Hi everyone;i'm trying to add constraints of unicity;i can show the message in the beginning but after 2 tests i show this message: UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 27: ordinal not in range(128) any idea please

myclass.py

class time_table_line(osv.osv): _description ='Time Table Line' _name = 'time.table.line' _rec_name ="table_id" _columns = {

    'teacher_id': fields.many2one('hr.employee', 'Nom du professeur',),
    'subject_id': fields.many2one('subject.subject', 'Nom de la matiere'),
    'table_id': fields.many2one('time.table', 'TimeTable'),
    'start_time' : fields.datetime('Start Time', required=True ),
    'end_time' : fields.float('End Time', required=True ),
    'sale_id' : fields.many2one('school.sale', 'Salle',required=True ),
}
_sql_constraints = [
('sale', 'unique(sale_id,start_time,end_time)', 'Salle existante')
]

_sql_constraints = [
('prof', 'unique(teacher_id,start_time,end_time)', 'Prof existant')
]

time_table_line()