 505944,
      "Población": 47450795
    }
  ],
  "Francia": [
    {
      "Superficie": 675417,
      "Población": 67407241
    }
  ]
}
{"Portugal": {"Superficie":  92090, "Poblaci\u00f3n":   10295909}}

The formatting is not correct, a comma and a square bracket are missing and the coding of the accents is not ok.

What can I do to correct it?

Thank you

Answer 1

You can't append new data directly to JSON file because it creates incorrect JSON.
(Exception can be when you want to create multi-JSON file)

With normal JSON you have to:

• read all data from file to memory,
• append new values in memory,
• write back all data ( datos ) from memory to file in "write mode" , not "append mode" .

with open("paises.json", "w", encoding="utf-8") as paises:
    json.dump(datos, paises)