date.toordinal() Date proleptic Gregorian ordinal of the date starting from Jan 1 year 1

toordinal : Return Proleptic Gregorian ordinal of the date starting with 1 as January 1 of year 1.
This represents the number of days since **January 1, 0001**. This method is useful for date calculations and comparisons.

How ordinal is used to get date by using fromordinal()

Today's ordinal vlaue

from datetime import date
my_ordinal=date.today().toordinal()
print("Today toordinal value : ", my_ordinal)

Output

Today toordinal value :  737319

Getting todays and tomorrows toordinal. We used timedelta here to get tomorrow's date object.

from datetime import date, datetime, timedelta 
print("Today toordinal : ", date.today().toordinal())
tomorrow=date.today() + timedelta(days=1)
print("Tomorrow toordinal : ", tomorrow.toordinal())

Output is here

Today toordinal :  737319
Tomorrow toordinal :  737320

We can create a date object and then get the value

import datetime
dt=datetime.datetime(2019,5,24) # Year, Month, date as input
print(dt.toordinal())

Output

We can check the above data ( todays date )

dt=datetime.datetime(2019,9,16) # Year, Month, date as input
print(dt.toordinal())

Output

Example 1: Finding the Difference Between Two Dates

We can use toordinal() to calculate the number of days between two dates.

from datetime import date

start_date = date(2024, 1, 1)  
end_date = date(2024, 12, 31)  

days_difference = end_date.toordinal() - start_date.toordinal()
print("Days between start and end date:", days_difference)

Example 2: Converting Ordinal to Date

We can use fromordinal() to convert an ordinal number back to a date.

from datetime import date

ordinal_value = 738000  
dt = date.fromordinal(ordinal_value)  
print("Date from ordinal:", dt)

Handling Edge Cases

Example 3: Handling Leap Year Differences

Leap years add complexity when calculating day differences. Let's check the effect of a leap year.

from datetime import date

date1 = date(2020, 2, 28)  
date2 = date(2020, 3, 1)  

print("Days between Feb 28 and Mar 1 in 2020:", date2.toordinal() - date1.toordinal())

Example 4: Checking the First Day of Each Year

We can find the ordinal value of the first day of any year.

from datetime import date

for year in range(2020, 2025):  
    print(f"First day of {year}:", date(year, 1, 1).toordinal())

Generating a Sequence of Dates

We can generate a sequence of dates by iterating over a range of ordinal values.

from datetime import date

start_date = date(2025, 2, 8)
end_date = date(2025, 2, 12)

for ordinal in range(start_date.toordinal(), end_date.toordinal() + 1):
    current_date = date.fromordinal(ordinal)
    print(current_date)

Use Cases for toordinal()

Sorting Dates Numerically: Convert dates to ordinal values for easier numerical sorting.
Date Range Calculations: Determine the number of days between two dates using ordinal values.
Historical Data Analysis: Track events or analyze trends based on sequential days.
Machine Learning Features: Use ordinal values as numerical features for date-based predictions.

All Date Objects fromordinal()

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Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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