I ran into cpython issue #24931.
The _asdict() function of my namedtuple subclasses returned empty
dictionaries. My subclass implicitly created an instance dictionary
(c.f. empty __slots__). This broke the Python 3.4 version of _asdict.
When you see the source of the namedtuple that is implemented it becomes clear why this happens.
| # Python 3.4 | |
| In [2]: collections.namedtuple('A', ['a', 'b', 'c'], verbose=True) [1/23] | |
| from builtins import property as _property, tuple as _tuple | |
| from operator import itemgetter as _itemgetter | |
| from collections import OrderedDict | |
| class A(tuple): | |
| 'A(a, b, c)' | |
| __slots__ = () | |
| _fields = ('a', 'b', 'c') | |
| def __new__(_cls, a, b, c): | |
| 'Create new instance of A(a, b, c)' | |
| return _tuple.__new__(_cls, (a, b, c)) | |
| @classmethod | |
| def _make(cls, iterable, new=tuple.__new__, len=len): | |
| 'Make a new A object from a sequence or iterable' | |
| result = new(cls, iterable) | |
| if len(result) != 3: | |
| raise TypeError('Expected 3 arguments, got %d' % len(result)) | |
| return result | |
| def _replace(_self, **kwds): | |
| 'Return a new A object replacing specified fields with new values' | |
| result = _self._make(map(kwds.pop, ('a', 'b', 'c'), _self)) | |
| if kwds: | |
| raise ValueError('Got unexpected field names: %r' % list(kwds)) | |
| return result | |
| def __repr__(self): | |
| 'Return a nicely formatted representation string' | |
| return self.__class__.__name__ + '(a=%r, b=%r, c=%r)' % self | |
| @property | |
| def __dict__(self): | |
| 'A new OrderedDict mapping field names to their values' | |
| return OrderedDict(zip(self._fields, self)) | |
| def _asdict(self): | |
| 'Return a new OrderedDict which maps field names to their values.' | |
| return self.__dict__ | |
| def __getnewargs__(self): | |
| 'Return self as a plain tuple. Used by copy and pickle.' | |
| return tuple(self) | |
| def __getstate__(self): | |
| 'Exclude the OrderedDict from pickling' | |
| return None | |
| a = _property(_itemgetter(0), doc='Alias for field number 0') | |
| b = _property(_itemgetter(1), doc='Alias for field number 1') | |
| c = _property(_itemgetter(2), doc='Alias for field number 2') | |
| Out[2]: __main__.A |
| # Python 3.5 | |
| In [2]: collections.namedtuple('A', ['a', 'b', 'c'], verbose=True) | |
| from builtins import property as _property, tuple as _tuple | |
| from operator import itemgetter as _itemgetter | |
| from collections import OrderedDict | |
| class A(tuple): | |
| 'A(a, b, c)' | |
| __slots__ = () | |
| _fields = ('a', 'b', 'c') | |
| def __new__(_cls, a, b, c): | |
| 'Create new instance of A(a, b, c)' | |
| return _tuple.__new__(_cls, (a, b, c)) | |
| @classmethod | |
| def _make(cls, iterable, new=tuple.__new__, len=len): | |
| 'Make a new A object from a sequence or iterable' | |
| result = new(cls, iterable) | |
| if len(result) != 3: | |
| raise TypeError('Expected 3 arguments, got %d' % len(result)) | |
| return result | |
| def _replace(_self, **kwds): | |
| 'Return a new A object replacing specified fields with new values' | |
| result = _self._make(map(kwds.pop, ('a', 'b', 'c'), _self)) | |
| if kwds: | |
| raise ValueError('Got unexpected field names: %r' % list(kwds)) | |
| return result | |
| def __repr__(self): | |
| 'Return a nicely formatted representation string' | |
| return self.__class__.__name__ + '(a=%r, b=%r, c=%r)' % self | |
| def _asdict(self): | |
| 'Return a new OrderedDict which maps field names to their values.' | |
| return OrderedDict(zip(self._fields, self)) | |
| def __getnewargs__(self): | |
| 'Return self as a plain tuple. Used by copy and pickle.' | |
| return tuple(self) | |
| a = _property(_itemgetter(0), doc='Alias for field number 0') | |
| b = _property(_itemgetter(1), doc='Alias for field number 1') | |
| c = _property(_itemgetter(2), doc='Alias for field number 2') | |
| Out[2]: __main__.A |