Patch #1810 by Thomas Lee, reviewed by myself:

allow compiling Python AST objects into code objects
in compile().

Doc/library/_ast.rst

@@ -12,16 +12,16 @@ Abstract Syntax Trees
 .. versionadded:: 2.5
 
 The ``_ast`` module helps Python applications to process trees of the Python
-abstract syntax grammar. The Python compiler currently provides read-only access
-to such trees, meaning that applications can only create a tree for a given
-piece of Python source code; generating :term:`bytecode` from a (potentially modified)
-tree is not supported. The abstract syntax itself might change with each Python
-release; this module helps to find out programmatically what the current grammar
-looks like.
+abstract syntax grammar.  The abstract syntax itself might change with each
+Python release; this module helps to find out programmatically what the current
+grammar looks like.
 
-An abstract syntax tree can be generated by passing ``_ast.PyCF_ONLY_AST`` as a
-flag to the :func:`compile` builtin function. The result will be a tree of
-objects whose classes all inherit from ``_ast.AST``.
+An abstract syntax tree can be generated by passing :data:`_ast.PyCF_ONLY_AST`
+as a flag to the :func:`compile` builtin function. The result will be a tree of
+objects whose classes all inherit from :class:`_ast.AST`.
+
+A modified abstract syntax tree can be compiled into a Python code object using
+the built-in :func:`compile` function.
 
 The actual classes are derived from the ``Parser/Python.asdl`` file, which is
 reproduced below. There is one class defined for each left-hand side symbol in
@@ -47,6 +47,9 @@ If these attributes are marked as optional in the grammar (using a question
 mark), the value might be ``None``. If the attributes can have zero-or-more
 values (marked with an asterisk), the values are represented as Python lists.
 
+The constructors of all ``_ast`` classes don't take arguments; instead, if you
+create instances, you must assign the required attributes separately.
+
 
 Abstract Grammar
 ----------------

Doc/library/compiler.rst

@@ -28,12 +28,6 @@ code.
 This chapter explains how the various components of the :mod:`compiler` package
 work.  It blends reference material with a tutorial.
 
-The following modules are part of the :mod:`compiler` package:
-
-.. toctree::
-
-   _ast.rst
-
 
 The basic interface
 ===================

Doc/library/functions.rst

@@ -190,21 +190,27 @@ available.  They are listed here in alphabetical order.
 
 .. function:: compile(source, filename, mode[, flags[, dont_inherit]])
 
-   Compile the *source* into a code object.  Code objects can be executed by an
-   :keyword:`exec` statement or evaluated by a call to :func:`eval`.  The
-   *filename* argument should give the file from which the code was read; pass some
-   recognizable value if it wasn't read from a file (``'<string>'`` is commonly
-   used). The *mode* argument specifies what kind of code must be compiled; it can
-   be ``'exec'`` if *source* consists of a sequence of statements, ``'eval'`` if it
-   consists of a single expression, or ``'single'`` if it consists of a single
-   interactive statement (in the latter case, expression statements that evaluate
-   to something else than ``None`` will be printed).
+   Compile the *source* into a code or AST object.  Code objects can be executed
+   by an :keyword:`exec` statement or evaluated by a call to :func:`eval`.
+   *source* can either be a string or an AST object.  Refer to the :mod:`_ast`
+   module documentation for information on how to compile into and from AST
+   objects.
 
-   When compiling multi-line statements, two caveats apply: line endings must be
-   represented by a single newline character (``'\n'``), and the input must be
-   terminated by at least one newline character.  If line endings are represented
-   by ``'\r\n'``, use the string :meth:`replace` method to change them into
-   ``'\n'``.
+   When compiling a string with multi-line statements, two caveats apply: line
+   endings must be represented by a single newline character (``'\n'``), and the
+   input must be terminated by at least one newline character.  If line endings
+   are represented by ``'\r\n'``, use the string :meth:`replace` method to
+   change them into ``'\n'``.
+
+   The *filename* argument should give the file from which the code was read;
+   pass some recognizable value if it wasn't read from a file (``'<string>'`` is
+   commonly used).
+
+   The *mode* argument specifies what kind of code must be compiled; it can be
+   ``'exec'`` if *source* consists of a sequence of statements, ``'eval'`` if it
+   consists of a single expression, or ``'single'`` if it consists of a single
+   interactive statement (in the latter case, expression statements that
+   evaluate to something else than ``None`` will be printed).
 
