diff -r aba7d1f2d2a9 Lib/test/test_unicode.py
--- a/Lib/test/test_unicode.py	Fri May 06 18:49:52 2011 +0200
+++ b/Lib/test/test_unicode.py	Tue May 10 15:06:44 2011 -0700
@@ -550,6 +550,8 @@
         self.assertEqual("{0[foo-bar]}".format({'foo-bar':'baz'}), 'baz')
         self.assertEqual("{0[foo bar]}".format({'foo bar':'baz'}), 'baz')
         self.assertEqual("{0[ ]}".format({' ':3}), '3')
+        self.assertEqual("{0[{]}".format({'{':3}), '3')
+        self.assertEqual("{0[!]}".format({'!':3}), '3')
 
         self.assertEqual('{foo._x}'.format(foo=C(20)), '20')
         self.assertEqual('{1}{0}'.format(D(10), D(20)), '2010')
diff -r aba7d1f2d2a9 Objects/stringlib/string_format.h
--- a/Objects/stringlib/string_format.h	Fri May 06 18:49:52 2011 +0200
+++ b/Objects/stringlib/string_format.h	Tue May 10 15:06:44 2011 -0700
@@ -628,6 +628,37 @@
     return ok;
 }
 
+
+void 
+advance_beyond_field(SubString *str)
+{
+    if (str->ptr > str->end) return;
+    switch (*++str->ptr) {
+    case '[':
+        while(str->ptr < str->end && *(str->ptr) != ']') 
+            str->ptr++;
+        advance_beyond_field(str);
+        break;
+    case '.':
+        while(str->ptr < str->end)
+            switch(*++str->ptr) {
+            case ':':
+            case '!':
+                str->ptr--;
+                return;
+            case '[':
+                advance_beyond_field(str);
+                str->ptr--;
+                break;
+            default:
+                continue;
+            }
+        break;
+    default:
+        return;
+    }       
+}
+
 static int
 parse_field(SubString *str, SubString *field_name, SubString *format_spec,
             STRINGLIB_CHAR *conversion)
@@ -647,6 +678,11 @@
     field_name->ptr = str->ptr;
     while (str->ptr < str->end) {
         switch (c = *(str->ptr++)) {
+        case '.':
+        case '[':
+            str->ptr -= 2;
+            advance_beyond_field(str);
+            continue;
         case ':':
         case '!':
             break;
@@ -726,6 +762,7 @@
     STRINGLIB_CHAR c = 0;
     STRINGLIB_CHAR *start;
     int count;
+    int bracket_significant = 1;
     Py_ssize_t len;
     int markup_follows = 0;
 
@@ -806,6 +843,17 @@
        about that case */
     while (self->str.ptr < self->str.end) {
         switch (c = *(self->str.ptr++)) {
+        case '[':
+            if (bracket_significant) {
+                while (self->str.ptr < self->str.end-1 && *self->str.ptr != ']') {
+                    self->str.ptr++;
+                }
+            }
+            continue;
+        case ':':
+        case '!':
+            bracket_significant = 0;
+            continue;
         case '{':
             /* the format spec needs to be recursively expanded.
                this is an optimization, and not strictly needed */