Handle JSON Date Strings in Python with datetime

JSON Dates to Python datetime

JSON has no native date type. Dates are transmitted as strings, typically in ISO 8601 format. Python's datetime module provides proper date/time handling.

Example JSON

{
  "id": 42,
  "title": "Deploy v2.0",
  "created_at": "2024-06-15T09:30:00Z",
  "updated_at": "2024-06-15T14:22:33+09:00",
  "due_date": "2024-07-01"
}

Generated Python (Dataclass)

from dataclasses import dataclass
from datetime import datetime, date

@dataclass
class Task:
    id: int
    title: str
    created_at: datetime
    updated_at: datetime
    due_date: date

Parsing ISO 8601 Strings

from datetime import datetime, date

# Full datetime with timezone
dt = datetime.fromisoformat("2024-06-15T09:30:00Z")
# Python 3.11+: handles "Z" suffix
# Python < 3.11: replace "Z" with "+00:00"

# Date only
d = date.fromisoformat("2024-07-01")

Deserialization with Post-Processing

json.loads() returns strings, not datetime objects. You need a conversion step:

import json

data = json.loads(raw_json)
task = Task(
    id=data["id"],
    title=data["title"],
    created_at=datetime.fromisoformat(data["created_at"]),
    updated_at=datetime.fromisoformat(data["updated_at"]),
    due_date=date.fromisoformat(data["due_date"]),
)

With Pydantic (Automatic)

Pydantic handles datetime parsing automatically:

from pydantic import BaseModel
from datetime import datetime, date

class Task(BaseModel):
    id: int
    title: str
    created_at: datetime
    updated_at: datetime
    due_date: date

task = Task.model_validate_json(raw_json)
# created_at is already a datetime object!

Timezone Awareness

Always work with timezone-aware datetimes:

from datetime import timezone

utc_now = datetime.now(timezone.utc)

Nullable Timestamps

For fields that may be null (e.g., deleted_at):

from typing import Optional
from datetime import datetime

deleted_at: Optional[datetime] = None