    The optional arguments *flags* and *dont_inherit* (which are new in Python 2.2)
    control which future statements (see :pep:`236`) affect the compilation of
@@ -224,6 +230,9 @@ available.  They are listed here in alphabetical order.
    This function raises :exc:`SyntaxError` if the compiled source is invalid,
    and :exc:`TypeError` if the source contains null bytes.
 
+   .. versionadded:: 2.6
+      Support for compiling AST objects.
+
 
 .. function:: complex([real[, imag]])
 

Doc/library/language.rst

@@ -15,6 +15,7 @@ These modules include:
 .. toctree::
 
    parser.rst
+   _ast.rst
    symbol.rst
    token.rst
    keyword.rst

Include/Python-ast.h

@@ -501,3 +501,5 @@ keyword_ty _Py_keyword(identifier arg, expr_ty value, PyArena *arena);
 alias_ty _Py_alias(identifier name, identifier asname, PyArena *arena);
 
 PyObject* PyAST_mod2obj(mod_ty t);
+mod_ty PyAST_obj2mod(PyObject* ast, PyArena* arena);
+int PyAST_Check(PyObject* obj);

Lib/test/test_compile.py

 import unittest
 import sys
+import _ast
 from test import test_support
 
 class TestSpecifics(unittest.TestCase):
@@ -416,6 +417,32 @@ if 1:
         self.assert_("_A__mangled_mod" in A.f.func_code.co_varnames)
         self.assert_("__package__" in A.f.func_code.co_varnames)
 
+    def test_compile_ast(self):
+        fname = __file__
+        if fname.lower().endswith(('pyc', 'pyo')):
+            fname = fname[:-1]
+        with open(fname, 'r') as f:
+            fcontents = f.read()
+        sample_code = [
+            ['<assign>', 'x = 5'],
+            ['<print1>', 'print 1'],
+            ['<printv>', 'print v'],
+            ['<printTrue>', 'print True'],
+            ['<printList>', 'print []'],
+            ['<ifblock>', """if True:\n    pass\n"""],
+            ['<forblock>', """for n in [1, 2, 3]:\n    print n\n"""],
+            ['<deffunc>', """def foo():\n    pass\nfoo()\n"""],
+            [fname, fcontents],
+        ]
+
+        for fname, code in sample_code:
+            co1 = compile(code, '%s1' % fname, 'exec')
+            ast = compile(code, '%s2' % fname, 'exec', _ast.PyCF_ONLY_AST)
+            self.assert_(type(ast) == _ast.Module)
+            co2 = compile(ast, '%s3' % fname, 'exec')
+            self.assertEqual(co1, co2)
+
+
 def test_main():
     test_support.run_unittest(TestSpecifics)
 

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.6 alpha 2?
 Core and builtins
 -----------------
 
+- Patch #1810: compile() can now compile _ast trees as returned by
+  compile(..., PyCF_ONLY_AST).
+
 - Patch #2426: Added sqlite3.Connection.iterdump method to allow easy dumping
   of databases.  Contributed by Paul Kippes at PyCon 2008.
 

Parser/asdl_c.py

@@ -73,12 +73,12 @@ def is_simple(sum):
     A sum is simple if its types have no fields, e.g.
     unaryop = Invert | Not | UAdd | USub
     """
-
     for t in sum.types:
         if t.fields:
             return False
     return True
 
+
 class EmitVisitor(asdl.VisitorBase):
     """Visit that emits lines"""
 
@@ -96,6 +96,7 @@ class EmitVisitor(asdl.VisitorBase):
             line = (" " * TABSIZE * depth) + line + "\n"
             self.file.write(line)
 
+
 class TypeDefVisitor(EmitVisitor):
     def visitModule(self, mod):
         for dfn in mod.dfns:
@@ -133,6 +134,7 @@ class TypeDefVisitor(EmitVisitor):
         self.emit(s, depth)
         self.emit("", depth)
 
+
 class StructVisitor(EmitVisitor):
     """Visitor to generate typdefs for AST."""
 
