Python — Dates

The datetime module

from datetime import datetime, date, time, timedelta

now = datetime.now()          # 2026-08-23 21:14:07.123456
today = date.today()          # 2026-08-23
noon = time(12, 0)            # 12:00:00

Building specific moments

launch = datetime(2026, 12, 31, 23, 59)
launch.year      # 2026
launch.month     # 12
launch.hour      # 23

Argument order is fixed: (year, month, day[, hour, minute, second]) — no zero-month trap like JavaScript.

Formatting — strftime

now.strftime("%Y-%m-%d")           # "2026-08-23"
now.strftime("%d/%m/%Y %H:%M")     # "23/08/2026 21:14"
now.strftime("%A, %B %d")          # "Sunday, August 23"

# locale-friendly:
now.strftime("%x %X")

Code	Meaning
%Y / %y	4-digit / 2-digit year
%m / %d	month / day (zero-padded)
%H:%M:%S	24h time
%A / %B	weekday / month names

Parsing strings → datetime — strptime

datetime.strptime("23/08/2026", "%d/%m/%Y")
# datetime(2026, 8, 23, 0, 0)

Format string MUST match the input exactly or ValueError. (f = format out, p = parse in.)

Math with timedelta

later = now + timedelta(days=30, hours=2)
ago = now - timedelta(weeks=1)

diff = later - now
diff.days        # 30
diff.total_seconds()

Date arithmetic "just works" across month/year boundaries.

Comparisons

deadline = datetime(2026, 9, 1)
now < deadline          # True — plain comparison operators

Timezones — the honest warning

Naive datetimes (no zone info) cause real production bugs:

from datetime import timezone

aware = datetime.now(timezone.utc)         # UTC-aware ✓
aware.tzinfo                               # not None

local = aware.astimezone()                 # convert to local zone

Rule: store UTC, convert at display. For serious zone work use the zoneinfo module (stdlib) or pytz.

Timestamps

now.timestamp()                    # float seconds since epoch
datetime.fromtimestamp(1790000000)

Handy for measuring elapsed time; time.perf_counter() is better for pure durations.

Mini Practice

1. Print today as YYYY-MM-DD and "Sunday, August 23" forms.
2. Days until New Year via subtraction.
3. Parse three user-entered date formats with strptime.
4. Add 90 days to today; print weekday name.
5. Build a naive vs aware UTC datetime pair; compare printing.

Next: math → (Python flavor)