gh-81263: Add assignment expressions to `help` (#124641)

* Add assignment expression (:=) to `help`

* Update index for Assignment Expressions to include pair of `assignment; expression`

1 files changed, 28 insertions, 0 deletions

diff --git a/Lib/pydoc_data/topics.py b/Lib/pydoc_data/topics.py
index 4643df8..97bb4eb 100644
--- a/Lib/pydoc_data/topics.py
+++ b/Lib/pydoc_data/topics.py
@@ -416,6 +416,34 @@ topics = {'assert': 'The "assert" statement\n'
                'some expressions (like un-parenthesized tuple expressions) '
                'caused a\n'
                'syntax error.\n',
+ 'assignment-expressions': 'Assignment expressions\n'
+          '**********************\n'
+          '\n'
+          'An assignment expression (sometimes also called a “named expression”'
+          '\nor “walrus”) assigns an expression to an identifier, while also\n'
+          'returning the value of the expression.\n'
+          '\n'
+          'One common use case is when handling matched regular expressions:\n'
+          '\n'
+          '   if matching := pattern.search(data):\n'
+          '      do_something(matching)\n'
+          '\n'
+          'Or, when processing a file stream in chunks:\n'
+          '\n'
+          '   while chunk := file.read(9000):\n'
+          '      process(chunk)\n'
+          '\n'
+          'Assignment expressions must be surrounded by parentheses when used as\n'
+          'expression statements and when used as sub-expressions in slicing,\n'
+          'conditional, lambda, keyword-argument, and comprehension-if\n'
+          'expressions and in assert, with, and assignment statements. In all\n'
+          'other places where they can be used, parentheses are not required,\n'
+          'including in if and while statements.\n'
+          '\n'
+          'Added in version 3.8.\n'
+          'See also:\n'
+          '\n'
+          '  **PEP 572** - Assignment Expressions\n',
  'async': 'Coroutines\n'
           '**********\n'
           '\n'