How to Determine Last Friday's Date using Python?

In this article, we will learn how to determine last Friday's date using Python. This is useful for scheduling, reporting, and date-based calculations in business applications.

Methods Used

The following are the various methods to accomplish this task

• Using datetime module

• Using dateutil package

Method 1: Using Datetime Module

This approach uses Python's built-in datetime module to calculate the previous Friday by determining the current weekday and counting backwards.

Algorithm

Following are the steps to perform this task

• Import datetime and timedelta from datetime module

• Create a list of weekday names for reference

• Define a function to find the previous occurrence of any given day

• Calculate the difference between current day and target day

• Subtract the appropriate number of days to get the previous date

Example

The following program returns the last Friday's date using datetime module

# importing datetime, timedelta from datetime module
from datetime import datetime, timedelta

# list of days in a week
weekdays_list = ['Monday', 'Tuesday', 'Wednesday', 'Thursday',
                 'Friday', 'Saturday', 'Sunday']

# creating a function to return the last weekday of input day
def get_previous_weekday(input_day, start_date=None):
    # check whether the start date is None
    if start_date is None:
        # assigning today's date(current date) to the start date
        start_date = datetime.today()
    
    # getting the current weekday number (0=Monday, 6=Sunday)
    current_day_number = start_date.weekday()
    
    # get the index of the target weekday
    target_day_number = weekdays_list.index(input_day)
    
    # calculate how many days ago the target day occurred
    days_ago = (7 + current_day_number - target_day_number) % 7
    
    # if target day is today, go back to previous week
    if days_ago == 0:
        days_ago = 7
    
    # subtract the number of days to get the target date
    target_date = start_date - timedelta(days=days_ago)
    
    return target_date

# printing today's current date and time
print("Current date and time:", datetime.today())

# printing the last Friday date
print("Last Friday Date:", get_previous_weekday('Friday'))

# printing other previous weekdays
print("Last Monday Date:", get_previous_weekday('Monday'))
print("Last Wednesday Date:", get_previous_weekday('Wednesday'))

The output of the above code is

Current date and time: 2023-01-01 08:15:35.935826
Last Friday Date: 2022-12-30 08:15:35.936020
Last Monday Date: 2022-12-26 08:15:35.936153
Last Wednesday Date: 2022-12-28 08:15:35.936264

Method 2: Using Dateutil Package

The dateutil package provides more sophisticated date manipulation capabilities. It uses relativedelta which supports operations with years, months, weeks, and specific weekdays.

The dateutil.relativedelta.relativedelta adds support for periods defined in terms of years, months, weeks, or days, whereas timedelta only supports days and weeks.

Example

The following program returns last Friday's and next Friday's date using dateutil module

# importing datetime from datetime module
from datetime import datetime

# importing relativedelta from dateutil module
from dateutil.relativedelta import relativedelta
from dateutil.rrule import FR

# taking the start date as the current date
start_date = datetime.now()

# printing today's current date and time
print("Current Date:", start_date)

# printing the next Friday date
print("Next Friday Date:", start_date + relativedelta(weekday=FR))

# printing the last Friday date
print("Last Friday Date:", start_date + relativedelta(weekday=FR(-1)))

The output of the above code is

Current Date: 2023-01-15 08:19:49.267666
Next Friday Date: 2023-01-20 08:19:49.267666
Last Friday Date: 2023-01-13 08:19:49.267666

Comparison

Conclusion

Both methods effectively determine last Friday's date. Use the datetime module for simple cases without external dependencies, or dateutil for more complex date calculations with cleaner syntax.