Python program to find number of days between two given dates

Given two dates, Write a Python program to find the total number of days between them. 

Examples:

Input : dt1 = 13/12/2018, dt2 = 25/2/2019
Output : 74 days

Input : dt1 = 01/01/2004, dt2 = 01/01/2005
Output : 366 days 

Naive Approach: One Naive Solution is to start from dt1 and keep counting days till dt2 is reached. This solution requires more than O(1) time. 

A Better and Simple solution is to count the total number of days before dt1 from i.e., total days from 00/00/0000 to dt1, then count the total number of days before dt2. Finally, return the difference between the two counts.  

Python3

# Python3 program two find number of
# days between two given dates

# A date has day 'd', month 'm' and year 'y'


class Date:
    def __init__(self, d, m, y):
        self.d = d
        self.m = m
        self.y = y


# To store number of days in all months from
# January to Dec.
monthDays = [31, 28, 31, 30, 31, 30,
             31, 31, 30, 31, 30, 31]

# This function counts number of leap years
# before the given date


def countLeapYears(d):

    years = d.y

    # Check if the current year needs to be considered
    # for the count of leap years or not
    if (d.m <= 2):
        years -= 1

    # An year is a leap year if it is a multiple of 4,
    # multiple of 400 and not a multiple of 100.
    return int(years / 4) - int(years / 100) + int(years / 400)


# This function returns number of days between two
# given dates
def getDifference(dt1, dt2):

    # COUNT TOTAL NUMBER OF DAYS BEFORE FIRST DATE 'dt1'

    # initialize count using years and day
    n1 = dt1.y * 365 + dt1.d

    # Add days for months in given date
    for i in range(0, dt1.m - 1):
        n1 += monthDays[i]

    # Since every leap year is of 366 days,
    # Add a day for every leap year
    n1 += countLeapYears(dt1)

    # SIMILARLY, COUNT TOTAL NUMBER OF DAYS BEFORE 'dt2'

    n2 = dt2.y * 365 + dt2.d
    for i in range(0, dt2.m - 1):
        n2 += monthDays[i]
    n2 += countLeapYears(dt2)

    # return difference between two counts
    return (n2 - n1)


# Driver program
dt1 = Date(13, 12, 2018)
dt2 = Date(25, 2, 2019)

print(getDifference(dt1, dt2), "days")

Output:

74 days

Time Complexity: O(1)
Auxiliary Space: O(1)

Using Python datetime module:

Python comes with an inbuilt datetime module that helps us to solve various datetime related problems. In order to find the difference between two dates we simply input the two dates with date type and subtract them, which in turn provides us the number of days between the two dates. 

Python3

# Python3 program to find number of days
# between two given dates
from datetime import date

def numOfDays(date1, date2):
    return (date2-date1).days

# Driver program
date1 = date(2018, 12, 13)
date2 = date(2019, 2, 25)
print(numOfDays(date1, date2), "days")

Time Complexity: O(1)
Auxiliary Space: O(1)