require list comprehensions to start with a for clause

diff --git a/Doc/ref/ref5.tex b/Doc/ref/ref5.tex
index 1abc6cb021d7bbedf454f93e6ff42d0ad574cae6..f6d3b9cd9f3c29278949b9aaefca29f87ad0b850 100644 (file)
--- a/Doc/ref/ref5.tex
+++ b/Doc/ref/ref5.tex
@@ -153,7 +153,7 @@ square brackets:
 
 \begin{verbatim}
 list_display:   "[" [listmaker] "]"
-listmaker:   expression ( list_iter | ( "," expression)* [","] )
+listmaker:   expression ( list_for | ( "," expression)* [","] )
 list_iter:   list_for | list_if
 list_for:    "for" expression_list "in" testlist [list_iter]
 list_if:     "if" test [list_iter]
@@ -164,7 +164,8 @@ 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
+single expression followed by at least one "for" clause and zero 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

diff --git a/Doc/tut/tut.tex b/Doc/tut/tut.tex
index 6451e2a98fe0cf7a309f81181adfabc483eda74a..c5a9294c6720e8d22290dfbca7d94ba947863ef8 100644 (file)
--- a/Doc/tut/tut.tex
+++ b/Doc/tut/tut.tex
@@ -1755,10 +1755,15 @@ item, then to the result and the next item, and so on.  For example,
 
 \subsection{List Comprehensions}
 
-List comprehensions provide a concise way to create lists without
-resorting to use of the \function{map()} or \function{filter()}
-functions.  The resulting construct tends often to be clearer than use
-of those functions.
+List comprehensions provide a concise way to create lists without resorting
+to use of \function{map()}, \function{filter()} and/or \keyword{lambda}.
+The resulting list definition tends often to be clearer than lists built
+using those constructs.  Each list comprehension consists of an expression
+following by a \keyword{for} clause, then zero or more \keyword{for} or
+\keyword{if} clauses.  The result will be a list resulting from evaluating
+the expression in the context of the \keyword{for} and \keyword{if} clauses
+which follow it.  If the expression would evaluate to a tuple, it must be
+parenthesized.
 
 \begin{verbatim}
 >>> freshfruit = ['  banana', '  loganberry ', 'passion fruit  ']
@@ -1771,6 +1776,17 @@ of those functions.
 [12, 18]
 >>> [3*x for x in vec if x < 2]
 []
+>>> [{x: x**2} for x in vec]
+[{2: 4}, {4: 16}, {6: 36}]
+>>> [[x,x**2] for x in vec]
+[[2, 4], [4, 16], [6, 36]]
+>>> [x, x**2 for x in vec]     # error - parens required for tuples
+  File "<stdin>", line 1
+    [x, x**2 for x in vec]
+               ^
+SyntaxError: invalid syntax
+>>> [(x, x**2) for x in vec]
+[(2, 4), (4, 16), (6, 36)]
 >>> vec1 = [2, 4, 6]
 >>> vec2 = [4, 3, -9]
 >>> [x*y for x in vec1 for y in vec2]

diff --git a/Grammar/Grammar b/Grammar/Grammar
index f95923d413801a70ec43b7dfd4283f5a16bcea16..dd12b6d5832fb44b2f53313cfe60b0caabd2eb4e 100644 (file)
--- a/Grammar/Grammar
+++ b/Grammar/Grammar
@@ -77,7 +77,7 @@ term: factor (('*'|'/'|'%') factor)*
 factor: ('+'|'-'|'~') factor | power
 power: atom trailer* ('**' factor)*
 atom: '(' [testlist] ')' | '[' [listmaker] ']' | '{' [dictmaker] '}' | '`' testlist '`' | NAME | NUMBER | STRING+
-listmaker: test ( list_iter | (',' test)* [','] )
+listmaker: test ( list_for | (',' test)* [','] )
 lambdef: 'lambda' [varargslist] ':' test
 trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']

