How to clear the field when the constrain or warning message is raised 

@api.onchange('mobile', 'mobile2', 'laneline', 'pan_card', 'aadhar_no', 'bank_account_no')
def onchange_check_supplier(self):
    duplicate_mobile = ' '
    duplicate_alternate_mobile = ' '
    duplicate_laneline = ' '
    duplicate_pan_card = ' '
    duplicate_aadhar_no = ' '
    duplicate_bank_account_no = ' '
    if self.mobile:
        duplicate_mobile = self.mobile.isdigit()
        if duplicate_mobile == False:
            raise UserError(_('You must enter a correct mobile no'))
    if self.mobile2:
        duplicate_alternate_mobile = self.mobile2.isdigit()
        if duplicate_alternate_mobile == False:
            raise UserError(_('You must enter a correct alternate mobile no'))
    if self.bank_account_no:
        duplicate_bank_account_no = self.bank_account_no.isdigit()
        if duplicate_bank_account_no == False:
            raise UserError(_('You must enter a correct Bank Account no'))
    if self.aadhar_no:
        duplicate_aadhar_no = self.aadhar_no.isdigit()
        if duplicate_aadhar_no == False:
            raise UserError(_('You must enter a correct Aadhar card no'))
    if self.laneline:
        duplicate_laneline = self.laneline.isdigit()
        if duplicate_laneline == False:
            raise UserError(_('You must enter a correct LandLine no'))
    if self.pan_card:
        duplicate_pan_card = self.pan_card.isalnum()
        if duplicate_pan_card == False:
            raise UserError(_('You must enter a correct Pan card no'))

i tried this method but it not working for me