Weakref proxy missing pass throughs for hash() and reversed()

[rhettinger]

BPO	40523
Nosy	@rhettinger, @pablogsal
PRs	bpo-40523: Add pass-throughs for hash() and reversed() to weakref.proxy objects #19946

^{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 2020-05-05.21:58:36.117>
created_at = <Date 2020-05-05.18:34:38.699>
labels = ['3.8', 'type-bug', 'library', '3.9']
title = 'Weakref proxy missing pass throughs for hash() and reversed()'
updated_at = <Date 2020-05-05.21:58:36.116>
user = 'https://github.com/rhettinger'

bugs.python.org fields:

activity = <Date 2020-05-05.21:58:36.116>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2020-05-05.21:58:36.117>
closer = 'pablogsal'
components = ['Library (Lib)']
creation = <Date 2020-05-05.18:34:38.699>
creator = 'rhettinger'
dependencies = []
files = []
hgrepos = []
issue_num = 40523
keywords = ['patch']
message_count = 2.0
messages = ['368197', '368211']
nosy_count = 2.0
nosy_names = ['rhettinger', 'pablogsal']
pr_nums = ['19946']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue40523'
versions = ['Python 3.8', 'Python 3.9']

[rhettinger]

from weakref import proxy

class Alpha:
    def __len__(self):
        return 3
    def __reversed__(self):
        return iter('cba')
    def __hash__(self):
        return hash('abc')

a = Alpha()

# Direct use of the instance works
print(len(a))
print(list(reversed(a)))
print(hash(a))

# Proxies can use the dunder methods directly
r = proxy(a)
print(r.__len__())
print(list(r.__reversed__()))
print(r.__hash__())

# Proxy fails for __reversed__ and __hash__
print(len(r), 'This succeeds')
try:
print(list(reversed(r)))
except TypeError:
print('reverse(r) failed')
try:
print(hash(r))
except TypeError:
print('hash(r) failed')

[pablogsal]

New changeset 96074de by Pablo Galindo in branch 'master':
bpo-40523: Add pass-throughs for hash() and reversed() to weakref.proxy objects (GH-19946)
96074de