/*

* This file includes functions to transform a concrete syntax tree (CST) to

* an abstract syntax tree (AST). The main function is PyAST_FromNode().

*

*/

#include "Python.h"

#include "Python-ast.h"

#include "grammar.h"

#include "node.h"

#include "ast.h"

#include "token.h"

#include "parsetok.h"

#include "graminit.h"

#include <assert.h>

/* XXX TO DO

- re-indent this file (should be done)

- internal error checking (freeing memory, etc.)

- syntax errors

*/

/* Data structure used internally */

struct compiling {

char *c_encoding; /* source encoding */

};

static asdl_seq *seq_for_testlist(struct compiling *, const node *);

static expr_ty ast_for_expr(struct compiling *, const node *);

static stmt_ty ast_for_stmt(struct compiling *, const node *);

static asdl_seq *ast_for_suite(struct compiling *, const node *);

static asdl_seq *ast_for_exprlist(struct compiling *, const node *, int);

static expr_ty ast_for_testlist(struct compiling *, const node *);

static expr_ty ast_for_testlist_gexp(struct compiling *, const node *);

/* Note different signature for ast_for_call */

static expr_ty ast_for_call(struct compiling *, const node *, expr_ty);

static PyObject *parsenumber(const char *);

static PyObject *parsestr(const char *s, const char *encoding);

static PyObject *parsestrplus(struct compiling *, const node *n);

extern grammar _PyParser_Grammar; /* From graminit.c */

#ifndef LINENO

#define LINENO(n) ((n)->n_lineno)

#endif

#define NEW_IDENTIFIER(n) PyString_InternFromString(STR(n))

static void

asdl_stmt_seq_free(asdl_seq* seq)

{

int n, i;

if (!seq)

return;

n = asdl_seq_LEN(seq);

for (i = 0; i < n; i++)

free_stmt(asdl_seq_GET(seq, i));

asdl_seq_free(seq); /* ok */

}

static void

asdl_expr_seq_free(asdl_seq* seq)

{

int n, i;

if (!seq)

return;

n = asdl_seq_LEN(seq);

for (i = 0; i < n; i++)

free_expr(asdl_seq_GET(seq, i));

asdl_seq_free(seq); /* ok */

}

static void

asdl_alias_seq_free(asdl_seq* seq)

{

int n, i;

if (!seq)

return;

n = asdl_seq_LEN(seq);

for (i = 0; i < n; i++)

free_alias(asdl_seq_GET(seq, i));

asdl_seq_free(seq); /* ok */

}

static void

asdl_comprehension_seq_free(asdl_seq* seq)

{

int n, i;

if (!seq)

return;

n = asdl_seq_LEN(seq);

for (i = 0; i < n; i++)

free_comprehension(asdl_seq_GET(seq, i));

asdl_seq_free(seq); /* ok */

}

/* This routine provides an invalid object for the syntax error.

The outermost routine must unpack this error and create the

proper object. We do this so that we don't have to pass

the filename to everything function.

XXX Maybe we should just pass the filename...

*/

static int

ast_error(const node *n, const char *errstr)

{

PyObject *u = Py_BuildValue("zi", errstr, LINENO(n));

if (!u)

return 0;

PyErr_SetObject(PyExc_SyntaxError, u);

Py_DECREF(u);

return 0;

}

static void

ast_error_finish(const char *filename)

{

PyObject *type, *value, *tback, *errstr, *loc, *tmp;

int lineno;

assert(PyErr_Occurred());

if (!PyErr_ExceptionMatches(PyExc_SyntaxError))

return;

PyErr_Fetch(&type, &value, &tback);

errstr = PyTuple_GetItem(value, 0);

if (!errstr)

return;

Py_INCREF(errstr);

lineno = PyInt_AsLong(PyTuple_GetItem(value, 1));

if (lineno == -1)

return;

Py_DECREF(value);

loc = PyErr_ProgramText(filename, lineno);

if (!loc) {

Py_INCREF(Py_None);

loc = Py_None;

}

tmp = Py_BuildValue("(ziOO)", filename, lineno, Py_None, loc);

Py_DECREF(loc);

if (!tmp)

return;

value = Py_BuildValue("(OO)", errstr, tmp);

Py_DECREF(errstr);

Py_DECREF(tmp);

if (!value)

return;

PyErr_Restore(type, value, tback);

}

/* num_stmts() returns number of contained statements.

