[Python-Dev] Changes in semantics to str()?

Sept. 30, 2000

      When we changed floats to behave different on repr() than on str(), we
briefly discussed changes to the container objects as well, but
nothing came of it.

Currently, str() of a tuple, list or dictionary is the same as repr()
of those objects.  This is not very consistent.  For example, when we
have a float like 1.1 which can't be represented exactly, str() yields
"1.1" but repr() yields "1.1000000000000001".  But if we place the
same number in a list, it doesn't matter which function we use: we
always get "[1.1000000000000001]".

Below I have included changes to listobject.c, tupleobject.c and
dictobject.c that fix this.  The fixes change the print and str()
callbacks for these objects to use PyObject_Str() on the contained
items -- except if the item is a string or Unicode string.  I made
these exceptions because I don't like the idea of str(["abc"])
yielding [abc] -- I'm too used to the idea of seeing ['abc'] here.
And str() of a Unicode object fails when it contains non-ASCII
characters, so that's no good either -- it would break too much code.

Is it too late to check this in?  Another negative consequence would
be that for user-defined or 3rd party extension objects that have
different repr() and str(), like NumPy arrays, it might break some
code -- but I think this is not very likely.

--Guido van Rossum (home page: http://www.python.org/~guido/)

*** dictobject.c	2000/09/01 23:29:27	2.65
--- dictobject.c	2000/09/30 16:03:04
***************
*** 594,599 ****
--- 594,601 ----
  	register int i;
  	register int any;
  	register dictentry *ep;
+ 	PyObject *item;
+ 	int itemflags;

  	i = Py_ReprEnter((PyObject*)mp);
  	if (i != 0) {
***************
*** 609,620 ****
  		if (ep->me_value != NULL) {
  			if (any++ > 0)
  				fprintf(fp, ", ");
! 			if (PyObject_Print((PyObject *)ep->me_key, fp, 0)!=0) {
  				Py_ReprLeave((PyObject*)mp);
  				return -1;
  			}
  			fprintf(fp, ": ");
! 			if (PyObject_Print(ep->me_value, fp, 0) != 0) {
  				Py_ReprLeave((PyObject*)mp);
  				return -1;
  			}
--- 611,630 ----
  		if (ep->me_value != NULL) {
  			if (any++ > 0)
  				fprintf(fp, ", ");
! 			item = (PyObject *)ep->me_key;
! 			itemflags = flags;
! 			if (item == NULL || PyString_Check(item) || PyUnicode_Check(item))
! 				itemflags = 0;
! 			if (PyObject_Print(item, fp, itemflags)!=0) {
  				Py_ReprLeave((PyObject*)mp);
  				return -1;
  			}
  			fprintf(fp, ": ");
! 			item = ep->me_value;
! 			itemflags = flags;
! 			if (item == NULL || PyString_Check(item) || PyUnicode_Check(item))
! 				itemflags = 0;
! 			if (PyObject_Print(item, fp, itemflags) != 0) {
  				Py_ReprLeave((PyObject*)mp);
  				return -1;
  			}
***************
*** 661,666 ****
--- 671,722 ----
  	return v;
  }

