Date Calculator Script

Beginner Python
datetimetimedeltadateutilstrftimetimezone

Objective

Build a date calculation utility: compute differences, add/subtract time periods, and handle timezones.

Tools & Technologies

  • datetime
  • timedelta
  • dateutil
  • strftime
  • timezone

Key Commands

from datetime import datetime, timedelta
datetime.strptime('2024-01-15','%Y-%m-%d')
(d2-d1).days
datetime.now(timezone.utc)

Architecture Overview

flowchart LR INPUT[Date string\n'2024-01-15'] --> PARSE[strptime\nparse to datetime] PARSE --> ARITH[Arithmetic\n+ timedelta\n- timedelta] ARITH --> COMPARE[Compare\nd1 < d2] ARITH --> FORMAT[strftime\nformat to string] FORMAT --> OUTPUT[Output\n'January 15, 2024'] style PARSE fill:#1a1a2e,stroke:#00d4ff,color:#e0e0e0 style OUTPUT fill:#1a1a2e,stroke:#00ff88,color:#e0e0e0

Step-by-Step Process

01
Date Arithmetic

Add and subtract time periods.

from datetime import datetime, timedelta

now = datetime.now()
print(f'Today: {now.strftime("%Y-%m-%d")}')

# Add 30 days
future = now + timedelta(days=30)
print(f'In 30 days: {future.strftime("%Y-%m-%d")}')

# Difference between dates
birthday = datetime(1999, 7, 15)
age_days = (now - birthday).days
print(f'Age in days: {age_days}')
print(f'Age in years: {age_days // 365}')
02
Parse and Format

Convert between strings and datetime objects.

# Parse various formats
d1 = datetime.strptime('2024-01-15', '%Y-%m-%d')
d2 = datetime.strptime('15/01/2024', '%d/%m/%Y')
d3 = datetime.strptime('January 15, 2024', '%B %d, %Y')

# Format
print(d1.strftime('%B %d, %Y'))     # January 15, 2024
print(d1.strftime('%Y-%m-%dT%H:%M')) # 2024-01-15T00:00
print(d1.isoformat())                # ISO 8601

Challenges & Solutions

  • Naive datetime (no timezone) comparisons with aware datetime (with tz) raise TypeError
  • strptime format must match exactly — extra spaces cause ValueError

Key Takeaways

  • Store all datetimes as UTC internally, convert to local time only for display
  • zoneinfo (Python 3.9+) is the standard library alternative to pytz