@@ -202,6 +204,7 @@ class StructVisitor(EmitVisitor):
         self.emit("};", depth)
         self.emit("", depth)
 
+
 class PrototypeVisitor(EmitVisitor):
     """Generate function prototypes for the .h file"""
 
@@ -271,6 +274,7 @@ class PrototypeVisitor(EmitVisitor):
         self.emit_function(name, get_c_type(name),
                            self.get_args(prod.fields), [], union=0)
 
+
 class FunctionVisitor(PrototypeVisitor):
     """Visitor to generate constructor functions for AST."""
 
@@ -325,6 +329,7 @@ class FunctionVisitor(PrototypeVisitor):
             emit("p->%s = %s;" % (argname, argname), 1)
         assert not attrs
 
+
 class PickleVisitor(EmitVisitor):
 
     def visitModule(self, mod):
@@ -346,6 +351,181 @@ class PickleVisitor(EmitVisitor):
     def visitField(self, sum):
         pass
 
+
+class Obj2ModPrototypeVisitor(PickleVisitor):
+    def visitProduct(self, prod, name):
+        code = "static int obj2ast_%s(PyObject* obj, %s* out, PyArena* arena);"
+        self.emit(code % (name, get_c_type(name)), 0)
+
+    visitSum = visitProduct
+
+
+class Obj2ModVisitor(PickleVisitor):
+    def funcHeader(self, name):
+        ctype = get_c_type(name)
+        self.emit("int", 0)
+        self.emit("obj2ast_%s(PyObject* obj, %s* out, PyArena* arena)" % (name, ctype), 0)
+        self.emit("{", 0)
+        self.emit("PyObject* tmp = NULL;", 1)
+        self.emit("", 0)
+
+    def sumTrailer(self, name):
+        self.emit("", 0)
+        self.emit("tmp = PyObject_Repr(obj);", 1)
+        # there's really nothing more we can do if this fails ...
+        self.emit("if (tmp == NULL) goto failed;", 1)
+        error = "expected some sort of %s, but got %%.400s" % name
+        format = "PyErr_Format(PyExc_TypeError, \"%s\", PyString_AS_STRING(tmp));"
+        self.emit(format % error, 1, reflow=False)
+        self.emit("failed:", 0)
+        self.emit("Py_XDECREF(tmp);", 1)
+        self.emit("return 1;", 1)
+        self.emit("}", 0)
+        self.emit("", 0)
+
+    def simpleSum(self, sum, name):
+        self.funcHeader(name)
+        for t in sum.types:
+            self.emit("if (PyObject_IsInstance(obj, (PyObject*)%s_type)) {" % t.name, 1)
+            self.emit("*out = %s;" % t.name, 2)
+            self.emit("return 0;", 2)
+            self.emit("}", 1)
+        self.sumTrailer(name)
+
+    def buildArgs(self, fields):
+        return ", ".join(fields + ["arena"])
+
+    def complexSum(self, sum, name):
+        self.funcHeader(name)
+        for a in sum.attributes:
+            self.visitAttributeDeclaration(a, name, sum=sum)
+        self.emit("", 0)
+        # XXX: should we only do this for 'expr'?
+        self.emit("if (obj == Py_None) {", 1)
+        self.emit("*out = NULL;", 2)
+        self.emit("return 0;", 2)
+        self.emit("}", 1)
+        for a in sum.attributes:
+            self.visitField(a, name, sum=sum, depth=1)
+        for t in sum.types:
+            self.emit("if (PyObject_IsInstance(obj, (PyObject*)%s_type)) {" % t.name, 1)
+            for f in t.fields:
+                self.visitFieldDeclaration(f, t.name, sum=sum, depth=2)
+            self.emit("", 0)
+            for f in t.fields:
+                self.visitField(f, t.name, sum=sum, depth=2)
+            args = [f.name.value for f in t.fields] + [a.name.value for a in sum.attributes]
+            self.emit("*out = %s(%s);" % (t.name, self.buildArgs(args)), 2)
+            self.emit("if (*out == NULL) goto failed;", 2)
+            self.emit("return 0;", 2)
+            self.emit("}", 1)
+        self.sumTrailer(name)
+
+    def visitAttributeDeclaration(self, a, name, sum=sum):
+        ctype = get_c_type(a.type)
+        self.emit("%s %s;" % (ctype, a.name), 1)
+
+    def visitSum(self, sum, name):
+        if is_simple(sum):
+            self.simpleSum(sum, name)
+        else:
+            self.complexSum(sum, name)
+
+    def visitProduct(self, prod, name):
+        ctype = get_c_type(name)
+        self.emit("int", 0)
+        self.emit("obj2ast_%s(PyObject* obj, %s* out, PyArena* arena)" % (name, ctype), 0)
+        self.emit("{", 0)
+        self.emit("PyObject* tmp = NULL;", 1)
