lambda callable in foreignkey default

I ran into a strange issue today when trying to use a lambda function for the default value of a ForeignKey.

my original code was this, and I expected it would look for RestaurantType instances whenever I would try to create a Restaurant:
type_of_restaurant = models.ForeignKey(RestaurantType, default = lambda: RestaurantType.objects.all()[0])

but to my surprise it would run the query when the models where loaded!

I changed to this and it behaved as I expected:
type_of_restaurant = models.ForeignKey(RestaurantType, default = lambda: RestaurantType.objects.get(id = 1))

Anyone could explain me why ? Is there something counter-intuitive with the evaluation order of the brackets or something ?

Regards,
Philippe

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