In docassemble version 0.2.23 there has been a significant change to the way that date fields work.  Before, setting "datatype: date" resulted in a variable that was simply a text string like "2018-01-01."  Now, the variable will be a Python object representing the date.

This means that you do not have to use the as_datetime() function on variables defined by datatype: date fields.

This change is unlikely to "break" existing interviews, since docassemble's date functions will work the same regardless of whether their input is a text date or a Python object.  However, you will see a difference in the default formatting of a date.  Before, writing ${ user.birthdate }, or {{ user.birthdate }} in a .docx file, would yield something like "1985-01-03," but now it will yield "January 3, 1985." 

For more information, see the documentation:
* https://docassemble.org/docs/fields.html#date
* https://docassemble.org/docs/objects.html#DADateTime