How to compare date strings in Python?

Python's datetime module makes comparing dates straightforward by supporting all comparison operators (<, >, <=, >=, ==, !=). This is essential for date validations, sorting, and conditional logic in your applications.

Basic Date Comparison

Here's how to compare datetime objects using comparison operators ?

from datetime import datetime, timedelta

today = datetime.today()
yesterday = today - timedelta(days=1)

print("Today:", today.strftime("%Y-%m-%d"))
print("Yesterday:", yesterday.strftime("%Y-%m-%d"))
print()
print("today < yesterday:", today < yesterday)
print("today > yesterday:", today > yesterday)
print("today == yesterday:", today == yesterday)

Today: 2024-01-15
Yesterday: 2024-01-14

today < yesterday: False
today > yesterday: True
today == yesterday: False

Comparing Date Strings

When working with date strings, convert them to datetime objects first for accurate comparison ?

from datetime import datetime

# Date strings in different formats
date1_str = "2024-01-15"
date2_str = "2024-01-20"
date3_str = "15/01/2024"

# Convert to datetime objects
date1 = datetime.strptime(date1_str, "%Y-%m-%d")
date2 = datetime.strptime(date2_str, "%Y-%m-%d")
date3 = datetime.strptime(date3_str, "%d/%m/%Y")

print("date1 < date2:", date1 < date2)
print("date1 == date3:", date1 == date3)
print("date2 > date3:", date2 > date3)

date1 < date2: True
date1 == date3: True
date2 > date3: True

Practical Example: Age Verification

Here's a practical example checking if someone is old enough ?

from datetime import datetime

def is_old_enough(birth_date_str, min_age=18):
    birth_date = datetime.strptime(birth_date_str, "%Y-%m-%d")
    today = datetime.today()
    age_in_days = (today - birth_date).days
    age_in_years = age_in_days / 365.25
    
    return age_in_years >= min_age

# Test with different birth dates
birth_dates = ["2000-05-15", "2010-03-20", "1995-12-01"]

for birth_date in birth_dates:
    result = is_old_enough(birth_date)
    print(f"Born {birth_date}: Old enough? {result}")

Born 2000-05-15: Old enough? True
Born 2010-03-20: Old enough? False
Born 1995-12-01: Old enough? True

Comparison Summary

Conclusion

Always convert date strings to datetime objects using strptime() before comparing. Python's datetime comparison operators make date validation and sorting intuitive and reliable.