Use this routine to determine how big a sequence is needed for

the statements in a parse tree. Its raison d'etre is this bit of

grammar:

stmt: simple_stmt | compound_stmt

simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE

A simple_stmt can contain multiple small_stmt elements joined

by semicolons. If the arg is a simple_stmt, the number of

small_stmt elements is returned.

*/

static int

num_stmts(const node *n)

{

int i, l;

node *ch;

switch (TYPE(n)) {

case single_input:

if (TYPE(CHILD(n, 0)) == NEWLINE)

return 0;

else

return num_stmts(CHILD(n, 0));

case file_input:

l = 0;

for (i = 0; i < NCH(n); i++) {

ch = CHILD(n, i);

if (TYPE(ch) == stmt)

l += num_stmts(ch);

}

return l;

case stmt:

return num_stmts(CHILD(n, 0));

case compound_stmt:

return 1;

case simple_stmt:

return NCH(n) / 2; /* Divide by 2 to remove count of semi-colons */

case suite:

if (NCH(n) == 1)

return num_stmts(CHILD(n, 0));

else {

l = 0;

for (i = 2; i < (NCH(n) - 1); i++)

l += num_stmts(CHILD(n, i));

return l;

}

default: {

char buf[128];

sprintf(buf, "Non-statement found: %d %d\n",

TYPE(n), NCH(n));

Py_FatalError(buf);

}

}

assert(0);

return 0;

}

/* Transform the CST rooted at node * to the appropriate AST

*/

mod_ty

PyAST_FromNode(const node *n, PyCompilerFlags *flags, const char *filename)

{

int i, j, num;

asdl_seq *stmts = NULL;

stmt_ty s;

node *ch;

struct compiling c;

if (flags && flags->cf_flags & PyCF_SOURCE_IS_UTF8) {

c.c_encoding = "utf-8";

} else if (TYPE(n) == encoding_decl) {

c.c_encoding = STR(n);

n = CHILD(n, 0);

} else {

c.c_encoding = NULL;

}

switch (TYPE(n)) {

case file_input:

stmts = asdl_seq_new(num_stmts(n));

if (!stmts)

return NULL;

for (i = 0; i < NCH(n) - 1; i++) {

ch = CHILD(n, i);

if (TYPE(ch) == NEWLINE)

continue;

REQ(ch, stmt);

num = num_stmts(ch);

if (num == 1) {

s = ast_for_stmt(&c, ch);

if (!s)

goto error;

asdl_seq_APPEND(stmts, s);

}

else {

ch = CHILD(ch, 0);

REQ(ch, simple_stmt);

for (j = 0; j < num; j++) {

s = ast_for_stmt(&c, CHILD(ch, j * 2));

if (!s)

goto error;

asdl_seq_APPEND(stmts, s);

}

}

}

return Module(stmts);

case eval_input: {

expr_ty testlist_ast;

/* XXX Why not gen_for here? */

testlist_ast = ast_for_testlist(&c, CHILD(n, 0));

if (!testlist_ast)

goto error;

return Expression(testlist_ast);

}

case single_input:

if (TYPE(CHILD(n, 0)) == NEWLINE) {

stmts = asdl_seq_new(1);

if (!stmts)

goto error;

asdl_seq_SET(stmts, 0, Pass(n->n_lineno));

return Interactive(stmts);

}

else {

n = CHILD(n, 0);

num = num_stmts(n);

stmts = asdl_seq_new(num);

if (!stmts)

goto error;

if (num == 1) {

stmt_ty s = ast_for_stmt(&c, n);

if (!s)

goto error;

asdl_seq_SET(stmts, 0, s);

}

else {

/* Only a simple_stmt can contain multiple statements. */

REQ(n, simple_stmt);

for (i = 0; i < NCH(n); i += 2) {

stmt_ty s;

if (TYPE(CHILD(n, i)) == NEWLINE)

break;

s = ast_for_stmt(&c, CHILD(n, i));

if (!s)

goto error;

asdl_seq_SET(stmts, i / 2, s);

}

}

return Interactive(stmts);

}

default:

goto error;

}

error:

if (stmts)

asdl_stmt_seq_free(stmts);

ast_error_finish(filename);

return NULL;

}

/* Return the AST repr. of the operator represented as syntax (|, ^, etc.)

