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Calculate Last Friday of Month in Pandas

I've written this function to get the last Thursday of the month

def last_thurs_date(date):
    cal = calendar.monthcalendar(year, month)
    last_thurs_date = cal[4][4]
    if month < 10:
        thurday_date = str(year)+'-0'+ str(month)+'-' + str(last_thurs_date)
        thurday_date = str(year) + '-' + str(month) + '-' + str(last_thurs_date)
    return thurday_date

But its not working with the lambda function.

datelist['Date'].map(lambda x: last_thurs_date(x))

Where datelist is

datelist = pd.DataFrame(pd.date_range(start = pd.to_datetime('01-01-2014',format='%d-%m-%Y')
                                      , end = pd.to_datetime('06-03-2019',format='%d-%m-%Y'),freq='D').tolist()).rename(columns={0:'Date'})


  • Jpp already added the solution, but just to add a slightly more readable formatted string - see this awesome website.

    import calendar
    def last_thurs_date(date):
        year, month = date.year, date.month
        cal = calendar.monthcalendar(year, month)
        # the last (4th week -> row) thursday (4th day -> column) of the calendar
        # except when 0, then take the 3rd week (February exception)
        last_thurs_date =  cal[4][4] if cal[4][4] > 0 else cal[3][4] 
        return f'{year}-{month:02d}-{last_thurs_date}'

    Also added a bit of logic - e.g. you got 2019-02-0 as February doesn't have 4 full weeks.