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Merged
rhettinger merged 12 commits into from
Aug 12, 2019
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bpo-37759: Second round of edits to Whatsnew 3.8 #15204

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3b9e09b
Add examples for dict evaluation order
rhettinger Aug 11, 2019
4138137
Add test set up
rhettinger Aug 11, 2019
6a25e5a
Explain the replace() method for code objects.
rhettinger Aug 11, 2019
f9f511e
Remove stray character
rhettinger Aug 11, 2019
6099153
Edit the entry on the missing comma SyntaxWarning
rhettinger Aug 11, 2019
838d143
Syntax change for iterable unpacking in yield/return statements
rhettinger Aug 11, 2019
b325ff7
We're no longer on Mercurial
rhettinger Aug 11, 2019
8a91d0f
Rationale for as_integer_ratio() on int and bool
rhettinger Aug 11, 2019
2392249
Update for Fraction.as_integer_ratio()
rhettinger Aug 11, 2019
5290bfd
Demonstrate the importlib.metadata package
rhettinger Aug 11, 2019
fa7a9c9
Fix typo
rhettinger Aug 12, 2019
310ddfb
PEP 8 nit
rhettinger Aug 12, 2019
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Add examples for dict evaluation order
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@rhettinger
rhettinger committed Aug 11, 2019
commit 3b9e09b527998437834054d624ba37cb4dca7798
26 changes: 24 additions & 2 deletions Doc/whatsnew/3.8.rst
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Expand Up @@ -468,8 +468,30 @@ Other Language Changes

(Contributed by Mark Dickinson in :issue:`36027`.)

* When dictionary comprehensions are evaluated, the key is now evaluated before
the value, as proposed by :pep:`572`.
* Dict comprehensions have been synced-up with dict literals so that the
key is computed first and the value second::

>>> # Dict comprehension
>>> cast = {input('role? '): input('actor? ') for i in range(2)}
role? King Arthur
actor? Chapman
role? Black Knight
actor? Cleese

>>> # Dict literal
>>> cast = {input('role? '): input('actor? ')}
role? Sir Robin
actor? Eric Idle

The guaranteed execution order is helpful with assignment expressions
because variables assigned in the key expression will be available in
the value expression::

>>> names = ['Martin von Löwis', 'Łukasz Langa', 'Walter Dörwald']
>>> {(n := normalize('NFC', name)).casefold() : n for name in names}
{'martin von löwis': 'Martin von Löwis',
'łukasz langa': 'Łukasz Langa',
'walter dörwald': 'Walter Dörwald'}


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