Fix default value handling for dotted sources by rpkilby · Pull Request #5375 · encode/django-rest-framework (original) (raw)

I had originally just moved the guard, as I thought it was possible for the instance to be None. However, that is never the case due to the following:

• Serialization implies that the incoming instance cannot be None (here).
• The get_attribute() function is only invoked through serialization (here).

Given the above, the instance can only be set to None when iterating over the attrs list. With the guard, None is then returned. Without the guard, a subsequent attr would cause an AttributeError to be raised instead, allowing the default to be used.

with guard

get_attribute({'a': {'b': None}}, ['a', 'b', 'c']) None

without guard

get_attribute({'a': {'b': None}}, ['a', 'b', 'c']) Traceback (most recent call last): File "", line 1, in File "/Users/bagel/Documents/django-rest-framework/rest_framework/fields.py", line 100, in get_attribute instance = getattr(instance, attr) AttributeError: 'NoneType' object has no attribute 'c'