python.naive_datetime

Correctness Medium

Detects datetime.now() without timezone or datetime.utcnow() usage, which creates naive datetime objects.

Why It Matters

Naive datetimes (those without timezone info) cause subtle bugs:

• Server location matters — Code behaves differently depending on where it runs
• Daylight saving bugs — Times shift unexpectedly twice a year
• Data corruption — Timestamps become ambiguous when stored and retrieved
• Distributed system chaos — Different services interpret the same timestamp differently

UTC awareness is essential for any system with multiple servers, users in different timezones, or data that persists.

Example

# ❌ Before
from datetime import datetime

now = datetime.now()  # What timezone? Depends on server.

# ✅ After
from datetime import datetime, timezone

now = datetime.now(tz=timezone.utc)

Always use UTC for storage and computation. Convert to local time only for display.

What Unfault Detects

• datetime.now() without tz parameter
• datetime.utcnow() (deprecated, returns naive datetime)
• datetime.today() (naive datetime)

Auto-Fix

Unfault adds tz=timezone.utc to datetime.now() calls and converts utcnow() to now(tz=timezone.utc).

Common Patterns

# ✅ Use timezone-aware datetimes
from datetime import datetime, timezone

# Current time in UTC
now = datetime.now(tz=timezone.utc)

# Parse ISO format (Python 3.11+)
dt = datetime.fromisoformat("2024-01-15T10:30:00+00:00")

# Store as ISO format
timestamp = now.isoformat()