*/

static operator_ty

get_operator(const node *n)

{

switch (TYPE(n)) {

case VBAR:

return BitOr;

case CIRCUMFLEX:

return BitXor;

case AMPER:

return BitAnd;

case LEFTSHIFT:

return LShift;

case RIGHTSHIFT:

return RShift;

case PLUS:

return Add;

case MINUS:

return Sub;

case STAR:

return Mult;

case SLASH:

return Div;

case DOUBLESLASH:

return FloorDiv;

case PERCENT:

return Mod;

default:

return 0;

}

}

/* Set the context ctx for expr_ty e returning 0 on success, -1 on error.

Only sets context for expr kinds that "can appear in assignment context"

(according to ../Parser/Python.asdl). For other expr kinds, it sets

an appropriate syntax error and returns false.

If e is a sequential type, items in sequence will also have their context

set.

*/

static int

set_context(expr_ty e, expr_context_ty ctx, const node *n)

{

asdl_seq *s = NULL;

switch (e->kind) {

case Attribute_kind:

if (ctx == Store &&

!strcmp(PyString_AS_STRING(e->v.Attribute.attr), "None")) {

return ast_error(n, "assignment to None");

}

e->v.Attribute.ctx = ctx;

break;

case Subscript_kind:

e->v.Subscript.ctx = ctx;

break;

case Name_kind:

if (ctx == Store &&

!strcmp(PyString_AS_STRING(e->v.Name.id), "None")) {

return ast_error(n, "assignment to None");

}

e->v.Name.ctx = ctx;

break;

case List_kind:

e->v.List.ctx = ctx;

s = e->v.List.elts;

break;

case Tuple_kind:

if (asdl_seq_LEN(e->v.Tuple.elts) == 0)

return ast_error(n, "can't assign to ()");

e->v.Tuple.ctx = ctx;

s = e->v.Tuple.elts;

break;

case Call_kind:

if (ctx == Store)

return ast_error(n, "can't assign to function call");

else if (ctx == Del)

return ast_error(n, "can't delete function call");

else

return ast_error(n, "unexpected operation on function call");

break;

case BinOp_kind:

return ast_error(n, "can't assign to operator");

case GeneratorExp_kind:

return ast_error(n, "assignment to generator expression "

"not possible");

case Num_kind:

case Str_kind:

return ast_error(n, "can't assign to literal");

default: {

char buf[300];

PyOS_snprintf(buf, sizeof(buf),

"unexpected expression in assignment %d (line %d)",

e->kind, e->lineno);

return ast_error(n, buf);

}

}

/* If the LHS is a list or tuple, we need to set the assignment

context for all the tuple elements.

*/

if (s) {

int i;

for (i = 0; i < asdl_seq_LEN(s); i++) {

if (!set_context(asdl_seq_GET(s, i), ctx, n))

return 0;

}

}

return 1;

}

static operator_ty

ast_for_augassign(const node *n)

{

REQ(n, augassign);

n = CHILD(n, 0);

switch (STR(n)[0]) {

case '+':

return Add;

case '-':

return Sub;

case '/':

if (STR(n)[1] == '/')

return FloorDiv;

else

return Div;

case '%':

return Mod;

case '<':

return LShift;

case '>':

return RShift;

case '&':

return BitAnd;

case '^':

return BitXor;

case '|':

return BitOr;

case '*':

if (STR(n)[1] == '*')

return Pow;

else

return Mult;

default:

PyErr_Format(PyExc_SystemError, "invalid augassign: %s", STR(n));

return 0;

}

}

static cmpop_ty

ast_for_comp_op(const node *n)

{

/* comp_op: '<'|'>'|'=='|'>='|'<='|'<>'|'!='|'in'|'not' 'in'|'is'

|'is' 'not'

*/

REQ(n, comp_op);

if (NCH(n) == 1) {

n = CHILD(n, 0);

switch (TYPE(n)) {

case LESS:

return Lt;

case GREATER:

return Gt;

case EQEQUAL: /* == */

return Eq;

case LESSEQUAL:

return LtE;

case GREATEREQUAL:

return GtE;

case NOTEQUAL:

return NotEq;

case NAME:

if (strcmp(STR(n), "in") == 0)

return In;

if (strcmp(STR(n), "is") == 0)

return Is;

default:

