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

Sun Mar 7 22:12:28 CET 2010

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 |
