Python Intermediate Lesson 4: Dates, Formats and the Indian Financial Year

📎 This article includes 3 downloadable practice files ↓

📘 Python Intermediate Course · Lesson 4 of 10

Financial year helpers

def fy_label(d):
    y = d.year - (d.month < 4)
    return f"FY {y}-{str(y + 1)[2:]}"        # 2026-10-04 -> FY 2026-27

def fy_quarter(d):
    return f"Q{(d.month - 4) % 12 // 3 + 1}"  # Apr-Jun = Q1

Working days with holidays

def add_working_days(d, n, holidays=()):
    while n:
        d += dt.timedelta(days=1)
        if d.weekday() < 5 and d not in holidays:
            n -= 1
    return d

For whole calendars, numpy.busday_offset and pandas’ CustomBusinessDay do the same on millions of dates.

Common mistakes

• %m vs %M: %m is month, %M is minutes.
• Comparing a date with a datetime raises TypeError; convert with .date().

Practice

Unzip the practice data into a folder, put this lesson’s script in the same folder and run it (python pyi-NN.py). Compare with the expected output file. Then change one thing (a filter, a column, a format) and predict the new output before you run it.