collections.Counter, when empty, doesn't raise an error with &= when other is an incompatible type

[ethanfurman]

BPO	22801
Nosy	@rhettinger, @ethanfurman, @serhiy-storchaka
Files	issue22801.stoneleaf.01.patch

^{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 = 'https://github.com/rhettinger'
closed_at = <Date 2015-03-03.05:33:53.308>
created_at = <Date 2014-11-05.17:44:31.739>
labels = ['type-bug']
title = "collections.Counter, when empty, doesn't raise an error with &= when other is an incompatible type"
updated_at = <Date 2015-03-03.05:33:53.307>
user = 'https://github.com/ethanfurman'

bugs.python.org fields:

activity = <Date 2015-03-03.05:33:53.307>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2015-03-03.05:33:53.308>
closer = 'rhettinger'
components = []
creation = <Date 2014-11-05.17:44:31.739>
creator = 'ethan.furman'
dependencies = []
files = ['37137']
hgrepos = []
issue_num = 22801
keywords = ['patch']
message_count = 3.0
messages = ['230699', '237035', '237107']
nosy_count = 3.0
nosy_names = ['rhettinger', 'ethan.furman', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'test needed'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue22801'
versions = ['Python 3.4', 'Python 3.5']

[ethanfurman]

test script:
---------------------------------------

from collections import Counter
empty_counter = Counter()
counter = Counter('abbc')
empty_counter &= 5
counter &= 5

---

results:
---------------------------------------

Traceback (most recent call last):
  File "blah.py", line 5, in <module>
    counter &= 5
  File "/home/ethan/source/python/issue22778/Lib/collections/__init__.py", line 780, in __iand__
    other_count = other[elem]
TypeError: 'int' object is not subscriptable

---

As can be seen, the error does not show up when the Counter is empty, which could lead to hard to diagnose bugs.

[serhiy-storchaka]

Additional check is not for free.

$ ./python -m timeit -s "from collections import Counter; a = Counter(); b = Counter(range(10))" -- "a &= b"

Unpatched: 100000 loops, best of 3: 8.4 usec per loop
Patched: 100000 loops, best of 3: 9.7 usec per loop

[rhettinger]

I see no reason pure python code to have to detect and report such oddities.
Closing as not worth it.