PyErr_Format(PyExc_SystemError, "invalid comp_op: %s",

STR(n));

return 0;

}

}

else if (NCH(n) == 2) {

/* handle "not in" and "is not" */

switch (TYPE(CHILD(n, 0))) {

case NAME:

if (strcmp(STR(CHILD(n, 1)), "in") == 0)

return NotIn;

if (strcmp(STR(CHILD(n, 0)), "is") == 0)

return IsNot;

default:

PyErr_Format(PyExc_SystemError, "invalid comp_op: %s %s",

STR(CHILD(n, 0)), STR(CHILD(n, 1)));

return 0;

}

}

PyErr_Format(PyExc_SystemError, "invalid comp_op: has %d children",

NCH(n));

return 0;

}

static asdl_seq *

seq_for_testlist(struct compiling *c, const node *n)

{

/* testlist: test (',' test)* [','] */

asdl_seq *seq;

expr_ty expression;

int i;

assert(TYPE(n) == testlist

|| TYPE(n) == listmaker

|| TYPE(n) == testlist_gexp

|| TYPE(n) == testlist_safe

);

seq = asdl_seq_new((NCH(n) + 1) / 2);

if (!seq)

return NULL;

for (i = 0; i < NCH(n); i += 2) {

REQ(CHILD(n, i), test);

expression = ast_for_expr(c, CHILD(n, i));

if (!expression) {

asdl_expr_seq_free(seq);

return NULL;

}

assert(i / 2 < seq->size);

asdl_seq_SET(seq, i / 2, expression);

}

return seq;

}

static expr_ty

compiler_complex_args(const node *n)

{

int i, len = (NCH(n) + 1) / 2;

expr_ty result;

asdl_seq *args = asdl_seq_new(len);

if (!args)

return NULL;

REQ(n, fplist);

for (i = 0; i < len; i++) {

const node *child = CHILD(CHILD(n, 2*i), 0);

expr_ty arg;

if (TYPE(child) == NAME) {

if (!strcmp(STR(child), "None")) {

ast_error(child, "assignment to None");

return NULL;

}

arg = Name(NEW_IDENTIFIER(child), Store, LINENO(child));

}

else

arg = compiler_complex_args(CHILD(CHILD(n, 2*i), 1));

set_context(arg, Store, n);

asdl_seq_SET(args, i, arg);

}

result = Tuple(args, Store, LINENO(n));

set_context(result, Store, n);

return result;

}

/* Create AST for argument list.

XXX TO DO:

- check for invalid argument lists like normal after default

*/

static arguments_ty

ast_for_arguments(struct compiling *c, const node *n)

{

/* parameters: '(' [varargslist] ')'

varargslist: (fpdef ['=' test] ',')* ('*' NAME [',' '**' NAME]

| '**' NAME) | fpdef ['=' test] (',' fpdef ['=' test])* [',']

*/

int i, n_args = 0, n_defaults = 0, found_default = 0;

asdl_seq *args, *defaults;

identifier vararg = NULL, kwarg = NULL;

node *ch;

if (TYPE(n) == parameters) {

if (NCH(n) == 2) /* () as argument list */

return arguments(NULL, NULL, NULL, NULL);

n = CHILD(n, 1);

}

REQ(n, varargslist);

/* first count the number of normal args & defaults */

for (i = 0; i < NCH(n); i++) {

ch = CHILD(n, i);

if (TYPE(ch) == fpdef) {

n_args++;

}

if (TYPE(ch) == EQUAL)

n_defaults++;

}

args = (n_args ? asdl_seq_new(n_args) : NULL);

if (!args && n_args)

return NULL; /* Don't need to go to NULL; nothing allocated */

defaults = (n_defaults ? asdl_seq_new(n_defaults) : NULL);

if (!defaults && n_defaults)

goto error;

/* fpdef: NAME | '(' fplist ')'

fplist: fpdef (',' fpdef)* [',']

*/

i = 0;

while (i < NCH(n)) {

ch = CHILD(n, i);

switch (TYPE(ch)) {

case fpdef:

/* XXX Need to worry about checking if TYPE(CHILD(n, i+1)) is

anything other than EQUAL or a comma? */

/* XXX Should NCH(n) check be made a separate check? */

if (i + 1 < NCH(n) && TYPE(CHILD(n, i + 1)) == EQUAL) {

asdl_seq_APPEND(defaults,

ast_for_expr(c, CHILD(n, i + 2)));

i += 2;

found_default = 1;