+        for f in prod.fields:
+            self.visitFieldDeclaration(f, name, prod=prod, depth=1)
+        self.emit("", 0)
+        for f in prod.fields:
+            self.visitField(f, name, prod=prod, depth=1)
+        args = [f.name.value for f in prod.fields]
+        self.emit("*out = %s(%s);" % (name, self.buildArgs(args)), 1)
+        self.emit("return 0;", 1)
+        self.emit("failed:", 0)
+        self.emit("Py_XDECREF(tmp);", 1)
+        self.emit("return 1;", 1)
+        self.emit("}", 0)
+        self.emit("", 0)
+
+    def visitFieldDeclaration(self, field, name, sum=None, prod=None, depth=0):
+        ctype = get_c_type(field.type)
+        if field.seq:
+            if self.isSimpleType(field):
+                self.emit("asdl_int_seq* %s;" % field.name, depth)
+            else:
+                self.emit("asdl_seq* %s;" % field.name, depth)
+        else:
+            ctype = get_c_type(field.type)
+            self.emit("%s %s;" % (ctype, field.name), depth)
+
+    def isSimpleSum(self, field):
+        # XXX can the members of this list be determined automatically?
+        return field.type.value in ('expr_context', 'boolop', 'operator',
+                                    'unaryop', 'cmpop')
+
+    def isNumeric(self, field):
+        return get_c_type(field.type) in ("int", "bool")
+
+    def isSimpleType(self, field):
+        return self.isSimpleSum(field) or self.isNumeric(field)
+
+    def visitField(self, field, name, sum=None, prod=None, depth=0):
+        ctype = get_c_type(field.type)
+        self.emit("if (PyObject_HasAttrString(obj, \"%s\")) {" % field.name, depth)
+        self.emit("int res;", depth+1)
+        if field.seq:
+            self.emit("Py_ssize_t len;", depth+1)
+            self.emit("Py_ssize_t i;", depth+1)
+        self.emit("tmp = PyObject_GetAttrString(obj, \"%s\");" % field.name, depth+1)
+        self.emit("if (tmp == NULL) goto failed;", depth+1)
+        if field.seq:
+            self.emit("if (!PyList_Check(tmp)) {", depth+1)
+            self.emit("PyErr_Format(PyExc_TypeError, \"%s field \\\"%s\\\" must "
+                      "be a list, not a %%.200s\", tmp->ob_type->tp_name);" %
+                      (name, field.name),
+                      depth+2, reflow=False)
+            self.emit("goto failed;", depth+2)
+            self.emit("}", depth+1)
+            self.emit("len = PyList_GET_SIZE(tmp);", depth+1)
+            if self.isSimpleType(field):
+                self.emit("%s = asdl_int_seq_new(len, arena);" % field.name, depth+1)
+            else:
+                self.emit("%s = asdl_seq_new(len, arena);" % field.name, depth+1)
+            self.emit("if (%s == NULL) goto failed;" % field.name, depth+1)
+            self.emit("for (i = 0; i < len; i++) {", depth+1)
+            self.emit("%s value;" % ctype, depth+2)
+            self.emit("res = obj2ast_%s(PyList_GET_ITEM(tmp, i), &value, arena);" %
+                      field.type, depth+2, reflow=False)
+            self.emit("if (res != 0) goto failed;", depth+2)
+            self.emit("asdl_seq_SET(%s, i, value);" % field.name, depth+2)
+            self.emit("}", depth+1)
+        else:
+            self.emit("res = obj2ast_%s(tmp, &%s, arena);" %
+                      (field.type, field.name), depth+1)
+            self.emit("if (res != 0) goto failed;", depth+1)
+
+        self.emit("Py_XDECREF(tmp);", depth+1)
+        self.emit("tmp = NULL;", depth+1)
+        self.emit("} else {", depth)
+        if not field.opt:
+            message = "required field \\\"%s\\\" missing from %s" % (field.name, name)
+            format = "PyErr_SetString(PyExc_TypeError, \"%s\");"
+            self.emit(format % message, depth+1, reflow=False)
+            self.emit("return 1;", depth+1)
+        else:
+            if self.isNumeric(field):
+                self.emit("%s = 0;" % field.name, depth+1)
+            elif not self.isSimpleType(field):
+                self.emit("%s = NULL;" % field.name, depth+1)
+            else:
+                raise TypeError("could not determine the default value for %s" % field.name)
+        self.emit("}", depth)
+
+
 class MarshalPrototypeVisitor(PickleVisitor):
 
