list comprehensions. see

    http://sourceforge.net/patch/?func=detailpatch&patch_id=100654&group_id=5470

for details.

2 files changed, 35 insertions, 5 deletions

diff --git a/Doc/ref/ref5.tex b/Doc/ref/ref5.tex
index db98fe4..6b699bc 100644
--- a/Doc/ref/ref5.tex
+++ b/Doc/ref/ref5.tex
@@ -152,13 +152,22 @@ A list display is a possibly empty series of expressions enclosed in
 square brackets:
 
 \begin{verbatim}
-list_display:   "[" [expression_list] "]"
+list_display:   "[" [expression_list [list_iter]] "]"
+list_iter:   list_for | list_if
+list_for:    "for" expression_list "in" testlist [list_iter]
+list_if:     "if" test [list_iter]
 \end{verbatim}
 
-A list display yields a new list object.  If it has no expression
-list, the list object has no items.  Otherwise, the elements of the
-expression list are evaluated from left to right and inserted in the
-list object in that order.
+A list display yields a new list object.  Its contents are specified
+by providing either a list of expressions or a list comprehension.
+When a comma-separated list of expressions is supplied, its elements are
+evaluated from left to right and placed into the list object in that
+order.  When a list comprehension is supplied, it consists of a
+single expression followed by one or more "for" or "if" clauses.  In this
+case, the elements of the new list are those that would be produced
+by considering each of the "for" or "if" clauses a block, nesting from
+left to right, and evaluating the expression to produce a list element
+each time the innermost block is reached.
 \obindex{list}
 \indexii{empty}{list}
 
diff --git a/Doc/tut/tut.tex b/Doc/tut/tut.tex
index b53d6ea..f811932 100644
--- a/Doc/tut/tut.tex
+++ b/Doc/tut/tut.tex
@@ -1753,6 +1753,27 @@ item, then to the result and the next item, and so on.  For example,
 0
 \end{verbatim}
 
+\subsection{List Comprehensions}
+
+List comprehensions provide a concise way to create lists without resorting
+to use of the \func{map()} or \func{filter()} functions.  The resulting
+construct tends often to be clearer than use of those functions.
+
+\begin{verbatim}
+>>> spcs = ["  Apple", " Banana ", "Coco  nut  "]
+>>> print [s.strip() for s in spcs]
+['Apple', 'Banana', 'Coco  nut']
+>>> vec = [2, 4, 6]
+>>> print [3*x for x in vec]
+[6, 12, 18]
+>>> vec1 = [2, 4, 6]
+>>> vec2 = [4, 3, -9]
+>>> print [x*y for x in vec1 for y in vec2]
+[8, 6, -18, 16, 12, -36, 24, 18, -54]
+>>> print [x+y for x in vec1 for y in vec2]
+[6, 5, -7, 8, 7, -5, 10, 9, -3]
+\end{verbatim}
+
 \section{The \keyword{del} statement \label{del}}
 
 There is a way to remove an item from a list given its index instead