Implement PEP 238 in its (almost) full glory.

This introduces:

- A new operator // that means floor division (the kind of division
  where 1/2 is 0).

- The "future division" statement ("from __future__ import division)
  which changes the meaning of the / operator to implement "true
  division" (where 1/2 is 0.5).

- New overloadable operators __truediv__ and __floordiv__.

- New slots in the PyNumberMethods struct for true and floor division,
  new abstract APIs for them, new opcodes, and so on.

I emphasize that without the future division statement, the semantics
of / will remain unchanged until Python 3.0.

Not yet implemented are warnings (default off) when / is used with int
or long arguments.

This has been on display since 7/31 as SF patch #443474.

Flames to /dev/null.

Grammar/Grammar

@@ -38,7 +38,7 @@ stmt: simple_stmt | compound_stmt
 simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE
 small_stmt: expr_stmt | print_stmt  | del_stmt | pass_stmt | flow_stmt | import_stmt | global_stmt | exec_stmt | assert_stmt
 expr_stmt: testlist (augassign testlist | ('=' testlist)*)
-augassign: '+=' | '-=' | '*=' | '/=' | '%=' | '&=' | '|=' | '^=' | '<<=' | '>>=' | '**='
+augassign: '+=' | '-=' | '*=' | '/=' | '%=' | '&=' | '|=' | '^=' | '<<=' | '>>=' | '**=' | '//='
 # For normal assignments, additional restrictions enforced by the interpreter
 print_stmt: 'print' ( [ test (',' test)* [','] ] | '>>' test [ (',' test)+ [','] ] )
 del_stmt: 'del' exprlist
@@ -77,7 +77,7 @@ xor_expr: and_expr ('^' and_expr)*
 and_expr: shift_expr ('&' shift_expr)*
 shift_expr: arith_expr (('<<'|'>>') arith_expr)*
 arith_expr: term (('+'|'-') term)*
-term: factor (('*'|'/'|'%') factor)*
+term: factor (('*'|'/'|'%'|'//') factor)*
 factor: ('+'|'-'|'~') factor | power
 power: atom trailer* ('**' factor)*
 atom: '(' [testlist] ')' | '[' [listmaker] ']' | '{' [dictmaker] '}' | '`' testlist '`' | NAME | NUMBER | STRING+

Include/abstract.h

@@ -547,6 +547,26 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*/
 
        */
 
+     DL_IMPORT(PyObject *) PyNumber_FloorDivide(PyObject *o1, PyObject *o2);
+
+       /*
+	 Returns the result of dividing o1 by o2 giving an integral result,
+	 or null on failure.
+	 This is the equivalent of the Python expression: o1//o2.
+
+
+       */
+
+     DL_IMPORT(PyObject *) PyNumber_TrueDivide(PyObject *o1, PyObject *o2);
+
+       /*
+	 Returns the result of dividing o1 by o2 giving a float result,
+	 or null on failure.
+	 This is the equivalent of the Python expression: o1/o2.
+
+
+       */
+
      DL_IMPORT(PyObject *) PyNumber_Remainder(PyObject *o1, PyObject *o2);
 
        /*
@@ -742,6 +762,28 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*/
 
        */
 
+     DL_IMPORT(PyObject *) PyNumber_InPlaceFloorDivide(PyObject *o1,
+						       PyObject *o2);
+
+       /*
+	 Returns the result of dividing o1 by o2 giving an integral result,
+	 possibly in-place, or null on failure.
+	 This is the equivalent of the Python expression:
+	 o1 /= o2.
+
+       */
+
+     DL_IMPORT(PyObject *) PyNumber_InPlaceTrueDivide(PyObject *o1,
+						      PyObject *o2);
+
+       /*
+	 Returns the result of dividing o1 by o2 giving a float result,
+	 possibly in-place, or null on failure.
+	 This is the equivalent of the Python expression:
+	 o1 /= o2.
+
+       */
+
      DL_IMPORT(PyObject *) PyNumber_InPlaceRemainder(PyObject *o1, PyObject *o2);
 
        /*

Include/compile.h

@@ -41,6 +41,8 @@ typedef struct {
    effect, this passes on the "from __future__ import generators" state
    in effect when the code block was compiled. */
 #define CO_GENERATOR_ALLOWED    0x1000
+/* XXX Ditto for future division */
+#define CO_FUTURE_DIVISION    	0x2000
 
 extern DL_IMPORT(PyTypeObject) PyCode_Type;
 
