The Two Core Types: date and datetime
The datetime module gives you four things worth knowing: date, time, datetime, and timedelta. The first three are what they sound like; the fourth is a span of time.
A date represents a day — year, month, day — with no clock attached. A datetime is a date plus a time. If you don't need the clock, date is the tidier choice.
Creating Specific Dates
Construct directly:
Arguments are year, month, day for date, and up to year, month, day, hour, minute, second, microsecond for datetime.
Reading Fields
Every date/datetime has attributes:
isoformat() is your friend for machine-readable output — it produces something like "2026-04-20T09:30:15" that other systems can parse unambiguously.
Formatting With strftime
For human-readable output, .strftime(fmt) turns a date or datetime into a formatted string:
The format codes most often worth remembering:
%Y— 4-digit year (2026)%m— month number, zero-padded (04)%d— day of month, zero-padded (20)%H/%I— hour, 24/12 hour format%M— minute%S— second%A/%a— weekday name full / abbreviated (Monday / Mon)%B/%b— month name full / abbreviated (April / Apr)%p— AM/PM
You don't need to memorize them; bookmark a reference and look them up when you need one.
Parsing With strptime
The reverse direction: take a string with a known shape and turn it into a datetime:
The format string must match the input exactly. If it doesn't, strptime raises ValueError.
For ISO-8601 strings (the machine-readable standard), there's a simpler shortcut in modern Python:
If you're dealing with random formats, the external dateutil package (pip install python-dateutil) has a forgiving parser.parse() that takes a reasonable guess.
Arithmetic With timedelta
To do math on dates, use timedelta for the difference or offset:
timedelta arguments: days, seconds, microseconds, milliseconds, minutes, hours, weeks. No months or years — months are variable length. For month/year math, use dateutil.relativedelta:
from dateutil.relativedelta import relativedelta
from datetime import date
today = date.today()
next_quarter = today + relativedelta(months=3)
print(next_quarter)
Timezones: Naive vs Aware
A datetime without timezone info is naive — Python doesn't know what timezone it represents. Time math on naive datetimes is fine as long as you stay within one logical timezone; the trouble starts the moment data from different zones meets.
An aware datetime carries timezone info with it. Attach a timezone explicitly:
Python 3.9 added the zoneinfo module for named timezones (using the system's IANA database):
Convert between zones with .astimezone():
A rule worth committing to memory: store datetimes in UTC, convert to local zones only at display time. That one habit prevents most timezone bugs.
Timestamps
A Unix timestamp is the number of seconds since 1970-01-01 UTC. Python converts easily:
Timestamps are useful for comparisons, sorting, and interop with other systems. For human-facing output, convert back to a datetime first.
Measuring How Long Something Takes
For quick timings, subtract two datetimes:
For more serious performance measurement, use time.perf_counter() — it has sub-microsecond resolution and is immune to system clock changes. datetime.now() is fine for "how long did this API call take" style numbers.
Patterns You'll Reuse
What to Take Away
date,datetime, andtimedeltacover 90% of needs.- Use ISO-8601 for machine-readable;
strftimefor human-readable. - Store in UTC; convert at display time.
- Use
zoneinfofor named timezones. - For months and years, reach for
dateutil.relativedelta.
One more tool for your real-world toolkit: regular expressions, up next.
Frequently Asked Questions
How do I get the current date and time in Python?
datetime.now() returns the current local date-and-time. datetime.utcnow() returns UTC (though the modern preference is datetime.now(timezone.utc) since utcnow() returns a naive datetime). For just the date, use date.today().
How do I format a date as a string?
Use .strftime(format) with format codes like %Y-%m-%d for year-month-day. Example: datetime.now().strftime('%Y-%m-%d %H:%M'). To parse a string back, use datetime.strptime(text, format) with the same format codes.
How do I add days to a date in Python?
Use timedelta: from datetime import date, timedelta; date.today() + timedelta(days=7). timedelta supports days, hours, minutes, seconds, weeks, and more. For month and year math, use the external dateutil.relativedelta — timedelta doesn't know about months.
