bpo-39868: Update Language Reference for PEP 572. (GH-18793)

(cherry picked from commit 8bae219)

Co-authored-by: Brandt Bucher <[email protected]>

Author: miss-islington

Doc/reference/compound_stmts.rst

@@ -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
@@ -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

Doc/reference/expressions.rst

@@ -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`]
@@ -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`)
@@ -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
@@ -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
 

Misc/NEWS.d/next/Documentation/2020-03-05-16-29-03.bpo-39868.JQoHhO.rst

@@ -0,0 +1 @@
+Updated the Language Reference for :pep:`572`.