source: vendor/python/2.5/Python/future.c

#include "Python.h"
#include "Python-ast.h"
#include "node.h"
#include "token.h"
#include "graminit.h"
#include "code.h"
#include "compile.h"
#include "symtable.h"

#define UNDEFINED_FUTURE_FEATURE "future feature %.100s is not defined"

static int
future_check_features(PyFutureFeatures *ff, stmt_ty s, const char *filename)
{
        int i;
        asdl_seq *names;

        assert(s->kind == ImportFrom_kind);

        names = s->v.ImportFrom.names;
        for (i = 0; i < asdl_seq_LEN(names); i++) {
                alias_ty name = (alias_ty)asdl_seq_GET(names, i);
                const char *feature = PyString_AsString(name->name);
                if (!feature)
                        return 0;
                if (strcmp(feature, FUTURE_NESTED_SCOPES) == 0) {
                        continue;
                } else if (strcmp(feature, FUTURE_GENERATORS) == 0) {
                        continue;
                } else if (strcmp(feature, FUTURE_DIVISION) == 0) {
                        ff->ff_features |= CO_FUTURE_DIVISION;
                } else if (strcmp(feature, FUTURE_ABSOLUTE_IMPORT) == 0) {
                        ff->ff_features |= CO_FUTURE_ABSOLUTE_IMPORT;
                } else if (strcmp(feature, FUTURE_WITH_STATEMENT) == 0) {
                        ff->ff_features |= CO_FUTURE_WITH_STATEMENT;
                } else if (strcmp(feature, "braces") == 0) {
                        PyErr_SetString(PyExc_SyntaxError,
                                        "not a chance");
                        PyErr_SyntaxLocation(filename, s->lineno);
                        return 0;
                } else {
                        PyErr_Format(PyExc_SyntaxError,
                                     UNDEFINED_FUTURE_FEATURE, feature);
                        PyErr_SyntaxLocation(filename, s->lineno);
                        return 0;
                }
        }
        return 1;
}

static int
future_parse(PyFutureFeatures *ff, mod_ty mod, const char *filename)
{
        int i, found_docstring = 0, done = 0, prev_line = 0;

        static PyObject *future;
        if (!future) {
                future = PyString_InternFromString("__future__");
                if (!future)
                        return 0;
        }

        if (!(mod->kind == Module_kind || mod->kind == Interactive_kind))
                return 1;

        /* A subsequent pass will detect future imports that don't
           appear at the beginning of the file.  There's one case,
           however, that is easier to handl here: A series of imports
           joined by semi-colons, where the first import is a future
           statement but some subsequent import has the future form
           but is preceded by a regular import.
        */
           

        for (i = 0; i < asdl_seq_LEN(mod->v.Module.body); i++) {
                stmt_ty s = (stmt_ty)asdl_seq_GET(mod->v.Module.body, i);

                if (done && s->lineno > prev_line)
                        return 1;
                prev_line = s->lineno;

                /* The tests below will return from this function unless it is
                   still possible to find a future statement.  The only things
                   that can precede a future statement are another future
                   statement and a doc string.
                */

                if (s->kind == ImportFrom_kind) {
                        if (s->v.ImportFrom.module == future) {
                                if (done) {
                                        PyErr_SetString(PyExc_SyntaxError,
                                                        ERR_LATE_FUTURE);
                                        PyErr_SyntaxLocation(filename, 
                                                             s->lineno);
                                        return 0;
                                }
                                if (!future_check_features(ff, s, filename))
                                        return 0;
                                ff->ff_lineno = s->lineno;
                        }
                        else
                                done = 1;
                }
                else if (s->kind == Expr_kind && !found_docstring) {
                        expr_ty e = s->v.Expr.value;
                        if (e->kind != Str_kind)
                                done = 1;
                        else
                                found_docstring = 1;
                }
                else
                        done = 1;
        }
        return 1;
}


PyFutureFeatures *
PyFuture_FromAST(mod_ty mod, const char *filename)
{
        PyFutureFeatures *ff;

        ff = (PyFutureFeatures *)PyObject_Malloc(sizeof(PyFutureFeatures));
        if (ff == NULL) {
                PyErr_NoMemory();
                return NULL;
        }
        ff->ff_features = 0;
        ff->ff_lineno = -1;

        if (!future_parse(ff, mod, filename)) {
                PyObject_Free(ff);
                return NULL;
        }
        return ff;
}