# -*- coding: utf-8 -*-
from openerp import fields, models

class Session(models.Model):
    _name = 'openacademy.session'

    name = fields.Char(required=True)
    start_date = fields.Date()
    duration = fields.Float(digits=(6, 2), help="Duration in days")
    seats = fields.Integer(string="Number of seats")
    instructor_id = fields.Many2one('res.partner', string="Instructor")
    course_id = fields.Many2one('openacademy.course',
        ondelete='cascade', string="Course", required=True)
    attendee_ids = fields.Many2many('res.partner', string="Attendees")

# -*- coding: utf-8 -*-
from openerp import fields, models


class Session(models.Model):
    _name = 'openacademy.session'

    name = fields.Char(required=True)
    start_date = fields.Date()
    duration = fields.Float(digits=(6, 2), help="Duration in days")
    seats = fields.Integer(string="Number of seats")
    instructor_id = fields.Many2one('res.partner', string="Instructor",
        domain=['|', ('instructor', '=', True),
                     ('category_id.name', 'ilike', "Teacher")])
    course_id = fields.Many2one('openacademy.course',
                                ondelete='cascade', string="Course",
                                required=True)
    attendee_ids = fields.Many2many('res.partner', string="Attendees")

Add domain or and ilike