+ static PyObject *
+ dict_str(dictobject *mp)
+ {
+ 	auto PyObject *v;
+ 	PyObject *sepa, *colon, *item, *repr;
+ 	register int i;
+ 	register int any;
+ 	register dictentry *ep;
+ 
+ 	i = Py_ReprEnter((PyObject*)mp);
+ 	if (i != 0) {
+ 		if (i > 0)
+ 			return PyString_FromString("{...}");
+ 		return NULL;
+ 	}
+ 
+ 	v = PyString_FromString("{");
+ 	sepa = PyString_FromString(", ");
+ 	colon = PyString_FromString(": ");
+ 	any = 0;
+ 	for (i = 0, ep = mp->ma_table; i < mp->ma_size && v; i++, ep++) {
+ 		if (ep->me_value != NULL) {
+ 			if (any++)
+ 				PyString_Concat(&v, sepa);
+ 			item = ep->me_key;
+ 			if (item == NULL || PyString_Check(item) || PyUnicode_Check(item))
+ 				repr = PyObject_Repr(item);
+ 			else
+ 				repr = PyObject_Str(item);
+ 			PyString_ConcatAndDel(&v, repr);
+ 			PyString_Concat(&v, colon);
+ 			item = ep->me_value;
+ 			if (item == NULL || PyString_Check(item) || PyUnicode_Check(item))
+ 				repr = PyObject_Repr(item);
+ 			else
+ 				repr = PyObject_Str(item);
+ 			PyString_ConcatAndDel(&v, repr);
+ 		}
+ 	}
+ 	PyString_ConcatAndDel(&v, PyString_FromString("}"));
+ 	Py_ReprLeave((PyObject*)mp);
+ 	Py_XDECREF(sepa);
+ 	Py_XDECREF(colon);
+ 	return v;
+ }
+ 
  static int
  dict_length(dictobject *mp)
  {
***************
*** 1193,1199 ****
  	&dict_as_mapping,	/*tp_as_mapping*/
  	0,		/* tp_hash */
  	0,		/* tp_call */
! 	0,		/* tp_str */
  	0,		/* tp_getattro */
  	0,		/* tp_setattro */
  	0,		/* tp_as_buffer */
--- 1249,1255 ----
  	&dict_as_mapping,	/*tp_as_mapping*/
  	0,		/* tp_hash */
  	0,		/* tp_call */
! 	(reprfunc)dict_str, /* tp_str */
  	0,		/* tp_getattro */
  	0,		/* tp_setattro */
  	0,		/* tp_as_buffer */
Index: listobject.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Objects/listobject.c,v
retrieving revision 2.88
diff -c -r2.88 listobject.c
*** listobject.c	2000/09/26 05:46:01	2.88
--- listobject.c	2000/09/30 16:03:04
***************
*** 197,203 ****
  static int
  list_print(PyListObject *op, FILE *fp, int flags)
  {
! 	int i;

  	i = Py_ReprEnter((PyObject*)op);
  	if (i != 0) {
--- 197,204 ----
  static int
  list_print(PyListObject *op, FILE *fp, int flags)
  {
! 	int i, itemflags;
! 	PyObject *item;

  	i = Py_ReprEnter((PyObject*)op);
  	if (i != 0) {
***************
*** 210,216 ****
  	for (i = 0; i < op->ob_size; i++) {
  		if (i > 0)
  			fprintf(fp, ", ");
! 		if (PyObject_Print(op->ob_item[i], fp, 0) != 0) {
  			Py_ReprLeave((PyObject *)op);
  			return -1;
  		}
--- 211,221 ----
  	for (i = 0; i < op->ob_size; i++) {
  		if (i > 0)
  			fprintf(fp, ", ");
! 		item = op->ob_item[i];
! 		itemflags = flags;
! 		if (item == NULL || PyString_Check(item) || PyUnicode_Check(item))
! 			itemflags = 0;
! 		if (PyObject_Print(item, fp, itemflags) != 0) {
  			Py_ReprLeave((PyObject *)op);
  			return -1;
  		}
***************
*** 245,250 ****
--- 250,285 ----
  	return s;
  }

