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[Python-Dev] PEP 572: Assignment Expressions

Chris Angelico rosuav at gmail.com
Sun Apr 22 18:27:42 EDT 2018 
On Mon, Apr 23, 2018 at 8:20 AM, Mike Miller <python-dev at mgmiller.net> wrote:
>
> On 2018-04-22 14:33, Chris Angelico wrote:
>>
>> with open(fn) as f:
>> with (open(fn) as f):
>>
>> These two do the same thing, but only because a file object's
>> __enter__ returns self. So it's dangerous, because it WILL work... and
>> people will get into the habit of parenthesizing to permit a 'with'
>> statement to go across line breaks. And then they'll use a different
>> context manager, like closing(), or a PsycoPG2 database connection (I
>> think), where it returns something else. And it'll work, until they go
>> over multiple lines, and then suddenly the semantics change.
>
>
>
> Why do you think folks will be rushing to parenthesize with statements when
> it has always been a syntax error, there is years of code and docs that show
> otherwise, no use cases, and will take years for 3.8 to trickle out?

Because it's been requested a number of times as a way to allow a
'with' statement to go across lines without backslashes.

If it becomes possible, it will be used.

ChrisA
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