[New-bugs-announce] [issue27576] An unexpected difference between dict and OrderedDict

[Alexander Belopolsky]

New submission from Alexander Belopolsky:

Consider the following code:

$ cat x.py
from collections import OrderedDict
class X:
    def items(self):
        print('items')
        return []
    def keys(self):
        print('keys')
        return []

print(dict(X()))
print(OrderedDict(X()))

When I run it under python 3.4, I get

$ python3.4 x.py
keys
{}
keys
OrderedDict()

but under python 3.5, I get

$ python3.5 x.py
keys
{}
items
OrderedDict()


Under 3.4 both dict and OrderedDict constructors call the keys() method of the underlying object (and then call __getitem__ repeatedly if keys() returns a non-empty list), but in 3.5 OrderedDict behavior changed and it calls the values() method instead.

----------
keywords: 3.4regression
messages: 270842
nosy: belopolsky
priority: normal
severity: normal
status: open
title: An unexpected difference between dict and OrderedDict
type: behavior
versions: Python 3.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27576>
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