[Django] ChoiceFieldに初期値を与える

環境
Python 3.5.0
Django 1.9.2

forms.py

CAKE_CHOICES = (
    (1, 'いちごケーキ'),
    (2, 'チョコケーキ'),
    (3, 'チーズケーキ')
)

class CakeForm(forms.Form):
    medal = ChoiceField(widget=Select, choices=MEDAL_CHOICES)

    class Meta:
        model = Cake

views.py

cake_form = CakeForm(initial = {
    'selected_cake': 2  # チョコケーキを初期値に設定
})