SF patch #872326: Generator expression implementation

(Code contributed by Jiwon Seo.)

The documentation portion of the patch is being re-worked and will be
checked-in soon.  Likewise, PEP 289 will be updated to reflect Guido's
rationale for the design decisions on binding behavior (as described in
in his patch comments and in discussions on python-dev).

The test file, test_genexps.py, is written in doctest format and is
meant to exercise all aspects of the the patch.  Further additions are
welcome from everyone.  Please stress test this new feature as much as
possible before the alpha release.

1 files changed, 276 insertions, 7 deletions

diff --git a/Python/compile.c b/Python/compile.c
index 7bbcd62..15159f8 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -744,11 +744,15 @@ static int com_add(struct compiling *, PyObject *, PyObject *, PyObject *);
 static int com_addconst(struct compiling *, PyObject *);
 static int com_addname(struct compiling *, PyObject *);
 static void com_addopname(struct compiling *, int, node *);
+static void com_test(struct compiling *c, node *n);
 static void com_list(struct compiling *, node *, int);
 static void com_list_iter(struct compiling *, node *, node *, char *);
+static void com_gen_iter(struct compiling *, node *, node *);
 static int com_argdefs(struct compiling *, node *);
 static void com_assign(struct compiling *, node *, int, node *);
 static void com_assign_name(struct compiling *, node *, int);
+static int com_make_closure(struct compiling *c, PyCodeObject *co);
+
 static PyCodeObject *icompile(node *, struct compiling *);
 static PyCodeObject *jcompile(node *, const char *, struct compiling *,
 			      PyCompilerFlags *);
@@ -759,6 +763,7 @@ static node *get_rawdocstring(node *);
 static int get_ref_type(struct compiling *, char *);
 
 /* symtable operations */
+static int symtable_lookup(struct symtable *st, char *name);
 static struct symtable *symtable_build(node *, PyFutureFeatures *,
 				       const char *filename);
 static int symtable_load_symbols(struct compiling *);
@@ -777,7 +782,10 @@ static void symtable_global(struct symtable *, node *);
 static void symtable_import(struct symtable *, node *);
 static void symtable_assign(struct symtable *, node *, int);
 static void symtable_list_comprehension(struct symtable *, node *);
+static void symtable_generator_expression(struct symtable *, node *);
 static void symtable_list_for(struct symtable *, node *);
+static void symtable_gen_for(struct symtable *, node *, int);
+static void symtable_gen_iter(struct symtable *, node *);
 
 static int symtable_update_free_vars(struct symtable *);
 static int symtable_undo_free(struct symtable *, PyObject *, PyObject *);
@@ -1589,7 +1597,7 @@ com_list_for(struct compiling *c, node *n, node *e, char *t)
 	int anchor = 0;
 	int save_begin = c->c_begin;
 
-	/* list_iter: for v in expr [list_iter] */
+	/* list_for: for v in expr [list_iter] */
 	com_node(c, CHILD(n, 3)); /* expr */
 	com_addbyte(c, GET_ITER);
 	c->c_begin = c->c_nexti;
@@ -1606,6 +1614,52 @@ com_list_for(struct compiling *c, node *n, node *e, char *t)
 }  
 
 static void
+com_gen_for(struct compiling *c, node *n, node *t, int is_outmost)
+{
+	int break_anchor = 0;
+	int anchor = 0;
+	int save_begin = c->c_begin;
+
+	REQ(n, gen_for);
+	/* gen_for: for v in test [gen_iter] */
+
+	com_addfwref(c, SETUP_LOOP, &break_anchor);
+	block_push(c, SETUP_LOOP);
+
+	if (is_outmost) {
+		com_addop_varname(c, VAR_LOAD, "[outmost-iterable]");
+		com_push(c, 1);
+	}
+	else {
+		com_node(c, CHILD(n, 3));
+		com_addbyte(c, GET_ITER); 
+	}
+
+	c->c_begin = c->c_nexti;
+	com_set_lineno(c, c->c_last_line);
+	com_addfwref(c, FOR_ITER, &anchor);
+	com_push(c, 1);
+	com_assign(c, CHILD(n, 1), OP_ASSIGN, NULL);
+
+	if (NCH(n) == 5) 
+		com_gen_iter(c, CHILD(n, 4), t);
+	else {
+		com_test(c, t);
+		com_addbyte(c, YIELD_VALUE);
+		com_pop(c, 1);
+	}
+
+	com_addoparg(c, JUMP_ABSOLUTE, c->c_begin);
+	c->c_begin = save_begin;
+
+	com_backpatch(c, anchor);
+	com_pop(c, 1); /* FOR_ITER has popped this */
+	com_addbyte(c, POP_BLOCK);
+	block_pop(c, SETUP_LOOP);
+	com_backpatch(c, break_anchor);
+}
+
+static void
 com_list_if(struct compiling *c, node *n, node *e, char *t)
 {
 	int anchor = 0;
@@ -1624,6 +1678,32 @@ com_list_if(struct compiling *c, node *n, node *e, char *t)
 }
 