}

else if (found_default) {

ast_error(n,

"non-default argument follows default argument");

goto error;

}

if (NCH(ch) == 3) {

asdl_seq_APPEND(args,

compiler_complex_args(CHILD(ch, 1)));

}

else if (TYPE(CHILD(ch, 0)) == NAME) {

expr_ty name;

if (!strcmp(STR(CHILD(ch, 0)), "None")) {

ast_error(CHILD(ch, 0), "assignment to None");

goto error;

}

name = Name(NEW_IDENTIFIER(CHILD(ch, 0)),

Param, LINENO(ch));

if (!name)

goto error;

asdl_seq_APPEND(args, name);

}

i += 2; /* the name and the comma */

break;

case STAR:

if (!strcmp(STR(CHILD(n, i+1)), "None")) {

ast_error(CHILD(n, i+1), "assignment to None");

goto error;

}

vararg = NEW_IDENTIFIER(CHILD(n, i+1));

i += 3;

break;

case DOUBLESTAR:

if (!strcmp(STR(CHILD(n, i+1)), "None")) {

ast_error(CHILD(n, i+1), "assignment to None");

goto error;

}

kwarg = NEW_IDENTIFIER(CHILD(n, i+1));

i += 3;

break;

default:

PyErr_Format(PyExc_SystemError,

"unexpected node in varargslist: %d @ %d",

TYPE(ch), i);

goto error;

}

}

return arguments(args, vararg, kwarg, defaults);

error:

Py_XDECREF(vararg);

Py_XDECREF(kwarg);

if (args)

asdl_expr_seq_free(args);

if (defaults)

asdl_expr_seq_free(defaults);

return NULL;

}

static expr_ty

ast_for_dotted_name(struct compiling *c, const node *n)

{

expr_ty e = NULL;

expr_ty attrib = NULL;

identifier id = NULL;

int i;

REQ(n, dotted_name);

id = NEW_IDENTIFIER(CHILD(n, 0));

if (!id)

goto error;

e = Name(id, Load, LINENO(n));

if (!e)

goto error;

id = NULL;

for (i = 2; i < NCH(n); i+=2) {

id = NEW_IDENTIFIER(CHILD(n, i));

if (!id)

goto error;

attrib = Attribute(e, id, Load, LINENO(CHILD(n, i)));

if (!attrib)

goto error;

e = attrib;

attrib = NULL;

}

return e;

error:

Py_XDECREF(id);

free_expr(e);

return NULL;

}

static expr_ty

ast_for_decorator(struct compiling *c, const node *n)

{

/* decorator: '@' dotted_name [ '(' [arglist] ')' ] NEWLINE */

expr_ty d = NULL;

expr_ty name_expr = NULL;

REQ(n, decorator);

if ((NCH(n) < 3 && NCH(n) != 5 && NCH(n) != 6)

|| TYPE(CHILD(n, 0)) != AT || TYPE(RCHILD(n, -1)) != NEWLINE) {

ast_error(n, "Invalid decorator node");

goto error;

}

name_expr = ast_for_dotted_name(c, CHILD(n, 1));

if (!name_expr)

goto error;

if (NCH(n) == 3) { /* No arguments */

d = name_expr;

name_expr = NULL;

}

else if (NCH(n) == 5) { /* Call with no arguments */

d = Call(name_expr, NULL, NULL, NULL, NULL, LINENO(n));

if (!d)

goto error;

name_expr = NULL;

}

else {

d = ast_for_call(c, CHILD(n, 3), name_expr);

if (!d)

goto error;

name_expr = NULL;

}

return d;

error:

free_expr(name_expr);

free_expr(d);

return NULL;

}

static asdl_seq*

ast_for_decorators(struct compiling *c, const node *n)

{

asdl_seq* decorator_seq = NULL;

expr_ty d;

int i;

REQ(n, decorators);

decorator_seq = asdl_seq_new(NCH(n));

if (!decorator_seq)

return NULL;

for (i = 0; i < NCH(n); i++) {

d = ast_for_decorator(c, CHILD(n, i));

if (!d)

goto error;

asdl_seq_APPEND(decorator_seq, d);

}

return decorator_seq;

error:

asdl_expr_seq_free(decorator_seq);

return NULL;

