<input type="text" name="credit_card[billing_address][region]" />

http://www.braintreepaymentsolutions.com/docs/python/credit_cards/cre...

The only way I see to support these field names is to use BaseForm and
give up several of the features that make WTForms so useful.  Is there
a way to define a Form using the normal class-attribute-fields
approach, while assigning each Field a special string to use as its
name when rendering html?

If not, perhaps it would be worth adding, for the sake of easily
handling all the characters allowed by html forms.  I imagine the
interface might something like this:

class MyForm(Form):
  region = TextField( "Region", name="credit_card[billing_address]
[region]")