 static void
+com_gen_if(struct compiling *c, node *n, node *t)
+{
+	/* gen_if: 'if' test [gen_iter] */
+	int anchor = 0;
+	int a=0;
+
+	com_node(c, CHILD(n, 1));
+	com_addfwref(c, JUMP_IF_FALSE, &a);
+	com_addbyte(c, POP_TOP);
+	com_pop(c, 1);
+
+	if (NCH(n) == 3)
+		com_gen_iter(c, CHILD(n, 2), t);
+	else {
+		com_test(c, t);
+		com_addbyte(c, YIELD_VALUE);
+		com_pop(c, 1);
+	}
+	com_addfwref(c, JUMP_FORWARD, &anchor);
+	com_backpatch(c, a);
+	/* We jump here with an extra entry which we now pop */
+	com_addbyte(c, POP_TOP);
+	com_backpatch(c, anchor);
+}
+
+static void
 com_list_iter(struct compiling *c,
 	      node *p,		/* parent of list_iter node */
 	      node *e,		/* element expression node */
@@ -1655,6 +1735,28 @@ com_list_iter(struct compiling *c,
 }
 
 static void
+com_gen_iter(struct compiling *c, node *n, node *t)
+{
+	/* gen_iter: gen_for | gen_if */
+	node *ch;
+	REQ(n, gen_iter);
+
+	ch = CHILD(n, 0);
+
+	switch (TYPE(ch)) {
+	case gen_for:
+		com_gen_for(c, ch, t, 0);
+		break;
+	case gen_if:
+		com_gen_if(c, ch, t);
+		break;
+	default:
+		com_error(c, PyExc_SystemError,
+			  "invalid gen_iter node type");
+	}
+}
+
+static void
 com_list_comprehension(struct compiling *c, node *n)
 {
 	/* listmaker: test list_for */
@@ -1689,6 +1791,52 @@ com_listmaker(struct compiling *c, node *n)
 }
 