}

static stmt_ty

ast_for_funcdef(struct compiling *c, const node *n)

{

/* funcdef: 'def' [decorators] NAME parameters ':' suite */

identifier name = NULL;

arguments_ty args = NULL;

asdl_seq *body = NULL;

asdl_seq *decorator_seq = NULL;

int name_i;

REQ(n, funcdef);

if (NCH(n) == 6) { /* decorators are present */

decorator_seq = ast_for_decorators(c, CHILD(n, 0));

if (!decorator_seq)

goto error;

name_i = 2;

}

else {

name_i = 1;

}

name = NEW_IDENTIFIER(CHILD(n, name_i));

if (!name)

goto error;

else if (!strcmp(STR(CHILD(n, name_i)), "None")) {

ast_error(CHILD(n, name_i), "assignment to None");

goto error;

}

args = ast_for_arguments(c, CHILD(n, name_i + 1));

if (!args)

goto error;

body = ast_for_suite(c, CHILD(n, name_i + 3));

if (!body)

goto error;

return FunctionDef(name, args, body, decorator_seq, LINENO(n));

error:

asdl_stmt_seq_free(body);

asdl_expr_seq_free(decorator_seq);

free_arguments(args);

Py_XDECREF(name);

return NULL;

}

static expr_ty

ast_for_lambdef(struct compiling *c, const node *n)

{

/* lambdef: 'lambda' [varargslist] ':' test */

arguments_ty args;

expr_ty expression;

if (NCH(n) == 3) {

args = arguments(NULL, NULL, NULL, NULL);

if (!args)

return NULL;

expression = ast_for_expr(c, CHILD(n, 2));

if (!expression) {

free_arguments(args);

return NULL;

}

}

else {

args = ast_for_arguments(c, CHILD(n, 1));

if (!args)

return NULL;

expression = ast_for_expr(c, CHILD(n, 3));

if (!expression) {

free_arguments(args);

return NULL;

}

}

return Lambda(args, expression, LINENO(n));

}

/* Count the number of 'for' loop in a list comprehension.

Helper for ast_for_listcomp().

*/

static int

count_list_fors(const node *n)

{

int n_fors = 0;

node *ch = CHILD(n, 1);

count_list_for:

n_fors++;

REQ(ch, list_for);

if (NCH(ch) == 5)

ch = CHILD(ch, 4);

else

return n_fors;

count_list_iter:

REQ(ch, list_iter);

ch = CHILD(ch, 0);

if (TYPE(ch) == list_for)

goto count_list_for;

else if (TYPE(ch) == list_if) {

if (NCH(ch) == 3) {

ch = CHILD(ch, 2);

goto count_list_iter;

}

else

return n_fors;

}

else {

/* Should never be reached */

PyErr_SetString(PyExc_SystemError, "logic error in count_list_fors");

return -1;

}

}

/* Count the number of 'if' statements in a list comprehension.

Helper for ast_for_listcomp().

*/

static int

count_list_ifs(const node *n)

{

int n_ifs = 0;

count_list_iter:

REQ(n, list_iter);

if (TYPE(CHILD(n, 0)) == list_for)

return n_ifs;

n = CHILD(n, 0);

REQ(n, list_if);

n_ifs++;

if (NCH(n) == 2)

return n_ifs;

n = CHILD(n, 2);

goto count_list_iter;

}

static expr_ty

ast_for_listcomp(struct compiling *c, const node *n)

{

/* listmaker: test ( list_for | (',' test)* [','] )

list_for: 'for' exprlist 'in' testlist_safe [list_iter]

list_iter: list_for | list_if

list_if: 'if' test [list_iter]

testlist_safe: test [(',' test)+ [',']]

*/

expr_ty elt;

asdl_seq *listcomps;

int i, n_fors;

node *ch;

REQ(n, listmaker);

assert(NCH(n) > 1);

elt = ast_for_expr(c, CHILD(n, 0));

if (!elt)

return NULL;

n_fors = count_list_fors(n);

if (n_fors == -1)

return NULL;

listcomps = asdl_seq_new(n_fors);

if (!listcomps) {

free_expr(elt);

return NULL;

}

ch = CHILD(n, 1);

for (i = 0; i < n_fors; i++) {

comprehension_ty lc;

asdl_seq *t;

expr_ty expression;

REQ(ch, list_for);