@@ -64,6 +66,7 @@ typedef struct {
     int ff_last_lineno;
     int ff_nested_scopes;
     int ff_generators;
+    int ff_division;
 } PyFutureFeatures;
 
 DL_IMPORT(PyFutureFeatures *) PyNode_Future(struct _node *, char *);
@@ -76,6 +79,9 @@ DL_IMPORT(PyCodeObject *) PyNode_CompileFlags(struct _node *, char *,
 #define GENERATORS_DEFAULT 0
 #define FUTURE_GENERATORS "generators"
 
+#define DIVISION_DEFAULT 0
+#define FUTURE_DIVISION "division"
+
 /* for internal use only */
 #define _PyCode_GETCODEPTR(co, pp) \
 	((*(co)->co_code->ob_type->tp_as_buffer->bf_getreadbuffer) \

Include/object.h

@@ -161,6 +161,12 @@ typedef struct {
 	binaryfunc nb_inplace_and;
 	binaryfunc nb_inplace_xor;
 	binaryfunc nb_inplace_or;
+
+	/* The following require the Py_TPFLAGS_HAVE_CLASS flag */
+	binaryfunc nb_floor_divide;
+	binaryfunc nb_true_divide;
+	binaryfunc nb_inplace_floor_divide;
+	binaryfunc nb_inplace_true_divide;
 } PyNumberMethods;
 
 typedef struct {
@@ -396,7 +402,7 @@ given type object has a specified feature.
 /* tp_iter is defined */
 #define Py_TPFLAGS_HAVE_ITER (1L<<7)
 
-/* Experimental stuff for healing the type/class split */
+/* New members introduced by Python 2.2 exist */
 #define Py_TPFLAGS_HAVE_CLASS (1L<<8)
 
 /* Set if the type object is dynamically allocated */

Include/opcode.h

@@ -29,6 +29,10 @@ extern "C" {
 #define BINARY_ADD	23
 #define BINARY_SUBTRACT	24
 #define BINARY_SUBSCR	25
+#define BINARY_FLOOR_DIVIDE 26
+#define BINARY_TRUE_DIVIDE 27
+#define INPLACE_FLOOR_DIVIDE 28
+#define INPLACE_TRUE_DIVIDE 29
 
 #define SLICE		30
 /* Also uses 31-33 */

Include/pythonrun.h

@@ -12,6 +12,7 @@ extern "C" {
    accordingly then. */
 #define PyCF_NESTED_SCOPES	(0x00000001UL)
 #define PyCF_GENERATORS		(0x00000002UL)
+#define PyCF_DIVISION		(0x00000004UL)
 typedef struct {
 	unsigned long cf_flags;  /* bitmask of PyCF_xxx flags */
 } PyCompilerFlags;

Include/token.h

@@ -55,10 +55,12 @@ extern "C" {
 #define LEFTSHIFTEQUAL	45
 #define RIGHTSHIFTEQUAL	46
 #define DOUBLESTAREQUAL	47
+#define DOUBLESLASH	48
+#define DOUBLESLASHEQUAL 49
 /* Don't forget to update the table _PyParser_TokenNames in tokenizer.c! */
-#define OP		48
-#define ERRORTOKEN	49
-#define N_TOKENS	50
+#define OP		50
+#define ERRORTOKEN	51
+#define N_TOKENS	52
 
 /* Special definitions for cooperation with parser */
 

Lib/__future__.py

@@ -68,3 +68,4 @@ def __repr__(self):
 
 nested_scopes = _Feature((2, 1, 0, "beta", 1), (2, 2, 0, "alpha", 0))
 generators = _Feature((2, 2, 0, "alpha", 1), (2, 3, 0, "final", 0))
+division = _Feature((2, 2, 0, "alpha", 2), (3, 0, 0, "alpha", 0))