     def prototype(self, sum, name):
@@ -355,6 +535,7 @@ class MarshalPrototypeVisitor(PickleVisitor):
 
     visitProduct = visitSum = prototype
 
+
 class PyTypesDeclareVisitor(PickleVisitor):
 
     def visitProduct(self, prod, name):
@@ -440,6 +621,8 @@ static int add_attributes(PyTypeObject* type, char**attrs, int num_fields)
     return result;
 }
 
+/* Conversion AST -> Python */
+
 static PyObject* ast2obj_list(asdl_seq *seq, PyObject* (*func)(void*))
 {
     int i, n = asdl_seq_LEN(seq);
@@ -476,6 +659,57 @@ static PyObject* ast2obj_int(long b)
 {
     return PyInt_FromLong(b);
 }
+
+/* Conversion Python -> AST */
+
+static int obj2ast_object(PyObject* obj, PyObject** out, PyArena* arena)
+{
+    if (obj == Py_None)
+        obj = NULL;
+    if (obj)
+        PyArena_AddPyObject(arena, obj);
+    Py_XINCREF(obj);
+    *out = obj;
+    return 0;
+}
+
+#define obj2ast_identifier obj2ast_object
+#define obj2ast_string obj2ast_object
+
+static int obj2ast_int(PyObject* obj, int* out, PyArena* arena)
+{
+    int i;
+    if (!PyInt_Check(obj) && !PyLong_Check(obj)) {
+        PyObject *s = PyObject_Repr(obj);
+        if (s == NULL) return 1;
+        PyErr_Format(PyExc_ValueError, "invalid integer value: %.400s",
+                     PyString_AS_STRING(s));
+        Py_DECREF(s);
+        return 1;
+    }
+
+    i = (int)PyLong_AsLong(obj);
+    if (i == -1 && PyErr_Occurred())
+        return 1;
+    *out = i;
+    return 0;
+}
+
+static int obj2ast_bool(PyObject* obj, bool* out, PyArena* arena)
+{
+    if (!PyBool_Check(obj)) {
+        PyObject *s = PyObject_Repr(obj);
+        if (s == NULL) return 1;
+        PyErr_Format(PyExc_ValueError, "invalid boolean value: %.400s",
+                     PyString_AS_STRING(s));
+        Py_DECREF(s);
+        return 1;
+    }
+
+    *out = (obj == Py_True);
+    return 0;
+}
+
 """, 0, reflow=False)
 
         self.emit("static int init_types(void)",0)
@@ -523,6 +757,7 @@ static PyObject* ast2obj_int(long b)
                              (cons.name, cons.name), 1)
             self.emit("if (!%s_singleton) return 0;" % cons.name, 1)
 
+
 def parse_version(mod):
     return mod.version.value[12:-3]
 
