'Formats the date as "%Y-%m-%d %H:%M:%S" with the sep param between the
date and time portions
:param set:
A single character of the separator to place between the date and
time
:return:
The formatted datetime as a unicode string in Python 3 and a byte
string in Python 2'

def isoformat(self, sep=u'T'):

    if (self.microsecond == 0):
        return self.strftime((u'0000-%%m-%%d%s%%H:%%M:%%S' % sep))
    return self.strftime((u'0000-%%m-%%d%s%%H:%%M:%%S.%%f' % sep))
