Can't add a field with an election

I'm student. Please don't scold me.

models.py:

from django.db import models


class Teacher(models.Model):
    MATH = 'MT'
    PHYS = 'PH'
    COMP = 'CS'
    SUBJECTS_TEACHER_CHOICES = {
        MATH: 'Math',
        PHYS: 'Phys',
        COMP: 'Comp',
    }
    subjects = models.CharField(
        max_length=2,
        choices=SUBJECTS_TEACHER_CHOICES,
        default=MATH,
    )
    first_name = models.CharField(max_length=128)

error: ERRORS: TeachersApp.Teacher.subjects: (fields.E005) 'choices' must be an iterable containing (actual value, human readable name) tuples.

I want to add a field with choices.

Answer

Oh, okay. My version of django doesn't support that format.