ChainMap.keys() is broken

[Zaharid]

BPO	27399
Nosy	@rhettinger, @Zaharid

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2016-06-27.11:13:00.243>
created_at = <Date 2016-06-27.11:07:45.246>
labels = ['invalid', 'library']
title = 'ChainMap.keys() is broken'
updated_at = <Date 2016-06-27.13:30:35.459>
user = 'https://github.com/Zaharid'

bugs.python.org fields:

activity = <Date 2016-06-27.13:30:35.459>
actor = 'r.david.murray'
assignee = 'none'
closed = True
closed_date = <Date 2016-06-27.11:13:00.243>
closer = 'Zahari.Dim'
components = ['Library (Lib)']
creation = <Date 2016-06-27.11:07:45.246>
creator = 'Zahari.Dim'
dependencies = []
files = []
hgrepos = []
issue_num = 27399
keywords = []
message_count = 1.0
messages = ['269370']
nosy_count = 2.0
nosy_names = ['rhettinger', 'Zahari.Dim']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue27399'
versions = ['Python 3.5']

[Zaharid]

When trying to see if the keys() of a collections.ChainMap object are empty, it tries to compute the hash of the dicts that compose the ChainMap, giving rise to an error:

In [1]: from collections import ChainMap

In [2]: m = ChainMap([{'a':1}, {'b':2}])

In [3]: bool(m.keys())
---------------------------------------------------------------------------

TypeError                                 Traceback (most recent call last)
<ipython-input-3-365f7b817ebf> in <module>()
----> 1 bool(m.keys())

/home/zah/anaconda3/lib/python3.5/collections_abc.py in __len_(self)
633
634 def __len__(self):
--> 635 return len(self._mapping)
636
637 def __repr__(self):

/home/zah/anaconda3/lib/python3.5/collections/init.py in __len__(self)
865
866 def __len__(self):
--> 867 return len(set().union(*self.maps)) # reuses stored hash values if possible
868
869 def __iter__(self):

TypeError: unhashable type: 'dict'

Also, I can't ask if 'a' is in keys:

In [6]: m.keys()
Out[6]: KeysView(ChainMap([{'a': 1}, {'b': 2}]))
In [9]: ks = m.keys()
In [17]: 'a' in ks
Out[17]: False