New submission from Richard Decal <richard.de...@gmail.com>:
In brief:
```
from collections import Counter
x = Counter({'a': 0, 'b': 1})
x.update(x) # works: Counter({'a': 0, 'b': 2})
x += x # expected: Counter({'a': 0, 'b': 3}) actual: Counter({'b': 3})
```
I expect `+=` and `.update()` to be synonymous. However, the += operator is
deleting keys if the source Counter has a zero count to begin with:
```
x = Counter({'a': 1})
x += Counter({'a': 0}) # ok: Counter({'a': 1})
y = Counter({'a': 0})
y += y # expected: Counter({'a': 0}) actual: Counter()
```
----------
messages: 407348
nosy: crypdick
priority: normal
severity: normal
status: open
title: collections.Counter drops key if value is 0 and updating using +=
operator
type: behavior
versions: Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue45936>
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