How to Compute the Third‑Last Workday of a Month Using Python

Introduction

In a recent Python discussion, a user asked how to quickly calculate the third last workday of the current month. Existing searches on CSDN and ChatGPT did not yield a satisfactory answer, so a custom solution was developed.

Implementation

Using ChatGPT’s suggestion, the following Python code determines the month’s last day, backs up to the previous workday, and then steps back two more workdays to obtain the third last workday.

import datetime

def get_third_last_workday(year, month):
    # Find the last day of the month
    last_day = datetime.date(year, month, 1) + datetime.timedelta(days=31)
    last_day -= datetime.timedelta(days=last_day.day)
    # Move back until a weekday is found
    while True:
        if last_day.weekday() < 5:
            break
        last_day -= datetime.timedelta(days=1)
    # Step back two more workdays to get the third last workday
    third_last_workday = last_day - datetime.timedelta(days=2)
    while True:
        if third_last_workday.weekday() < 5:
            break
        third_last_workday -= datetime.timedelta(days=1)
    return third_last_workday

# Example
print(get_third_last_workday(2023, 6))  # Output: 2023-06-28

The script correctly returns the desired date, demonstrating a practical approach to date arithmetic in Python.

Conclusion

The article presents a clear Python‑based method for solving the “third last workday” problem, offering both the reasoning and a ready‑to‑run code snippet that readers can adapt to their own projects.