diff --git a/Lib/test/output/test_grammar b/Lib/test/output/test_grammar
index 203cf18774209448272d134c36302ece9eeaabad..8a0c5313b002a2ccb6553c5dfa1e6f0e82c89cc0 100644 (file)
--- a/Lib/test/output/test_grammar
+++ b/Lib/test/output/test_grammar
@@ -55,4 +55,5 @@ classdef
 [(1, 'Apple'), (1, 'Banana'), (1, 'Coconut'), (2, 'Apple'), (2, 'Banana'), (2, 'Coconut'), (3, 'Apple'), (3, 'Banana'), (3, 'Coconut'), (4, 'Apple'), (4, 'Banana'), (4, 'Coconut'), (5, 'Apple'), (5, 'Banana'), (5, 'Coconut')]
 [(1, 'Banana'), (1, 'Coconut'), (2, 'Banana'), (2, 'Coconut'), (3, 'Banana'), (3, 'Coconut'), (4, 'Banana'), (4, 'Coconut'), (5, 'Banana'), (5, 'Coconut')]
 good: got a SyntaxError as expected
+good: got a SyntaxError as expected
 [('Boeing', 'Airliner'), ('Boeing', 'Engine'), ('Ford', 'Engine'), ('Macdonalds', 'Cheeseburger')]

diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index da74444d416fc048851a7b8a2b9b2b2048839efa..b0e3da93057b20db75e584a26c9c519114d9c323 100644 (file)
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -578,6 +578,12 @@ try:
 except SyntaxError:
     print "good: got a SyntaxError as expected"
 
+try:
+    eval("[x if y]")
+    print "FAIL: should have raised a SyntaxError!"
+except SyntaxError:
+        print "good: got a SyntaxError as expected"
+
 suppliers = [
   (1, "Boeing"),
   (2, "Ford"),

diff --git a/Python/compile.c b/Python/compile.c
index e09204e46ab23c01a7af4d1a8f400551e8fae57f..f239bb6a8b70e9cd91009023a52e5367359ef5e5 100644 (file)
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -1043,7 +1043,7 @@ com_list_iter(struct compiling *c,
 static void
 com_list_comprehension(struct compiling *c, node *n)
 {
-       /* listmaker: test list_iter */
+       /* listmaker: test list_for */
        char tmpname[12];
        sprintf(tmpname, "__%d__", ++c->c_tmpname);
        com_addoparg(c, BUILD_LIST, 0);
@@ -1052,7 +1052,7 @@ com_list_comprehension(struct compiling *c, node *n)
        com_addopnamestr(c, LOAD_ATTR, "append");
        com_addopnamestr(c, STORE_NAME, tmpname);
        com_pop(c, 1);
-       com_list_iter(c, n, CHILD(n, 0), tmpname);
+       com_list_for(c, CHILD(n, 1), CHILD(n, 0), tmpname);
        com_addopnamestr(c, DELETE_NAME, tmpname);
        --c->c_tmpname;
 }
@@ -1060,8 +1060,8 @@ com_list_comprehension(struct compiling *c, node *n)
 static void
 com_listmaker(struct compiling *c, node *n)
 {
-       /* listmaker: test ( list_iter | (',' test)* [','] ) */
-       if (NCH(n) > 1 && TYPE(CHILD(n, 1)) == list_iter)
+       /* listmaker: test ( list_for | (',' test)* [','] ) */
+       if (NCH(n) > 1 && TYPE(CHILD(n, 1)) == list_for)
                com_list_comprehension(c, n);
        else {
                int len = 0;

diff --git a/Python/graminit.c b/Python/graminit.c
index a62b62e32ef42533a5f8554c71b15b8d4695cd78..c8570ff6e1242f2245cf5bb26f5dc19c9066f148 100644 (file)
--- a/Python/graminit.c
+++ b/Python/graminit.c
@@ -1317,7 +1317,7 @@ static state states_59[4] = {
        {1, arcs_59_3},
 };
 static arc arcs_60_0[2] = {
-       {128, 1},
+       {120, 1},
        {129, 1},
 };
 static arc arcs_60_1[1] = {
@@ -1340,7 +1340,7 @@ static arc arcs_61_3[1] = {
        {9, 4},
 };
 static arc arcs_61_4[2] = {
-       {120, 5},
+       {128, 5},
        {0, 4},
 };
 static arc arcs_61_5[1] = {
@@ -1361,7 +1361,7 @@ static arc arcs_62_1[1] = {
        {21, 2},
 };
 static arc arcs_62_2[2] = {
-       {120, 3},
+       {128, 3},
        {0, 2},
 };
 static arc arcs_62_3[1] = {
@@ -1622,7 +1622,7 @@ static label labels[130] = {
        {25, 0},
        {2, 0},
        {3, 0},
-       {316, 0},
+       {317, 0},
        {1, "lambda"},
        {314, 0},
        {307, 0},
@@ -1630,7 +1630,7 @@ static label labels[130] = {
        {309, 0},
        {1, "class"},
        {315, 0},
-       {317, 0},
+       {316, 0},
        {318, 0},
 };
 grammar _PyParser_Grammar = {