JSON Handling

what JSON is

JSON (JavaScript Object Notation) is the standard format for data exchange. It looks like Python dictionaries and lists:

{
  "name": "Alice",
  "age": 30,
  "hobbies": ["reading", "coding"],
  "address": {
    "city": "NYC",
    "zip": "10001"
  }
}

the json module

import json

# Parse JSON string → Python dict
data = json.loads('{"name": "Alice", "age": 30}')
print(data["name"])  # "Alice"

# Convert Python → JSON string
json_str = json.dumps({"name": "Bob", "age": 25})
print(json_str)  # '{"name": "Bob", "age": 25}'

# Pretty print
json.dumps(data, indent=2)

json files

# Read JSON file
with open("data.json") as f:
    data = json.load(f)  # Note: load, not loads

# Write JSON file
with open("output.json", "w") as f:
    json.dump(data, f, indent=2)  # Note: dump, not dumps

nested access

data = {
    "users": [
        {"name": "Alice", "scores": [95, 82, 91]},
        {"name": "Bob", "scores": [88, 79, 94]}
    ]
}

# Access nested data
first_user = data["users"][0]["name"]  # "Alice"
first_score = data["users"][0]["scores"][0]  # 95

json to DataFrame

import pandas as pd

# List of dicts → DataFrame
json_list = [
    {"name": "Alice", "age": 30},
    {"name": "Bob", "age": 25}
]
df = pd.DataFrame(json_list)

# Nested JSON → normalize
pd.json_normalize(data, record_path="users")