@@ -562,6 +797,7 @@ class ASTModuleVisitor(PickleVisitor):
     def addObj(self, name):
         self.emit('if (PyDict_SetItemString(d, "%s", (PyObject*)%s_type) < 0) return;' % (name, name), 1)
 
+
 _SPECIALIZED_SEQUENCES = ('stmt', 'expr')
 
 def find_sequence(fields, doing_specialization):
@@ -587,6 +823,7 @@ class StaticVisitor(PickleVisitor):
     def visit(self, object):
         self.emit(self.CODE, 0, reflow=False)
 
+
 class ObjVisitor(PickleVisitor):
 
     def func_begin(self, name):
@@ -637,8 +874,12 @@ class ObjVisitor(PickleVisitor):
             self.emit("case %s:" % t.name, 2)
             self.emit("Py_INCREF(%s_singleton);" % t.name, 3)
             self.emit("return %s_singleton;" % t.name, 3)
+        self.emit("default:" % name, 2)
+        self.emit('/* should never happen, but just in case ... */', 3)
+        code = "PyErr_Format(PyExc_SystemError, \"unknown %s found\");" % name
+        self.emit(code, 3, reflow=False)
+        self.emit("return NULL;", 3)
         self.emit("}", 1)
-        self.emit("return NULL; /* cannot happen */", 1)
         self.emit("}", 0)
 
     def visitProduct(self, prod, name):
@@ -712,6 +953,27 @@ PyObject* PyAST_mod2obj(mod_ty t)
     init_types();
     return ast2obj_mod(t);
 }
+
+mod_ty PyAST_obj2mod(PyObject* ast, PyArena* arena)
+{
+    mod_ty res;
+    init_types();
+    if (!PyObject_IsInstance(ast, mod_type)) {
+        PyErr_SetString(PyExc_TypeError, "expected either Module, Interactive "
+                        "or Expression node");
+        return NULL;
+    }
+    if (obj2ast_mod(ast, &res, arena) != 0)
+        return NULL;
+    else
+        return res;
+}
+
+int PyAST_Check(PyObject* obj)
+{
+    init_types();
+    return PyObject_IsInstance(obj, (PyObject*)AST_type);
+}
 """
 
 class ChainOfVisitors:
@@ -754,6 +1016,8 @@ def main(srcfile):
                             )
         c.visit(mod)
         print >>f, "PyObject* PyAST_mod2obj(mod_ty t);"
+        print >>f, "mod_ty PyAST_obj2mod(PyObject* ast, PyArena* arena);"
+        print >>f, "int PyAST_Check(PyObject* obj);"
         f.close()
 
     if SRC_DIR:
@@ -768,8 +1032,10 @@ def main(srcfile):
         v = ChainOfVisitors(
             PyTypesDeclareVisitor(f),
             PyTypesVisitor(f),
+            Obj2ModPrototypeVisitor(f),
             FunctionVisitor(f),
             ObjVisitor(f),
+            Obj2ModVisitor(f),
             ASTModuleVisitor(f),
             PartingShots(f),
             )

Python/bltinmodule.c

 /* Built-in functions */
 
 #include "Python.h"
+#include "Python-ast.h"
 
 #include "node.h"
 #include "code.h"
@@ -481,6 +482,41 @@ builtin_compile(PyObject *self, PyObject *args, PyObject *kwds)
 
 	cf.cf_flags = supplied_flags;
 