 static void
+com_generator_expression(struct compiling *c, node *n)
+{
+	/* testlist_gexp: test gen_for */
+	/* argument: test gen_for */
+	PyCodeObject *co;
+
+	REQ(CHILD(n, 0), test); 
+	REQ(CHILD(n, 1), gen_for); 
+
+	symtable_enter_scope(c->c_symtable, "<genexpr>", TYPE(n),
+		             n->n_lineno);
+	co = icompile(n, c);
+	symtable_exit_scope(c->c_symtable);
+
+	if (co == NULL)
+		c->c_errors++;
+	else {
+		int closure = com_make_closure(c, co);
+		int i = com_addconst(c, (PyObject *)co);
+
+		com_addoparg(c, LOAD_CONST, i);
+		com_push(c, 1);
+		if (closure)
+			com_addoparg(c, MAKE_CLOSURE, 0);
+		else
+			com_addoparg(c, MAKE_FUNCTION, 0);
+
+		com_test(c, CHILD(CHILD(n, 1), 3));
+		com_addbyte(c, GET_ITER);
+		com_addoparg(c, CALL_FUNCTION, 1);
+		com_pop(c, 1);
+
+		Py_DECREF(co);
+	}
+}
+
+static void
+com_testlist_gexp(struct compiling *c, node *n)
+{
+	/* testlist_gexp: test ( gen_for | (',' test)* [','] ) */
+	if (NCH(n) > 1 && TYPE(CHILD(n, 1)) == gen_for)
+		com_generator_expression(c, n);
+	else com_list(c, n, 0);
+}
+
+static void
 com_dictmaker(struct compiling *c, node *n)
 {
 	int i;
@@ -1721,7 +1869,7 @@ com_atom(struct compiling *c, node *n)
 			com_push(c, 1);
 		}
 		else
-			com_node(c, CHILD(n, 1));
+			com_testlist_gexp(c, CHILD(n, 1));
 		break;
 	case LSQB: /* '[' [listmaker] ']' */
 		if (TYPE(CHILD(n, 1)) == RSQB) {
@@ -1857,7 +2005,7 @@ static void
 com_argument(struct compiling *c, node *n, PyObject **pkeywords)
 {
 	node *m;
-	REQ(n, argument); /* [test '='] test; really [keyword '='] test */
+	REQ(n, argument); /* [test '='] test [gen_for]; really [keyword '='] test */
 	if (NCH(n) == 1) {
 		if (*pkeywords != NULL) {
 			com_error(c, PyExc_SyntaxError,
@@ -1868,6 +2016,11 @@ com_argument(struct compiling *c, node *n, PyObject **pkeywords)
 		}
 		return;
 	}
+	if (NCH(n) == 2) {
+		com_generator_expression(c, n);
+		return;
+	}
+
 	m = n;
 	do {
 		m = CHILD(m, 0);
@@ -2723,7 +2876,8 @@ static void
 com_assign_sequence(struct compiling *c, node *n, int assigning)
 {
 	int i;
-	if (TYPE(n) != testlist && TYPE(n) != listmaker)
+	if (TYPE(n) != testlist && TYPE(n) != testlist_gexp &&
+	    TYPE(n) != listmaker)
 		REQ(n, exprlist);
 	if (assigning) {
 		i = (NCH(n)+1)/2;
@@ -2765,7 +2919,13 @@ com_assign(struct compiling *c, node *n, int assigning, node *augn)
 		case exprlist:
 		case testlist:
 		case testlist1:
+		case testlist_gexp:
 			if (NCH(n) > 1) {
+				if (TYPE(CHILD(n, 1)) == gen_for) {
+					com_error(c, PyExc_SystemError,
+				  "assign to generator expression not possible");
+					return;
+				}
 				if (assigning > OP_APPLY) {
 					com_error(c, PyExc_SyntaxError,
 				  "augmented assign to tuple not possible");
@@ -4253,6 +4413,23 @@ compile_classdef(struct compiling *c, node *n)
 }
 
 static void
+compile_generator_expression(struct compiling *c, node *n)
+{
+	/* testlist_gexp: test gen_for */
+	/* argument: test gen_for */
+	REQ(CHILD(n, 0), test); 
+	REQ(CHILD(n, 1), gen_for); 
+
+	c->c_name = "<generator expression>";
+	com_gen_for(c, CHILD(n, 1), CHILD(n, 0), 1);
+
+	com_addoparg(c, LOAD_CONST, com_addconst(c, Py_None));
+	com_push(c, 1);
+	com_addbyte(c, RETURN_VALUE);
+	com_pop(c, 1);
+}
+
+static void
 compile_node(struct compiling *c, node *n)
 {
 	com_set_lineno(c, n->n_lineno);
@@ -4300,6 +4477,11 @@ compile_node(struct compiling *c, node *n)
 		compile_classdef(c, n);
 		break;
 	
+	case testlist_gexp: /* A generator expression */
+	case argument:      /* A generator expression */
+		compile_generator_expression(c, n);
+		break;
+
 	default:
 		com_error(c, PyExc_SystemError,
 			  "compile_node: unexpected node type");
@@ -4976,7 +5158,6 @@ symtable_load_symbols(struct compiling *c)
 			}
 		}
 	}
-
 	assert(PyDict_Size(c->c_freevars) == si.si_nfrees);
 
 	if (si.si_ncells > 1) { /* one cell is always in order */
@@ -5346,11 +5527,11 @@ look_for_yield(node *n)
 			return 0;
 
 		case yield_stmt:
-			return 1;
+			return GENERATOR;
 
