Python Datetime Module Overview

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Overview of Python’s datetime Module

Python’s datetime module provides classes for manipulating dates, times, and timestamps. It’s in the standard library, so no installation is needed. Key classes include:

date: Handles dates (year, month, day).
time: Handles times (hour, minute, second, microsecond).
datetime: Combines date and time.
timedelta: Represents a duration (e.g., for date arithmetic).

It’s useful for tasks like logging timestamps, calculating durations, or formatting dates for display/output.

Importing the Module

Import the entire module or specific classes as needed:

import datetime  # Full module

# Or import specific classes
from datetime import datetime, date, time, timedelta

Getting Current Date and Time

Use datetime.now() to get the current local date and time as a datetime object.

import datetime

now = datetime.datetime.now()
print(now)  # Output: e.g., 2023-10-05 14:30:45.123456
print(type(now))  # <class 'datetime.datetime'>

For UTC time, use datetime.utcnow() (though preferably use datetime.now(timezone.utc) with imports from datetime.timezone for timezone awareness).

Creating Date and Time Objects

Construct objects manually with their constructors.

# Date: year, month, day
d = datetime.date(2023, 10, 5)
print(d)  # 2023-10-05

# Time: hour, minute, second, microsecond (optional)
t = datetime.time(14, 30, 45)
print(t)  # 14:30:45

# Datetime: combines date and time
dt = datetime.datetime(2023, 10, 5, 14, 30, 45)
print(dt)  # 2023-10-05 14:30:45

Omit parts that aren’t needed (e.g., datetime.datetime(2023, 10, 5) creates a datetime at midnight).

Formatting Dates (strftime)

Convert dates to strings using strftime with format codes (e.g., %Y for year, %m for month).

now = datetime.datetime.now()
formatted = now.strftime("%Y-%m-%d %H:%M:%S")
print(formatted)  # e.g., 2023-10-05 14:30:45

# Common formats:
# %A: Full weekday (e.g., Thursday)
# %B: Full month (e.g., October)
# %Y-%m-%d: ISO date

Parsing Dates from Strings (strptime)

Convert strings to datetime objects using strptime with matching formats.

date_str = "2023-10-05 14:30:45"
parsed = datetime.datetime.strptime(date_str, "%Y-%m-%d %H:%M:%S")
print(parsed)  # 2023-10-05 14:30:45
print(type(parsed))  # <class 'datetime.datetime'>

Match the format exactly, or it will raise a ValueError.

Date Arithmetic with timedelta

Add or subtract time intervals using timedelta.

now = datetime.datetime.now()
one_day = datetime.timedelta(days=1)
tomorrow = now + one_day
print(tomorrow)  # Current date + 1 day

# Subtract
yesterday = now - one_day

# Parts: days, seconds, microseconds, milliseconds, minutes, hours, weeks
one_week = datetime.timedelta(weeks=1)

For differences between dates:

date1 = datetime.datetime(2023, 10, 5)
date2 = datetime.datetime(2023, 10, 10)
delta = date2 - date1
print(delta.days)  # 5

Timezones (Advanced Usage)

For timezone-aware operations, use timezone (Python 3.3+). The module doesn’t handle timezone conversions natively; pair with pytz library for robust handling.

from datetime import datetime, timezone

# Naive datetime (no timezone)
naive = datetime.now()

# UTC aware
utc = datetime.now(timezone.utc)

# Custom timezone (requires tzinfo)
import pytz  # Might need pip install pytz
eastern = pytz.timezone("US/Eastern")
eastern_time = naive.astimezone(eastern)

Common Tips and Pitfalls

Immutable objects: datetime objects can’t be modified directly; arithmetics create new ones.
Month days: Use 29 for February in leap years; the module handles this with calendar or dateutil for leap checks.
Performance: Avoid frequent now() calls in loops; store the value.
Errors: Watch for invalid dates (e.g., date(2023, 2, 30) raises ValueError).
Library extensions: For advanced parsing, consider dateutil or arrow packages.

For full documentation, check Python’s official docs at docs.python.org. Practice with these examples in a Python interpreter.

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