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bpo-39868: Update Language Reference for PEP 572. #18793

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Merged
merged 8 commits into from
Mar 6, 2020
Merged

bpo-39868: Update Language Reference for PEP 572. #18793

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ecddd10
Add PEP 572 grammar docs to the Language Reference.
brandtbucher Mar 6, 2020
c39c071
Update comment.
brandtbucher Mar 6, 2020
7377e52
NEWS.
brandtbucher Mar 6, 2020
04c9445
Update documented comprehension grammar.
brandtbucher Mar 6, 2020
6a0f640
Fix corner cases from PEP 572.
brandtbucher Mar 6, 2020
d5bb4a7
Remove stray line.
brandtbucher Mar 6, 2020
da3bc53
Fix bad copy-paste.
brandtbucher Mar 6, 2020
91d8f4d
Don't allow complex identifiers.
brandtbucher Mar 6, 2020
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6 changes: 3 additions & 3 deletions Doc/reference/compound_stmts.rst
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Expand Up @@ -90,8 +90,8 @@ The :keyword:`!if` statement
The :keyword:`if` statement is used for conditional execution:

.. productionlist::
if_stmt: "if" `expression` ":" `suite`
: ("elif" `expression` ":" `suite`)*
if_stmt: "if" `assignment_expression` ":" `suite`
: ("elif" `assignment_expression` ":" `suite`)*
: ["else" ":" `suite`]

It selects exactly one of the suites by evaluating the expressions one by one
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Do you think "expression" here needs updating too? It becomes a bit ugly that way, and in context it doesn't seem ambiguous.

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(I thought more about it and I don't think it needs updating, so I'll land now.)

Expand All @@ -116,7 +116,7 @@ The :keyword:`while` statement is used for repeated execution as long as an
expression is true:

.. productionlist::
while_stmt: "while" `expression` ":" `suite`
while_stmt: "while" `assignment_expression` ":" `suite`
: ["else" ":" `suite`]

This repeatedly tests the expression and, if it is true, executes the first
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18 changes: 15 additions & 3 deletions Doc/reference/expressions.rst
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Expand Up @@ -178,7 +178,7 @@ called "displays", each of them in two flavors:
Common syntax elements for comprehensions are:

.. productionlist::
comprehension: `expression` `comp_for`
comprehension: `assignment_expression` `comp_for`
comp_for: ["async"] "for" `target_list` "in" `or_test` [`comp_iter`]
comp_iter: `comp_for` | `comp_if`
comp_if: "if" `expression_nocond` [`comp_iter`]
Expand Down Expand Up @@ -911,7 +911,8 @@ series of :term:`arguments <argument>`:
: ["," `keywords_arguments`]
: | `starred_and_keywords` ["," `keywords_arguments`]
: | `keywords_arguments`
positional_arguments: ["*"] `expression` ("," ["*"] `expression`)*
positional_arguments: positional_item ("," positional_item)*
positional_item: `assignment_expression` | "*" `expression`
starred_and_keywords: ("*" `expression` | `keyword_item`)
: ("," "*" `expression` | "," `keyword_item`)*
keywords_arguments: (`keyword_item` | "**" `expression`)
Expand Down Expand Up @@ -1642,6 +1643,17 @@ returns a boolean value regardless of the type of its argument
(for example, ``not 'foo'`` produces ``False`` rather than ``''``.)


Assignment expressions
======================

.. productionlist::
assignment_expression: [`identifier` ":="] `expression`

.. TODO: BPO-39868

See :pep:`572` for more details about assignment expressions.


.. _if_expr:

Conditional expressions
Expand Down Expand Up @@ -1711,7 +1723,7 @@ Expression lists
expression_list: `expression` ("," `expression`)* [","]
starred_list: `starred_item` ("," `starred_item`)* [","]
starred_expression: `expression` | (`starred_item` ",")* [`starred_item`]
starred_item: `expression` | "*" `or_expr`
starred_item: `assignment_expression` | "*" `or_expr`

.. index:: object: tuple

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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Documentation/2020-03-05-16-29-03.bpo-39868.JQoHhO.rst
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@@ -0,0 +1 @@
Updated the Language Reference for :pep:`572`.