Objects/abstract.c

@@ -564,6 +564,20 @@ PyNumber_Add(PyObject *v, PyObject *w)
 	return result;
 }
 
+PyObject *
+PyNumber_FloorDivide(PyObject *v, PyObject *w)
+{
+	/* XXX tp_flags test */
+	return binary_op(v, w, NB_SLOT(nb_floor_divide), "//");
+}
+
+PyObject *
+PyNumber_TrueDivide(PyObject *v, PyObject *w)
+{
+	/* XXX tp_flags test */
+	return binary_op(v, w, NB_SLOT(nb_true_divide), "/");
+}
+
 PyObject *
 PyNumber_Remainder(PyObject *v, PyObject *w)
 {
@@ -630,6 +644,22 @@ INPLACE_BINOP(PyNumber_InPlaceRshift, nb_inplace_rshift, nb_rshift, ">>=")
 INPLACE_BINOP(PyNumber_InPlaceSubtract, nb_inplace_subtract, nb_subtract, "-=")
 INPLACE_BINOP(PyNumber_InPlaceDivide, nb_inplace_divide, nb_divide, "/=")
 
+PyObject *
+PyNumber_InPlaceFloorDivide(PyObject *v, PyObject *w)
+{
+	/* XXX tp_flags test */
+	return binary_iop(v, w, NB_SLOT(nb_inplace_floor_divide),
+			  NB_SLOT(nb_floor_divide), "//=");
+}
+
+PyObject *
+PyNumber_InPlaceTrueDivide(PyObject *v, PyObject *w)
+{
+	/* XXX tp_flags test */
+	return binary_iop(v, w, NB_SLOT(nb_inplace_true_divide),
+			  NB_SLOT(nb_true_divide), "/=");
+}
+
 PyObject *
 PyNumber_InPlaceAdd(PyObject *v, PyObject *w)
 {

Objects/classobject.c

@@ -1435,6 +1435,8 @@ BINARY(instance_mul, "mul", PyNumber_Multiply)
 BINARY(instance_div, "div", PyNumber_Divide)
 BINARY(instance_mod, "mod", PyNumber_Remainder)
 BINARY(instance_divmod, "divmod", PyNumber_Divmod)
+BINARY(instance_floordiv, "floordiv", PyNumber_FloorDivide)
+BINARY(instance_truediv, "truediv", PyNumber_TrueDivide)
 
 BINARY_INPLACE(instance_ior, "or", PyNumber_InPlaceOr)
 BINARY_INPLACE(instance_ixor, "xor", PyNumber_InPlaceXor)
@@ -1446,6 +1448,8 @@ BINARY_INPLACE(instance_isub, "sub", PyNumber_InPlaceSubtract)
 BINARY_INPLACE(instance_imul, "mul", PyNumber_InPlaceMultiply)
 BINARY_INPLACE(instance_idiv, "div", PyNumber_InPlaceDivide)
 BINARY_INPLACE(instance_imod, "mod", PyNumber_InPlaceRemainder)
+BINARY_INPLACE(instance_ifloordiv, "floordiv", PyNumber_InPlaceFloorDivide)
+BINARY_INPLACE(instance_itruediv, "truediv", PyNumber_InPlaceTrueDivide)
 
 /* Try a 3-way comparison, returning an int; v is an instance.  Return:
    -2 for an exception;
@@ -1900,6 +1904,10 @@ static PyNumberMethods instance_as_number = {
 	(binaryfunc)instance_iand,		/* nb_inplace_and */
 	(binaryfunc)instance_ixor,		/* nb_inplace_xor */
 	(binaryfunc)instance_ior,		/* nb_inplace_or */
+	(binaryfunc)instance_floordiv,		/* nb_floor_divide */
+	(binaryfunc)instance_truediv,		/* nb_true_divide */
+	(binaryfunc)instance_ifloordiv,		/* nb_inplace_floor_divide */
+	(binaryfunc)instance_itruediv,		/* nb_inplace_true_divide */
 };
 
 PyTypeObject PyInstance_Type = {

Objects/complexobject.c

@@ -441,6 +441,21 @@ complex_pow(PyComplexObject *v, PyObject *w, PyComplexObject *z)
 	return PyComplex_FromCComplex(p);
 }
 
