pyspark: conditionals inside functions

[Franc Carter]

Hi,

I'm trying to write a short function that returns the last sunday of the
week of a given date, code below

def getSunday(day):

    day = day.cast("date")

    sun = next_day(day, "Sunday")

    n = datediff(sun,day)

    if (n == 7):

        return day

    else:

        return sun


this gives me

ValueError: Cannot convert column into bool:


Can someone point out what I am doing wrong

thanks


-- 
Franc