+	if (supplied_flags &
+	    ~(PyCF_MASK | PyCF_MASK_OBSOLETE | PyCF_DONT_IMPLY_DEDENT | PyCF_ONLY_AST))
+	{
+		PyErr_SetString(PyExc_ValueError,
+				"compile(): unrecognised flags");
+		return NULL;
+	}
+	/* XXX Warn if (supplied_flags & PyCF_MASK_OBSOLETE) != 0? */
+
+	if (!dont_inherit) {
+		PyEval_MergeCompilerFlags(&cf);
+	}
+
+	if (PyAST_Check(cmd)) {
+		if (supplied_flags & PyCF_ONLY_AST) {
+			Py_INCREF(cmd);
+			result = cmd;
+		}
+		else {
+			PyArena *arena;
+			mod_ty mod;
+
+			arena = PyArena_New();
+			mod = PyAST_obj2mod(cmd, arena);
+			if (mod == NULL) {
+				PyArena_Free(arena);
+				return NULL;
+			}
+			result = (PyObject*)PyAST_Compile(mod, filename,
+							  &cf, arena);
+			PyArena_Free(arena);
+		}
+		return result;
+	}
+
 #ifdef Py_USING_UNICODE
 	if (PyUnicode_Check(cmd)) {
 		tmp = PyUnicode_AsUTF8String(cmd);
@@ -490,14 +526,7 @@ builtin_compile(PyObject *self, PyObject *args, PyObject *kwds)
 		cf.cf_flags |= PyCF_SOURCE_IS_UTF8;
 	}
 #endif
-	if (PyObject_AsReadBuffer(cmd, (const void **)&str, &length))
-		return NULL;
-	if ((size_t)length != strlen(str)) {
-		PyErr_SetString(PyExc_TypeError,
-				"compile() expected string without null bytes");
-		goto cleanup;
-	}
-
+	/* XXX: is it possible to pass start to the PyAST_ branch? */
 	if (strcmp(startstr, "exec") == 0)
 		start = Py_file_input;
 	else if (strcmp(startstr, "eval") == 0)
@@ -506,21 +535,17 @@ builtin_compile(PyObject *self, PyObject *args, PyObject *kwds)
 		start = Py_single_input;
 	else {
 		PyErr_SetString(PyExc_ValueError,
-		   "compile() arg 3 must be 'exec' or 'eval' or 'single'");
+				"compile() arg 3 must be 'exec'"
+				"or 'eval' or 'single'");
 		goto cleanup;
 	}
 
-	if (supplied_flags &
-	    ~(PyCF_MASK | PyCF_MASK_OBSOLETE | PyCF_DONT_IMPLY_DEDENT | PyCF_ONLY_AST))
-	{
-		PyErr_SetString(PyExc_ValueError,
-				"compile(): unrecognised flags");
+	if (PyObject_AsReadBuffer(cmd, (const void **)&str, &length))
+		goto cleanup;
+	if ((size_t)length != strlen(str)) {
+		PyErr_SetString(PyExc_TypeError,
+				"compile() expected string without null bytes");
 		goto cleanup;
-	}
-	/* XXX Warn if (supplied_flags & PyCF_MASK_OBSOLETE) != 0? */
-
-	if (!dont_inherit) {
-		PyEval_MergeCompilerFlags(&cf);
 	}
 	result = Py_CompileStringFlags(str, filename, start, &cf);
 cleanup:

Python/compile.c

@@ -2211,8 +2211,11 @@ unaryop(unaryop_ty op)
 		return UNARY_POSITIVE;
 	case USub:
 		return UNARY_NEGATIVE;
-	}
+	default:
+		PyErr_Format(PyExc_SystemError,
+			"unary op %d should not be possible", op);
 		return 0;
+	}
 }
 
 static int
@@ -2246,8 +2249,11 @@ binop(struct compiler *c, operator_ty op)
 		return BINARY_AND;
 	case FloorDiv:
 		return BINARY_FLOOR_DIVIDE;
-	}
+	default:
+		PyErr_Format(PyExc_SystemError,
+			"binary op %d should not be possible", op);
 		return 0;
+	}
 }
 
 static int
@@ -2274,8 +2280,9 @@ cmpop(cmpop_ty op)
 		return PyCmp_IN;
 	case NotIn:
 		return PyCmp_NOT_IN;
-	}
+	default:
 		return PyCmp_BAD;
+	}
 }
 
 static int
@@ -2309,10 +2316,11 @@ inplace_binop(struct compiler *c, operator_ty op)
 		return INPLACE_AND;
 	case FloorDiv:
 		return INPLACE_FLOOR_DIVIDE;
-	}
+	default:
 		PyErr_Format(PyExc_SystemError,
 			"inplace binary op %d should not be possible", op);
 		return 0;
+	}
 }
 
 static int