fix yaml construct a slot object

[Hanaasagi]

Env:

• Python 3.7
• pyyaml master branch

Test code:

import yaml


class A:
    __slots__ = ('c',)

    def __init__(self):
        self.c = 3


data = yaml.dump({'a': A()})
d = yaml.load(data)

Trackback:

Traceback (most recent call last):
  File "t.py", line 12, in <module>
    d = yaml.load(data)
  File "/root/py36/lib/python3.7/site-packages/yaml/__init__.py", line 72, in load
    return loader.get_single_data()
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 37, in get_single_data
    return self.construct_document(node)
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 46, in construct_document
    for dummy in generator:
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 398, in construct_yaml_map
    value = self.construct_mapping(node)
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 204, in construct_mapping
    return super().construct_mapping(node, deep=deep)
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 129, in construct_mapping
    value = self.construct_object(value_node, deep=deep)
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 88, in construct_object
    data = constructor(self, tag_suffix, node)
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 617, in construct_python_object_new
    return self.construct_python_object_apply(suffix, node, newobj=True)
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 608, in construct_python_object_apply
    self.set_python_instance_state(instance, state)
  File "/root/py36/lib/python3.7/site-packages/yaml/constructor.py", line 570, in set_python_instance_state
    setattr(object, key, value)
TypeError: can't set attributes of built-in/extension type 'object'

The exception was throwed from #L570

pyyaml/lib3/yaml/constructor.py

Lines 558 to 570 in ccc40f3

	def set_python_instance_state(self, instance, state):
	if hasattr(instance, '__setstate__'):
	instance.__setstate__(state)
	else:
	slotstate = {}
	if isinstance(state, tuple) and len(state) == 2:
	state, slotstate = state
	if hasattr(instance, '__dict__'):
	instance.__dict__.update(state)
	elif state:
	slotstate.update(state)
	for key, value in slotstate.items():
	setattr(object, key, value)

I think object should be instance.

[Hanaasagi]

resolves #232

[Hanaasagi]

This PR has been open for a week. Can I get a review? @ingydotnet

[Hanaasagi]

ping @perlpunk

[perlpunk]

Sorry, I don't know enough python yet, so I don't know about slots. @nitzmahone maybe?

[MRigal]

Very valid fix and proper tests! However, it is just a minimal update to the already exising PR #161 which you could have mentioned.

@perlpunk This is definitely good code and a problem since a while!

[Hanaasagi]

May I get a review @nitzmahone

[paulgmiller]

Hit this same thing and made the same fix locally. Not sure if anyone will approve if this is full loader is deprecated though.

[perlpunk]

Thanks! I'll try to look at it this weekend...

[perlpunk]

Yep, looks good (after I read about what slots are)!

[perlpunk]

I added #161 to release/5.3

[perlpunk]

released https://pypi.org/project/PyYAML/5.3/