pySpark/Python iterate through dataframe columns, check for a condition and populate another colum

I am working with python/pySpark in Jupyter Notebook and I am trying to figure out the following:

I've got a dataframe like

MainDate      Date1        Date2        Date3         Date4
2015-10-25    2015-09-25   2015-10-25   2015-11-25    2015-12-25
2012-07-16    2012-04-16   2012-05-16   2012-06-16    2012-07-16
2005-03-14    2005-07-14   2005-08-14   2005-09-14    2005-10-14

I need to compare MainDate with each of the Date1-Date4 and if MainDate == Date# then to create a new column REAL = Date#, if there is no match then REAL = "None", all the dates are in Date format, also the real dataframe has Date1 to Date72 and there could be only one match, if there is any

Final result:

MainDate      Date1        Date2        Date3         Date4        REAL
2015-10-25    2015-09-25   2015-10-25   2015-11-25    2015-12-25   Date2
2012-07-16    2012-04-16   2012-05-16   2012-06-16    2012-07-16   Date4
2005-03-14    2005-07-14   2005-08-14   2005-09-14    2005-10-14   None

Thanks in advance