gvanrossum · Jul 25, 2020 · Mar 8, 2020 · Mar 8, 2020 · Mar 10, 2020 · Mar 10, 2020
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst
@@ -1649,7 +1649,61 @@ Assignment expressions
 .. productionlist::
    assignment_expression: [`identifier` ":="] `expression`
 
-.. TODO: BPO-39868
+Assignment expression is the new expression introduced in the Python3.8
+or later (sometimes also called as "named expression" or "walrus operator"),
+which aims to reduce the number of lines of code by allowing the
+assignment and return of value in the same expression. This makes codebase
+more readable and maintainable.
+
+The expression ``name := expr`` where **expr** is any valid Python expression
+other than an unparenthesize tuple and the **name** is an identifier.
+Here the variable **name** holds the assigned value of a given **expression**.
+
-Assignment expression is the new expression introduced in the Python3.8
-or later (sometimes also called as "named expression" or "walrus operator"),
-which aims to reduce the number of lines of code by allowing the
-assignment and return of value in the same expression. This makes codebase
-more readable and maintainable.
-
-The expression ``name := expr`` where **expr** is any valid Python expression
-other than an unparenthesize tuple and the **name** is an identifier.
-Here the variable **name** holds the assigned value of a given **expression**.
+An assignment expression (sometimes also called a "named expression" or
+"walrus") assigns an :token:`expression` to an :token:`identifier`, while also
+returning the value of the :token:`expression`. 
-Assignment expression is the new expression introduced in the Python3.8
-or later (sometimes also called as "named expression" or "walrus operator"),
-which aims to reduce the number of lines of code by allowing the
-assignment and return of value in the same expression. This makes codebase
-more readable and maintainable.
-
-The expression ``name := expr`` where **expr** is any valid Python expression
-other than an unparenthesize tuple and the **name** is an identifier.
-Here the variable **name** holds the assigned value of a given **expression**.
+An assignment expression (sometimes also called a "named expression" or
+"walrus") assigns an :token:`expression` to an :token:`identifier`, while also
+returning the value of the :token:`expression`. 
+**Examples**
+
+*The following examples demonstrate the use case of an assignment expressions.*
+
-
-**Examples**
-
-*The following examples demonstrate the use case of an assignment expressions.*
-
-**Examples**
-
-*The following examples demonstrate the use case of an assignment expressions.*
+
+One common use case is when handling the matched data in regular expression
-One common use case is when handling the matched data in regular expression
+One common use case is when handling matched regular expressions:
-One common use case is when handling the matched data in regular expression
+One common use case is when handling matched regular expressions:
+
+**Current scenario**
+
+.. code-block:: python
+
+   matching = patern.search(data)
+   if matching:
+       do_something(matching)
+
+Notice that a matching variable is being called two times in the code
+that may be replaced using assignment expression in one line.
+
+**Using assignment expression**
-
-**Current scenario**
-
-.. code-block:: python
-
-   matching = patern.search(data)
-   if matching:
-       do_something(matching)
-
-Notice that a matching variable is being called two times in the code
-that may be replaced using assignment expression in one line.
-
-**Using assignment expression**
-
-**Current scenario**
-
-.. code-block:: python
-
-   matching = patern.search(data)
-   if matching:
-       do_something(matching)
-
-Notice that a matching variable is being called two times in the code
-that may be replaced using assignment expression in one line.
-
-**Using assignment expression**
+
+.. code-block:: python
+
+   if (matching := pattern.search(data)):
-   if (matching := pattern.search(data)):
+   if matching := pattern.search(data):
-   if (matching := pattern.search(data)):
+   if matching := pattern.search(data):
+       do_something(matching)
+
+
+Another popular use case is when processing the streams in a
+chunk from the file.
-Another popular use case is when processing the streams in a
-chunk from the file.
+Or, when processing a file stream in chunks:
-Another popular use case is when processing the streams in a
-chunk from the file.
+Or, when processing a file stream in chunks:
+
+**Current scenario**
+
+.. code-block:: python
+
+   chunk = file.read(9000)
+   while chunk:
+       process(chunk)
+       chunk = file.read(9000)
+
+**Using assignment expression**
-
-**Current scenario**
-
-.. code-block:: python
-
-   chunk = file.read(9000)
-   while chunk:
-       process(chunk)
-       chunk = file.read(9000)
-
-**Using assignment expression**
-
-**Current scenario**
-
-.. code-block:: python
-
-   chunk = file.read(9000)
-   while chunk:
-       process(chunk)
-       chunk = file.read(9000)
-
-**Using assignment expression**
+
+.. code-block:: python
+
+   while chunk := file.read(9000):
+       process(chunk)
+
 
 See :pep:`572` for more details about assignment expressions.
 
-
+
+.. versionadded:: 3.8
+
-
+
+.. versionadded:: 3.8
+