Datetime, Timezones (zoneinfo) & ISO 8601

1. The Core Temporal Classes

The standard datetime module exposes four primary classes:

• date: Calendar date (year, month, day).
• time: Time of day independent of date (hour, minute, second, microsecond).
• datetime: Combination of date and time.
• timedelta: A duration expressing the exact difference between two dates or times.

from datetime import datetime, date, timedelta

# Create specific date and time
launch_date = datetime(2026, 12, 1, 9, 30, 0)
print("Launch Day of Week:", launch_date.strftime("%A"))  # Tuesday

# Timedelta Arithmetic (Add 14 days and 6 hours)
maintenance_window = launch_date + timedelta(days=14, hours=6)
print("Maintenance Scheduled:", maintenance_window)

2. Naive vs Aware Datetimes: Modern Timezones with zoneinfo

A naive datetime holds no timezone context (e.g., "2026-10-15 14:00"—in what city?). An aware datetime explicitly tracks its UTC offset and daylight saving status using zoneinfo.ZoneInfo:

from datetime import datetime, timezone
from zoneinfo import ZoneInfo

# 1. ALWAYS create current timestamps in UTC
utc_now = datetime.now(timezone.utc)
print("UTC Timestamp:", utc_now.isoformat())

# 2. Convert UTC to local regional timezones cleanly
tokyo_time = utc_now.astimezone(ZoneInfo("Asia/Tokyo"))
ny_time = utc_now.astimezone(ZoneInfo("America/New_York"))
delhi_time = utc_now.astimezone(ZoneInfo("Asia/Kolkata"))

print("Tokyo Local:", tokyo_time.strftime("%Y-%m-%d %H:%M:%S %Z"))
print("New York Local:", ny_time.strftime("%Y-%m-%d %H:%M:%S %Z"))
print("New Delhi Local:", delhi_time.strftime("%Y-%m-%d %H:%M:%S %Z"))

3. High-Performance ISO 8601 & Formatting

Modern web APIs exchange timestamps adhering to the ISO 8601 standard (e.g. 2026-10-15T14:30:00Z). Python provides optimized C-level parsing with fromisoformat():

# Parsing ISO 8601 strings directly (Fast & Robust)
raw_api_string = "2026-10-15T18:45:30.125000+00:00"
parsed_dt = datetime.fromisoformat(raw_api_string)

# Calculate elapsed time since API event
elapsed = datetime.now(timezone.utc) - parsed_dt
print(f"Elapsed time: {elapsed.total_seconds():.1f} seconds ago")

# Custom String Formatting with strftime
formatted = parsed_dt.strftime("%d %B %Y at %I:%M %p")
print("Readable Display:", formatted)