[Python-checkins] r78772 - python/trunk/Doc/reference/expressions.rst

[georg.brandl]

Author: georg.brandl
Date: Sun Mar  7 22:12:28 2010
New Revision: 78772

Log:
#8039: document conditional expressions better, giving them their own section.

Modified:
   python/trunk/Doc/reference/expressions.rst

Modified: python/trunk/Doc/reference/expressions.rst
==============================================================================
--- python/trunk/Doc/reference/expressions.rst	(original)
+++ python/trunk/Doc/reference/expressions.rst	Sun Mar  7 22:12:28 2010
@@ -185,6 +185,7 @@
    list_comprehension: `expression` `list_for`
    list_for: "for" `target_list` "in" `old_expression_list` [`list_iter`]
    old_expression_list: `old_expression` [("," `old_expression`)+ [","]]
+   old_expression: `or_test` | `old_lambda_form`
    list_iter: `list_for` | `list_if`
    list_if: "if" `old_expression` [`list_iter`]
 
@@ -1186,12 +1187,7 @@
    pair: Conditional; expression
    pair: Boolean; operation
 
-Boolean operations have the lowest priority of all Python operations:
-
 .. productionlist::
-   expression: `conditional_expression` | `lambda_form`
-   old_expression: `or_test` | `old_lambda_form`
-   conditional_expression: `or_test` ["if" `or_test` "else" `expression`]
    or_test: `and_test` | `or_test` "or" `and_test`
    and_test: `not_test` | `and_test` "and" `not_test`
    not_test: `comparison` | "not" `not_test`
@@ -1208,12 +1204,6 @@
 The operator :keyword:`not` yields ``True`` if its argument is false, ``False``
 otherwise.
 
-The expression ``x if C else y`` first evaluates *C* (*not* *x*); if *C* is
-true, *x* is evaluated and its value is returned; otherwise, *y* is evaluated
-and its value is returned.
-
-.. versionadded:: 2.5
-
 .. index:: operator: and
 
 The expression ``x and y`` first evaluates *x*; if *x* is false, its value is
@@ -1233,6 +1223,29 @@
 'foo'`` yields ``False``, not ``''``.)
 
 
+Conditional Expressions
+=======================
+
+.. versionadded:: 2.5
+
+.. index::
+   pair: conditional; expression
+   pair: ternary; operator
+
+.. productionlist::
+   conditional_expression: `or_test` ["if" `or_test` "else" `expression`]
+   expression: `conditional_expression` | `lambda_form`
+
+Conditional expressions (sometimes called a "ternary operator") have the lowest
+priority of all Python operations.
+
+The expression ``x if C else y`` first evaluates the condition, *C* (*not* *a*);
+if *C* is true, *x* is evaluated and its value is returned; otherwise, *y* is
+evaluated and its value is returned.
+
+See :pep:`308` for more details about conditional expressions.
+
+
 .. _lambdas:
 .. _lambda:
 
@@ -1326,6 +1339,8 @@
 +===============================================+=====================================+
 | :keyword:`lambda`                             | Lambda expression                   |
 +-----------------------------------------------+-------------------------------------+
+| :keyword:`if` -- :keyword:`else`              | Conditional expression              |
++-----------------------------------------------+-------------------------------------+
 | :keyword:`or`                                 | Boolean OR                          |
 +-----------------------------------------------+-------------------------------------+
 | :keyword:`and`                                | Boolean AND                         |