 		default:
 			if (look_for_yield(kid))
-				return 1;
+				return GENERATOR;
 		}
 	}
 	return 0;
@@ -5494,6 +5675,18 @@ symtable_node(struct symtable *st, node *n)
 			if (TYPE(CHILD(n, i)) >= single_input)
 				symtable_node(st, CHILD(n, i));
 		break;
+	case arglist:
+		if (NCH(n) > 1)
+			for (i = 0; i < NCH(n); ++i) {
+				node *ch = CHILD(n, i);
+				if (TYPE(ch) == argument && NCH(ch) == 2 &&
+				    TYPE(CHILD(ch, 1)) == gen_for) {
+					PyErr_SetString(PyExc_SyntaxError,
+							"invalid syntax");
+					symtable_error(st, n->n_lineno);
+					return;
+				}
+			}
 	/* The remaining cases fall through to default except in
 	   special circumstances.  This requires the individual cases
 	   to be coded with great care, even though they look like
@@ -5504,6 +5697,11 @@ symtable_node(struct symtable *st, node *n)
 			n = CHILD(n, 2);
 			goto loop;
 		}
+		else if (TYPE(n) == argument && NCH(n) == 2 &&
+			TYPE(CHILD(n, 1)) == gen_for) {
+			symtable_generator_expression(st, n);
+			break;
+		}
 		/* fall through */
 	case listmaker:
 		if (NCH(n) > 1 && TYPE(CHILD(n, 1)) == list_for) {
@@ -5511,6 +5709,13 @@ symtable_node(struct symtable *st, node *n)
 			break;
 		}
 		/* fall through */
+	case testlist_gexp:
+		if (NCH(n) > 1 && TYPE(CHILD(n, 1)) == gen_for) {
+			symtable_generator_expression(st, n); 
+			break;
+		}
+		/* fall through */
+
 	case atom:
 		if (TYPE(n) == atom && TYPE(CHILD(n, 0)) == NAME) {
 			symtable_add_use(st, STR(CHILD(n, 0)));
@@ -5715,6 +5920,26 @@ symtable_list_comprehension(struct symtable *st, node *n)
 }
 
 static void
+symtable_generator_expression(struct symtable *st, node *n)
+{
+	/* testlist_gexp: test gen_for */
+	REQ(CHILD(n, 0), test);
+	REQ(CHILD(n, 1), gen_for);
+
+	symtable_enter_scope(st, "<genexpr>", TYPE(n), n->n_lineno);
+	st->st_cur->ste_generator = GENERATOR_EXPRESSION;
+
+	symtable_add_def(st, "[outmost-iterable]", DEF_PARAM);
+	
+	symtable_gen_for(st, CHILD(n, 1), 1);
+	symtable_node(st, CHILD(n, 0));
+	symtable_exit_scope(st);
+
+	/* for outmost iterable precomputation */
+	symtable_node(st, CHILD(CHILD(n, 1), 3)); 
+}
+
+static void
 symtable_list_for(struct symtable *st, node *n)
 {
 	REQ(n, list_for);
@@ -5726,6 +5951,39 @@ symtable_list_for(struct symtable *st, node *n)
 }
 
 static void
+symtable_gen_for(struct symtable *st, node *n, int is_outmost)
+{
+	REQ(n, gen_for);
+
+	/* gen_for: for v in test [gen_iter] */
+	symtable_assign(st, CHILD(n, 1), 0);
+	if (is_outmost)
+		symtable_add_use(st, "[outmost-iterable]");
+	else
+		symtable_node(st, CHILD(n, 3));
+
+	if (NCH(n) == 5)
+		symtable_gen_iter(st, CHILD(n, 4));
+}
+
+static void
+symtable_gen_iter(struct symtable *st, node *n)
+{
+	REQ(n, gen_iter);
+
+	n = CHILD(n, 0);
+	if (TYPE(n) == gen_for)
+		symtable_gen_for(st, n, 0);
+	else {
+		REQ(n, gen_if);
+		symtable_node(st, CHILD(n, 1));
+
+		if (NCH(n) == 3)
+			symtable_gen_iter(st, CHILD(n, 2));
+	}
+}
+
+static void
 symtable_import(struct symtable *st, node *n)
 {
 	int i;
@@ -5813,6 +6071,17 @@ symtable_assign(struct symtable *st, node *n, int def_flag)
 				symtable_assign(st, CHILD(n, i), def_flag);
 		}
 		return;
+	case testlist_gexp:
+		if (NCH(n) > 1 && TYPE(CHILD(n, 1)) == gen_for) {
+			/* XXX This is an error, but the next pass
+			   will catch it. */ 
+			return;
+		} else {
+			for (i = 0; i < NCH(n); i += 2)
+				symtable_assign(st, CHILD(n, i), def_flag);
+		}
+		return;
+
 	case exprlist:
 	case testlist:
 	case testlist1: