Comparing dates in Python

Comparing dates is quite easy in Python. Dates can be easily compared using comparison operators (like <, >, <=, >=, != etc.). Let’s see how to compare dates with the help of datetime module using Python. 

Code #1 : Basic 

Python3

# Simple Python program to compare dates

# importing datetime module
import datetime

# date in yyyy/mm/dd format
d1 = datetime.datetime(2018, 5, 3)
d2 = datetime.datetime(2018, 6, 1)

# Comparing the dates will return
# either True or False
print("d1 is greater than d2 : ", d1 > d2)
print("d1 is less than d2 : ", d1 < d2)
print("d1 is not equal to d2 : ", d1 != d2)

Output :

d1 is greater than d2 :  False
d1 is less than d2 :  True
d1 is not equal to d2 :  True

Code #2 : Sorting dates One of the best ways to sort a group of dates is to store them into a list and apply sort() method. This will sort all the dates which are available in the list. One can store the date class objects into the list using append() method. 

Python3

# Python program to sort the dates

# importing datetime module
from datetime import *

# create empty list
group = []

# add today's date
group.append(date.today())

# create some more dates
d = date(2015, 6, 29)
group.append(d)

d = date(2011, 4, 7)
group.append(d)

# add 25 days to the date
# and add to the list
group.append(d + timedelta(days = 25))

# sort the list
group.sort()

# print the dates
for d in group:
    print(d)

Output :

2011-04-07
2011-05-02
2015-06-29
2018-05-24

Code #3 : Comparing Dates Compare two date class objects, just like comparing two numbers. 

Python3

# importing datetime module
from datetime import *

# Enter birth dates and store
# into date class objects
d1, m1, y1 = [int(x) for x in input("Enter first"
        " person's date(DD/MM/YYYY) : ").split('/')]

b1 = date(y1, m1, d1)

# Input for second date
d2, m2, y2 = [int(x) for x in input("Enter second"
        " person's date(DD/MM/YYYY) : ").split('/')]

b2 = date(y2, m2, d2)

# Check the dates
if b1 == b2:
    print("Both persons are of equal age")

elif b1 > b2:
    print("The second person is older")

else:
    print("The first person is older")

Output :

Enter first person's date(DD/MM/YYYY) : 12/05/2017
Enter second person's date(DD/MM/YYYY) : 10/11/2015
The second person is older

CODE 4: Using timedelta.

APPROACH:

This code compares two date objects in Python using the date and timedelta modules. It uses the subtraction operator to calculate the difference between the dates, and then compares the result to a timedelta object with a value of 0 to determine whether one date is greater than, less than, or equal to the other. The if statements are used to print the results of the comparisons.

ALGORITHM:

1.Import the datetime and timedelta modules.
2.Create two date objects d1 and d2 with year, month and day values.
3.Calculate the difference between the dates using the subtraction (-) operator and compare it to timedelta(0) to determine whether d1 is greater than

Python3

from datetime import date, timedelta

d1 = date(2022, 4, 1)
d2 = date(2023, 4, 1)

# Comparing dates
if d1 - d2 > timedelta(0):
    print("d1 is greater than d2 : ", True)
else:
    print("d1 is greater than d2 : ", False)

if d1 - d2 < timedelta(0):
    print("d1 is less than d2 : ", True)
else:
    print("d1 is less than d2 : ", False)

if d1 != d2:
    print("d1 is not equal to d2 : ", True)
else:
    print("d1 is not equal to d2 : ", False)

Output

d1 is greater than d2 :  False
d1 is less than d2 :  True
d1 is not equal to d2 :  True

Time complexity: O(1)

The time complexity of the subtraction (-) operator between two date objects is O(1).

Auxiliary Space: O(1)

The space complexity of this code is O(1) because only two date objects and one timedelta object are used, and the memory usage does not increase with the input size.