+static PyObject *
+complex_int_div(PyComplexObject *v, PyComplexObject *w)
+{
+	PyObject *t, *r;
+
+	t = complex_divmod(v, w);
+	if (t != NULL) {
+		r = PyTuple_GET_ITEM(t, 0);
+		Py_INCREF(r);
+		Py_DECREF(t);
+		return r;
+	}
+	return NULL;
+}
+
 static PyObject *
 complex_neg(PyComplexObject *v)
 {
@@ -859,6 +874,21 @@ static PyNumberMethods complex_as_number = {
 	(unaryfunc)complex_float,		/* nb_float */
 	0,					/* nb_oct */
 	0,					/* nb_hex */
+	0,					/* nb_inplace_add */
+	0,					/* nb_inplace_subtract */
+	0,					/* nb_inplace_multiply*/
+	0,					/* nb_inplace_divide */
+	0,					/* nb_inplace_remainder */
+	0, 					/* nb_inplace_power */
+	0,					/* nb_inplace_lshift */
+	0,					/* nb_inplace_rshift */
+	0,					/* nb_inplace_and */
+	0,					/* nb_inplace_xor */
+	0,					/* nb_inplace_or */
+	(binaryfunc)complex_int_div,		/* nb_floor_divide */
+	(binaryfunc)complex_div,		/* nb_true_divide */
+	0,					/* nb_inplace_floor_divide */
+	0,					/* nb_inplace_true_divide */
 };
 
 PyTypeObject PyComplex_Type = {

Objects/floatobject.c

@@ -557,6 +557,21 @@ float_pow(PyObject *v, PyObject *w, PyObject *z)
 	return PyFloat_FromDouble(ix);
 }
 
+static PyObject *
+float_int_div(PyObject *v, PyObject *w)
+{
+	PyObject *t, *r;
+
+	t = float_divmod(v, w);
+	if (t != NULL) {
+		r = PyTuple_GET_ITEM(t, 0);
+		Py_INCREF(r);
+		Py_DECREF(t);
+		return r;
+	}
+	return NULL;
+}
+
 static PyObject *
 float_neg(PyFloatObject *v)
 {
@@ -678,19 +693,23 @@ static PyNumberMethods float_as_number = {
 	(unaryfunc)float_int, /*nb_int*/
 	(unaryfunc)float_long, /*nb_long*/
 	(unaryfunc)float_float, /*nb_float*/
-	0,		/*nb_oct*/
-	0,		/*nb_hex*/
-	0,		/*nb_inplace_add*/
-	0,		/*nb_inplace_subtract*/
-	0,		/*nb_inplace_multiply*/
-	0,		/*nb_inplace_divide*/
-	0,		/*nb_inplace_remainder*/
-	0, 		/*nb_inplace_power*/
-	0,		/*nb_inplace_lshift*/
-	0,		/*nb_inplace_rshift*/
-	0,		/*nb_inplace_and*/
-	0,		/*nb_inplace_xor*/
-	0,		/*nb_inplace_or*/
+	0,		/* nb_oct */
+	0,		/* nb_hex */
+	0,		/* nb_inplace_add */
+	0,		/* nb_inplace_subtract */
+	0,		/* nb_inplace_multiply */
+	0,		/* nb_inplace_divide */
+	0,		/* nb_inplace_remainder */
+	0, 		/* nb_inplace_power */
+	0,		/* nb_inplace_lshift */
+	0,		/* nb_inplace_rshift */
+	0,		/* nb_inplace_and */
+	0,		/* nb_inplace_xor */
+	0,		/* nb_inplace_or */
+	float_int_div,	/* nb_floor_divide */
+	float_div,	/* nb_true_divide */
+	0,		/* nb_inplace_floor_divide */
+	0,		/* nb_inplace_true_divide */
 };
 
 PyTypeObject PyFloat_Type = {

Objects/intobject.c

@@ -702,6 +702,12 @@ int_or(PyIntObject *v, PyIntObject *w)
 	return PyInt_FromLong(a | b);
 }
 
+static PyObject *
+int_true_divide(PyObject *v, PyObject *w)
+{
+	return PyFloat_Type.tp_as_number->nb_divide(v, w);
+}
+
 static PyObject *
 int_int(PyIntObject *v)
 {
@@ -812,6 +818,10 @@ static PyNumberMethods int_as_number = {
 	0,			/*nb_inplace_and*/
 	0,			/*nb_inplace_xor*/
 	0,			/*nb_inplace_or*/
+	(binaryfunc)int_div,	/* nb_floor_divide */
+	int_true_divide,	/* nb_true_divide */
+	0,			/* nb_inplace_floor_divide */
+	0,			/* nb_inplace_true_divide */
 };
 
 PyTypeObject PyInt_Type = {