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Unit 9 • Lesson 6

Working with Dates and Times

Overview

Many applications require tracking dates, times, or durations. This topic covers using the datetime module to perform calculations, format timestamps, and build programs that rely on scheduling or time tracking, handling temporal data effectively.

Beginner 20–25 min
Next: Data Visualization with Matplotlib All Units

What You Will Learn in This Lesson

By the end of this lesson, you will know:

  • datetime module: Working with dates, times, and timestamps.
  • Creating dates: How to create date and datetime objects.
  • Formatting dates: Converting dates to strings and parsing strings to dates.
  • Time differences: Calculating durations with timedelta.
  • Date arithmetic: Adding and subtracting time from dates.

The datetime Module

Python's datetime module provides classes for working with dates and times:

datetime

Date and time together (year, month, day, hour, minute, second)

date

Just the date (year, month, day)

time

Just the time (hour, minute, second)

timedelta

Time differences and durations

Working with datetime
from datetime import datetime, date, timedelta

# Get current date and time
now = datetime.now()
print(now)  # Output: 2024-01-15 14:30:45.123456

# Create a specific date
birthday = date(2000, 5, 15)
print(birthday)  # Output: 2000-05-15

# Calculate time difference
future = datetime.now() + timedelta(days=30)
print(future)  # Output: 30 days from now

Formatting Dates

Convert dates to strings and parse strings to dates using format codes:

Date Formatting with strftime()
from datetime import datetime

# Get current date and time
now = datetime.now()

# Format date as string
formatted1 = now.strftime("%B %d, %Y")
print(formatted1)  # Output: January 15, 2024

formatted2 = now.strftime("%Y-%m-%d %H:%M:%S")
print(formatted2)  # Output: 2024-01-15 14:30:45

formatted3 = now.strftime("%A, %B %d, %Y")
print(formatted3)  # Output: Monday, January 15, 2024
Parsing Strings to Dates with strptime()
from datetime import datetime

# Parse string to date
date_string1 = "2024-01-15"
parsed_date1 = datetime.strptime(date_string1, "%Y-%m-%d")
print(parsed_date1)  # Output: 2024-01-15 00:00:00

date_string2 = "January 15, 2024"
parsed_date2 = datetime.strptime(date_string2, "%B %d, %Y")
print(parsed_date2)  # Output: 2024-01-15 00:00:00

Common Format Codes

Code Meaning Example
%Y 4-digit year 2024
%m Month as number (01-12) 01
%d Day of month (01-31) 15
%B Full month name January
%A Full weekday name Monday
%H Hour (00-23) 14
%M Minute (00-59) 30
%S Second (00-59) 45

Time Differences and Calculations

Use timedelta to work with time differences:

Working with timedelta
from datetime import datetime, timedelta

# Get current time
now = datetime.now()
print(f"Now: {now}")

# Add time
future = now + timedelta(days=30)
print(f"30 days from now: {future}")

# Subtract time
past = now - timedelta(hours=5)
print(f"5 hours ago: {past}")

# Calculate difference
date1 = datetime(2024, 1, 1)
date2 = datetime(2024, 1, 15)
difference = date2 - date1
print(f"Difference: {difference.days} days")

timedelta Parameters

You can specify days, seconds, microseconds, milliseconds, minutes, hours, or weeks:

  • timedelta(days=7) - 7 days
  • timedelta(hours=24) - 24 hours
  • timedelta(weeks=2) - 2 weeks
  • timedelta(days=1, hours=12) - 1.5 days

Practice: Working with Dates

Try It Yourself

Try working with dates and times:

Press Run to see output

What happened? You created a date, formatted it as a string, calculated the difference between dates, and added time using timedelta.

Working with Timezones

For applications that need timezone awareness:

Timezone-Aware datetime
from datetime import datetime
import pytz  # Need to install: pip install pytz

# Create timezone-aware datetime
utc = pytz.UTC
now_utc = datetime.now(utc)
print(f"UTC time: {now_utc}")

# Convert to different timezone
ny_tz = pytz.timezone('America/New_York')
ny_time = now_utc.astimezone(ny_tz)
print(f"New York time: {ny_time}")

Note

For most beginner projects, you don't need timezones. But if you're building applications that work across regions, timezone handling becomes important!

Common Date/Time Operations

Here are common operations you'll perform:

Calculating Age
from datetime import datetime

def calculate_age(birth_date):
    today = datetime.now()
    age = today.year - birth_date.year
    # Adjust if birthday hasn't occurred this year
    if (today.month, today.day) < (birth_date.month, birth_date.day):
        age -= 1
    return age

birthday = datetime(2000, 5, 15)
age = calculate_age(birthday)
print(f"Age: {age} years")
Finding Days Between Dates
from datetime import datetime, timedelta

def days_between(date1, date2):
    return abs((date2 - date1).days)

start = datetime(2024, 1, 1)
end = datetime(2024, 12, 31)
days = days_between(start, end)
print(f"Days between: {days}")
Working with Weekdays
from datetime import datetime, timedelta

def get_next_weekday(date, weekday):
    """Get next occurrence of weekday (0=Monday, 6=Sunday)"""
    days_ahead = weekday - date.weekday()
    if days_ahead <= 0:
        days_ahead += 7
    return date + timedelta(days=days_ahead)

today = datetime.now()
next_monday = get_next_weekday(today, 0)
print(f"Next Monday: {next_monday.strftime('%B %d, %Y')}")

Summary

In this lesson, you learned:

  • datetime module: Classes for dates, times, and durations
  • Creating dates: Use datetime.now() or datetime(year, month, day)
  • Formatting: Use strftime() to format, strptime() to parse
  • Time differences: Use timedelta for calculations
  • Date arithmetic: Add/subtract timedelta from dates
  • Common operations: Age calculation, days between dates, weekday operations

Remember

Dates and times are essential for many applications - logging, scheduling, data analysis, timestamps. The datetime module makes it easy to work with temporal data. Practice with common operations like calculating ages and finding date differences!

End-of-Lesson Exercises

Think about these questions to reinforce what you've learned:

Exercise 1: datetime Classes

What are the main classes in the datetime module? What does each one represent?

Exercise 2: Date Operations

How would you calculate a date 30 days from now? How would you format it as "January 15, 2024"?

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