JSON in Python — requests, pandas, FastAPI & Data Pipelines

1import json
2from datetime import datetime, date
3from decimal import Decimal
4from uuid import UUID
5
6class CustomEncoder(json.JSONEncoder):
7    def default(self, obj):
8        if isinstance(obj, (datetime, date)):
9            return obj.isoformat()
10        if isinstance(obj, Decimal):
11            return float(obj)
12        if isinstance(obj, UUID):
13            return str(obj)
14        if isinstance(obj, set):
15            return list(obj)
16        return super().default(obj)
17
18order = {
19    "id": UUID("12345678-1234-5678-1234-567812345678"),
20    "total": Decimal("49.99"),
21    "placed_at": datetime(2026, 4, 2, 14, 30),
22    "tags": {"express", "priority"},
23}
24
25print(json.dumps(order, cls=CustomEncoder, indent=2))
26# {
27#   "id": "12345678-1234-5678-1234-567812345678",
28#   "total": 49.99,
29#   "placed_at": "2026-04-02T14:30:00",
30#   "tags": ["express", "priority"]
31# }

1import requests
2
3# GET — parse JSON response
4response = requests.get("https://api.github.com/users/octocat")
5response.raise_for_status()
6user = response.json()  # Automatically parses JSON
7print(user["login"])     # "octocat"
8
9# POST — send JSON body
10new_post = {"title": "Hello", "body": "World", "userId": 1}
11response = requests.post(
12    "https://jsonplaceholder.typicode.com/posts",
13    json=new_post,  # Sets Content-Type: application/json automatically
14)
15created = response.json()
16print(created["id"])  # 101

1import requests
2
3def fetch_user(user_id: int) -> dict:
4    try:
5        response = requests.get(
6            f"https://api.example.com/users/{user_id}",
7            timeout=10,
8        )
9        response.raise_for_status()
10        return response.json()
11    except requests.exceptions.HTTPError as e:
12        print(f"HTTP error: {e.response.status_code}")
13        raise
14    except requests.exceptions.JSONDecodeError:
15        print("Response was not valid JSON")
16        raise
17    except requests.exceptions.ConnectionError:
18        print("Could not connect to API")
19        raise

1from fastapi import FastAPI, HTTPException
2from pydantic import BaseModel, EmailStr, Field
3from datetime import datetime
4
5app = FastAPI()
6
7class UserCreate(BaseModel):
8    name: str = Field(min_length=1, max_length=100)
9    email: EmailStr
10    age: int = Field(ge=0, le=150)
11    role: str = Field(default="viewer", pattern="^(admin|editor|viewer)$")
12
13class UserResponse(BaseModel):
14    id: int
15    name: str
16    email: str
17    role: str
18    created_at: datetime
19
20    class Config:
21        from_attributes = True
22
23@app.post("/users", response_model=UserResponse, status_code=201)
24async def create_user(user: UserCreate):
25    # Pydantic already validated the JSON body
26    db_user = await db.create(user.model_dump())
27    return UserResponse.model_validate(db_user)
28
29@app.get("/users/{user_id}", response_model=UserResponse)
30async def get_user(user_id: int):
31    user = await db.get(user_id)
32    if not user:
33        raise HTTPException(status_code=404, detail="User not found")
34    return UserResponse.model_validate(user)

1# Pretty-print a JSON file
2python -m json.tool data.json
3
4# Pretty-print from stdin (piped from curl)
5curl -s https://api.github.com/users/octocat | python -m json.tool
6
7# Compact/minify JSON
8python -c "import json,sys; json.dump(json.load(sys.stdin), sys.stdout, separators=(',',':'))" < data.json
9
10# Extract a field with Python one-liner
11echo '{"name":"Alice","age":30}' | python -c "import json,sys; print(json.load(sys.stdin)['name'])"