How I set default value to zope.schema.datetime?

I codding a product using Python Dexterity Type, and I have one field shema.Datetime (see below), And I want set a default date time when form was create in Plone.

I tried using Zope DateTime and Python DateTime, and don't work. In docs zope schema don't have examples for this.

# I'm tried use this options with DateTime
from DateTime import DateTime
# DateTimeNow = DateTime()
# DateTimeNow = DateTime().asdatetime()

# And tried use datetime
import datetime
DateTimeNow = datetime.datetime.now()

class IDigitalFile(model.Schema):
    ...

    uploded_at = schema.Datetime(
        title=_(u"Data de Upload"),
        required=True,
        defaultFactory=DateTimeNow,
    )

So, How I set default value in this case?

The solution is using Python Datetime, and not Zope DateTime, see code:

from datetime import datetime
...
def nowDateTime():
    return datetime.today()

...
directives.mode(uploded_at="hidden")
uploded_at = schema.Datetime(
    title=_(u"Data de Upload"),
    required=True,
    defaultFactory=nowDateTime,
)