+ static PyObject *
+ list_str(PyListObject *v)
+ {
+ 	PyObject *s, *comma, *item, *repr;
+ 	int i;
+ 
+ 	i = Py_ReprEnter((PyObject*)v);
+ 	if (i != 0) {
+ 		if (i > 0)
+ 			return PyString_FromString("[...]");
+ 		return NULL;
+ 	}
+ 	s = PyString_FromString("[");
+ 	comma = PyString_FromString(", ");
+ 	for (i = 0; i < v->ob_size && s != NULL; i++) {
+ 		if (i > 0)
+ 			PyString_Concat(&s, comma);
+ 		item = v->ob_item[i];
+ 		if (item == NULL || PyString_Check(item) || PyUnicode_Check(item))
+ 			repr = PyObject_Repr(item);
+ 		else
+ 			repr = PyObject_Str(item);
+ 		PyString_ConcatAndDel(&s, repr);
+ 	}
+ 	Py_XDECREF(comma);
+ 	PyString_ConcatAndDel(&s, PyString_FromString("]"));
+ 	Py_ReprLeave((PyObject *)v);
+ 	return s;
+ }
+ 
  static int
  list_compare(PyListObject *v, PyListObject *w)
  {
***************
*** 1484,1490 ****
  	0,		/*tp_as_mapping*/
  	0,		/*tp_hash*/
  	0,		/*tp_call*/
! 	0,		/*tp_str*/
  	0,		/*tp_getattro*/
  	0,		/*tp_setattro*/
  	0,		/*tp_as_buffer*/
--- 1519,1525 ----
  	0,		/*tp_as_mapping*/
  	0,		/*tp_hash*/
  	0,		/*tp_call*/
! 	(reprfunc)list_str, /*tp_str*/
  	0,		/*tp_getattro*/
  	0,		/*tp_setattro*/
  	0,		/*tp_as_buffer*/
***************
*** 1561,1567 ****
  	0,		/*tp_as_mapping*/
  	0,		/*tp_hash*/
  	0,		/*tp_call*/
! 	0,		/*tp_str*/
  	0,		/*tp_getattro*/
  	0,		/*tp_setattro*/
  	0,		/*tp_as_buffer*/
--- 1596,1602 ----
  	0,		/*tp_as_mapping*/
  	0,		/*tp_hash*/
  	0,		/*tp_call*/
! 	(reprfunc)list_str, /*tp_str*/
  	0,		/*tp_getattro*/
  	0,		/*tp_setattro*/
  	0,		/*tp_as_buffer*/
Index: tupleobject.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Objects/tupleobject.c,v
retrieving revision 2.46
diff -c -r2.46 tupleobject.c
*** tupleobject.c	2000/09/15 07:32:39	2.46
--- tupleobject.c	2000/09/30 16:03:04
***************
*** 167,178 ****
  static int
  tupleprint(PyTupleObject *op, FILE *fp, int flags)
  {
! 	int i;
  	fprintf(fp, "(");
  	for (i = 0; i < op->ob_size; i++) {
  		if (i > 0)
  			fprintf(fp, ", ");
! 		if (PyObject_Print(op->ob_item[i], fp, 0) != 0)
  			return -1;
  	}
  	if (op->ob_size == 1)
--- 167,183 ----
  static int
  tupleprint(PyTupleObject *op, FILE *fp, int flags)
  {
! 	int i, itemflags;
! 	PyObject *item;
  	fprintf(fp, "(");
  	for (i = 0; i < op->ob_size; i++) {
  		if (i > 0)
  			fprintf(fp, ", ");
! 		item = op->ob_item[i];
! 		itemflags = flags;
! 		if (item == NULL || PyString_Check(item) || PyUnicode_Check(item))
! 			itemflags = 0;
! 		if (PyObject_Print(item, fp, itemflags) != 0)
  			return -1;
  	}
  	if (op->ob_size == 1)
***************
*** 200,205 ****
--- 205,234 ----
  	return s;
  }

+ static PyObject *
+ tuplestr(PyTupleObject *v)
+ {
+ 	PyObject *s, *comma, *item, *repr;
+ 	int i;
+ 	s = PyString_FromString("(");
+ 	comma = PyString_FromString(", ");
+ 	for (i = 0; i < v->ob_size && s != NULL; i++) {
+ 		if (i > 0)
+ 			PyString_Concat(&s, comma);
+ 		item = v->ob_item[i];
+ 		if (item == NULL || PyString_Check(item) || PyUnicode_Check(item))
+ 			repr = PyObject_Repr(item);
+ 		else
+ 			repr = PyObject_Str(item);
+ 		PyString_ConcatAndDel(&s, repr);
+ 	}
+ 	Py_DECREF(comma);
+ 	if (v->ob_size == 1)
+ 		PyString_ConcatAndDel(&s, PyString_FromString(","));
+ 	PyString_ConcatAndDel(&s, PyString_FromString(")"));
+ 	return s;
+ }
+ 
  static int
  tuplecompare(register PyTupleObject *v, register PyTupleObject *w)
  {
***************
*** 412,418 ****
  	0,		/*tp_as_mapping*/
  	(hashfunc)tuplehash, /*tp_hash*/
  	0,		/*tp_call*/
! 	0,		/*tp_str*/
  	0,		/*tp_getattro*/
  	0,		/*tp_setattro*/
  	0,		/*tp_as_buffer*/
--- 441,447 ----
  	0,		/*tp_as_mapping*/
  	(hashfunc)tuplehash, /*tp_hash*/
  	0,		/*tp_call*/
! 	(reprfunc)tuplestr, /*tp_str*/
  	0,		/*tp_getattro*/
  	0,		/*tp_setattro*/
  	0,		/*tp_as_buffer*/