Fix for SF bug #415514: "%#x" % 0 caused assertion failure/abort.

http://sourceforge.net/tracker/index.php?func=detail&aid=415514&group_id=5470&atid=105470
For short ints, Python defers to the platform C library to figure out what
%#x should do.  The code asserted that the platform C returned a string
beginning with "0x".  However, that's not true when-- and only when --the
*value* being formatted is 0.  Changed the code to live with C's inconsistency
here.  In the meantime, the problem does not arise if you format a long 0 (0L)
instead.  However, that's because the code *we* wrote to do %#x conversions on
longs produces a leading "0x" regardless of value.  That's probably wrong too:
we should drop leading "0x", for consistency with C, when (& only when) formatting
0L.  So I changed the long formatting code to do that too.

2 files changed, 37 insertions, 25 deletions

diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index 740cbe2..8e11536 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -2575,8 +2575,16 @@ _PyString_FormatLong(PyObject *val, int flags, int prec, int type,
 	numdigits = len - numnondigits;
 	assert(numdigits > 0);
 
-	/* Get rid of base marker unless F_ALT */
-	if ((flags & F_ALT) == 0) {
+	/* Get rid of base marker unless F_ALT.  Even if F_ALT, leading 0x
+	 * must be stripped if the *value* is 0.
+	 */
+	if ((flags & F_ALT) == 0 ||
+	    ((flags & F_ALT) &&
+	     (type == 'x' || type == 'X') &&
+	     numdigits == 1 &&
+	     !sign &&
+	     buf[2] == '0'
+	    )) {
 		/* Need to skip 0x, 0X or 0. */
 		int skipped = 0;
 		switch (type) {
@@ -3015,17 +3023,21 @@ PyString_Format(PyObject *format, PyObject *args)
 					width--;
 			}
 			if ((flags & F_ALT) && (c == 'x' || c == 'X')) {
+				/* There's a base marker ("0x" or "0X") if and
+				 * only if the value is non-zero.
+				 */
 				assert(pbuf[0] == '0');
-				assert(pbuf[1] == c);
-				if (fill != ' ') {
-					*res++ = *pbuf++;
-					*res++ = *pbuf++;
+				if (pbuf[1] == c) {
+					if (fill != ' ') {
+						*res++ = *pbuf++;
+						*res++ = *pbuf++;
+					}
+					rescnt -= 2;
+					width -= 2;
+					if (width < 0)
+						width = 0;
+					len -= 2;
 				}
-				rescnt -= 2;
-				width -= 2;
-				if (width < 0)
-					width = 0;
-				len -= 2;
 			}
 			if (width > len && !(flags & F_LJUST)) {
 				do {
@@ -3037,9 +3049,8 @@ PyString_Format(PyObject *format, PyObject *args)
 				if (sign)
 					*res++ = sign;
 				if ((flags & F_ALT) &&
-				    (c == 'x' || c == 'X')) {
-					assert(pbuf[0] == '0');
-					assert(pbuf[1] == c);
+				    (c == 'x' || c == 'X') &&
+				    pbuf[1] == c) {
 					*res++ = *pbuf++;
 					*res++ = *pbuf++;
 				}
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index c237789..aecc261 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -5081,16 +5081,17 @@ PyObject *PyUnicode_Format(PyObject *format,
 	    }
 	    if ((flags & F_ALT) && (c == 'x' || c == 'X')) {
 		assert(pbuf[0] == '0');
-		assert(pbuf[1] == c);
-		if (fill != ' ') {
-		    *res++ = *pbuf++;
-		    *res++ = *pbuf++;
+		if (pbuf[1] == c) {
+			if (fill != ' ') {
+			    *res++ = *pbuf++;
+			    *res++ = *pbuf++;
+			}
+			rescnt -= 2;
+			width -= 2;
+			if (width < 0)
+			    width = 0;
+			len -= 2;
 		}
-		rescnt -= 2;
-		width -= 2;
-		if (width < 0)
-		    width = 0;
-		len -= 2;
 	    }
 	    if (width > len && !(flags & F_LJUST)) {
 		do {
@@ -5101,9 +5102,9 @@ PyObject *PyUnicode_Format(PyObject *format,
 	    if (fill == ' ') {
 		if (sign)
 		    *res++ = sign;
-		if ((flags & F_ALT) && (c == 'x' || c == 'X')) {
+		if ((flags & F_ALT) && (c == 'x' || c == 'X') &&
+		    pbuf[1] == c) {
 		    assert(pbuf[0] == '0');
-		    assert(pbuf[1] == c);
 		    *res++ = *pbuf++;
 		    *res++ = *pbuf++;
 		}