32_json_tutorial.py

# Working with JSON in Python

import json

# ========== CONVERTING PYTHON → JSON ==========

# 1. dict → JSON string (serialization)
data = {
    "name": "Pavel",
    "age": 25,
    "city": "Moscow",
    "is_student": False,
    "grades": [85, 90, 92]
}

json_string = json.dumps(data)
print(f"JSON string: {json_string}")

# 2. With formatting (pretty)
json_string = json.dumps(data, indent=4, ensure_ascii=False)
print(f"Formatted JSON:\n{json_string}")

# 3. Writing to file
with open('data.json', 'w', encoding='utf-8') as file:
    json.dump(data, file, indent=4, ensure_ascii=False)

# ========== CONVERTING JSON → PYTHON ==========

# 4. JSON string → dict (deserialization)
json_string = '{"name": "Pavel", "age": 25, "city": "Moscow"}'
data = json.loads(json_string)
print(f"Python object: {data}")
print(f"Name: {data['name']}")

# 5. Reading from file
with open('data.json', 'r', encoding='utf-8') as file:
    data = json.load(file)
    print(f"From file: {data}")

# ========== JSON ⟷ PYTHON DATA TYPES ==========

# JSON → Python:
# object → dict
# array → list
# string → str
# number (int) → int
# number (real) → float
# true/false → True/False
# null → None

# 6. Example of all types
json_data = '''
{
    "string": "text",
    "number_int": 42,
    "number_float": 3.14,
    "boolean": true,
    "null_value": null,
    "array": [1, 2, 3],
    "object": {"key": "value"}
}
'''

data = json.loads(json_data)
print(data)

# ========== WORKING WITH COMPLEX OBJECTS ==========

# 7. Nested structures
complex_data = {
    "user": {
        "name": "Pavel",
        "contacts": {
            "email": "pavel@example.com",
            "phone": "+7 123 456 7890"
        }
    },
    "posts": [
        {"id": 1, "title": "First post"},
        {"id": 2, "title": "Second post"}
    ]
}

# Accessing nested data
print(complex_data["user"]["contacts"]["email"])
print(complex_data["posts"][0]["title"])

# ========== ERROR HANDLING ==========

# 8. Handling invalid JSON
invalid_json = '{"name": "Pavel", "age": 25,}'  # Extra comma

try:
    data = json.loads(invalid_json)
except json.JSONDecodeError as e:
    print(f"JSON parsing error: {e}")

# ========== CUSTOM SERIALIZATION ==========

# 9. Serializing classes (doesn't work by default)
from datetime import datetime

class Person:
    def __init__(self, name, age, birthday):
        self.name = name
        self.age = age
        self.birthday = birthday

person = Person("Pavel", 25, datetime(2001, 1, 15))

# Error:
# json.dumps(person)  # TypeError: Object of type Person is not JSON serializable

# 10. Custom encoder
class PersonEncoder(json.JSONEncoder):
    def default(self, obj):
        if isinstance(obj, Person):
            return {
                "name": obj.name,
                "age": obj.age,
                "birthday": obj.birthday.isoformat()
            }
        if isinstance(obj, datetime):
            return obj.isoformat()
        return super().default(obj)

json_string = json.dumps(person, cls=PersonEncoder, indent=4)
print(f"Custom serialization:\n{json_string}")

# 11. Alternative: function for serialization
def serialize_person(obj):
    if isinstance(obj, Person):
        return {
            "name": obj.name,
            "age": obj.age,
            "birthday": obj.birthday.isoformat()
        }
    raise TypeError(f"Type {type(obj)} is not serializable")

json_string = json.dumps(person, default=serialize_person, indent=4)
print(json_string)

# ========== PRACTICAL EXAMPLES ==========

# 12. Loading configuration
config = {
    "database": {
        "host": "localhost",
        "port": 5432,
        "name": "mydb"
    },
    "debug": True
}

with open('config.json', 'w') as file:
    json.dump(config, file, indent=4)

with open('config.json', 'r') as file:
    loaded_config = json.load(file)
    print(f"Database host: {loaded_config['database']['host']}")

# 13. API response
api_response = '''
{
    "status": "success",
    "data": {
        "users": [
            {"id": 1, "name": "Alice"},
            {"id": 2, "name": "Bob"}
        ]
    }
}
'''

response = json.loads(api_response)
for user in response["data"]["users"]:
    print(f"ID: {user['id']}, Name: {user['name']}")

# ========== DUMPS/DUMP PARAMETERS ==========

# indent - indentation for formatting
# ensure_ascii - False for unicode support
# sort_keys - sort keys
# separators - separators (compact: (',', ':'))

data = {"b": 2, "a": 1, "c": 3}

compact = json.dumps(data, separators=(',', ':'))
print(f"Compact: {compact}")

sorted_json = json.dumps(data, sort_keys=True, indent=2)
print(f"Sorted:\n{sorted_json}")