下面是asdict的CPython实现
– 或者具体来说，它使用的内部递归辅助函数_asdict_inner：
# Source: https://github.com/python/cpython/blob/master/Lib/dataclasses.py
def _asdict_inner(obj, dict_factory):
if _is_dataclass_instance(obj):
result = []
for f in fields(obj):
value = _asdict_inner(getattr(obj, f.name), dict_factory)
result.append((f.name, value))
return dict_factory(result)
elif isinstance(obj, tuple) and hasattr(obj, '_fields'):
# [large block of author comments]
return type(obj)(*[_asdict_inner(v, dict_factory) for v in obj])
elif isinstance(obj, (list, tuple)):
# [ditto]
return type(obj)(_asdict_inner(v, dict_factory) for v in obj)
elif isinstance(obj, dict):
return type(obj)((_asdict_inner(k, dict_factory),
_asdict_inner(v, dict_factory))
for k, v in obj.items())
else:
return copy.deepcopy(obj)
asdict 只是用一些断言调用上面的方法，默认情况下是dict_factory=dict。
如何调整它以创建具有所需类型标记的输出字典，如 cmets 中所述？
1.添加类型信息
我的尝试涉及创建一个继承自 dict 的自定义返回包装器：
class TypeDict(dict):
def __init__(self, t, *args, **kwargs):
super(TypeDict, self).__init__(*args, **kwargs)
if not isinstance(t, type):
raise TypeError("t must be a type")
self._type = t
@property
def type(self):
return self._type
查看原始代码，只需要修改第一个子句即可使用此包装器，因为其他子句仅处理dataclass-es的containers：
# only use dict for now; easy to add back later
def _todict_inner(obj):
if is_dataclass_instance(obj):
result = []
for f in fields(obj):
value = _todict_inner(getattr(obj, f.name))
result.append((f.name, value))
return TypeDict(type(obj), result)
elif isinstance(obj, tuple) and hasattr(obj, '_fields'):
return type(obj)(*[_todict_inner(v) for v in obj])
elif isinstance(obj, (list, tuple)):
return type(obj)(_todict_inner(v) for v in obj)
elif isinstance(obj, dict):
return type(obj)((_todict_inner(k), _todict_inner(v))
for k, v in obj.items())
else:
return copy.deepcopy(obj)
进口：
from dataclasses import dataclass, fields, is_dataclass
# thanks to Patrick Haugh
from typing import *
# deepcopy
import copy
使用的功能：
# copy of the internal function _is_dataclass_instance
def is_dataclass_instance(obj):
return is_dataclass(obj) and not is_dataclass(obj.type)
# the adapted version of asdict
def todict(obj):
if not is_dataclass_instance(obj):
raise TypeError("todict() should be called on dataclass instances")
return _todict_inner(obj)
使用示例数据类进行测试：
c = C([Point(0, 0), Point(10, 4)])
print(c)
cd = todict(c)
print(cd)
# {'mylist': [{'x': 0, 'y': 0}, {'x': 10, 'y': 4}]}
print(cd.type)
# <class '__main__.C'>
结果符合预期。
2。转换回dataclass
asdict 使用的递归例程可以重新用于反向过程，只需进行一些相对较小的更改：
def _fromdict_inner(obj):
# reconstruct the dataclass using the type tag
if is_dataclass_dict(obj):
result = {}
for name, data in obj.items():
result[name] = _fromdict_inner(data)
return obj.type(**result)
# exactly the same as before (without the tuple clause)
elif isinstance(obj, (list, tuple)):
return type(obj)(_fromdict_inner(v) for v in obj)
elif isinstance(obj, dict):
return type(obj)((_fromdict_inner(k), _fromdict_inner(v))
for k, v in obj.items())
else:
return copy.deepcopy(obj)
使用的功能：
def is_dataclass_dict(obj):
return isinstance(obj, TypeDict)
def fromdict(obj):
if not is_dataclass_dict(obj):
raise TypeError("fromdict() should be called on TypeDict instances")
return _fromdict_inner(obj)
测试：
c = C([Point(0, 0), Point(10, 4)])
cd = todict(c)
cf = fromdict(cd)
print(c)
# C(mylist=[Point(x=0, y=0), Point(x=10, y=4)])
print(cf)
# C(mylist=[Point(x=0, y=0), Point(x=10, y=4)])
又如预期的那样。