Function returns datetime in openerp

I am trying to create a function that returns date and time, but it doesn't work. It returns error code 2:

def _date_(self, cr, uid, ids, fields, arg, context):
    x={}
    for record in self.browse(cr, uid, ids):
        if record.date :
            a = datetime.strptime(record.date, "%Y-%m-%d %H:%M:%S")
            b = a.strftime("%Y-%m-%d %H:%M:%S")
            x[record.id] = b
        return x

_columns = {
    'date': fields.datetime('Date-Hour of Call', required=True),    
    'date_': fields.function(_date_, string='date copy'),

      

        
        
        
      

    

Regards,