Added ',' thousands grouping to int.__format__. See PEP 378.

This is incomplete, but I want to get some version into the next alpha. I am still working on:
Documentation.
More tests.
Implement for floats.

In addition, there's an existing bug with 'n' formatting that carries forward to thousands grouping (issue 5515).

Include/bytesobject.h

@@ -91,13 +91,25 @@ PyAPI_FUNC(int) PyBytes_AsStringAndSize(
    into the string pointed to by buffer.  For the argument descriptions,
    see Objects/stringlib/localeutil.h */
 
-PyAPI_FUNC(int) _PyBytes_InsertThousandsGrouping(char *buffer,
+PyAPI_FUNC(int) _PyBytes_InsertThousandsGroupingLocale(char *buffer,
 						  Py_ssize_t n_buffer,
 						  Py_ssize_t n_digits,
 						  Py_ssize_t buf_size,
 						  Py_ssize_t *count,
 						  int append_zero_char);
 
+/* Using explicit passed-in values, insert the thousands grouping
+   into the string pointed to by buffer.  For the argument descriptions,
+   see Objects/stringlib/localeutil.h */
+PyAPI_FUNC(int) _PyBytes_InsertThousandsGrouping(char *buffer,
+						 Py_ssize_t n_buffer,
+						 Py_ssize_t n_digits,
+						 Py_ssize_t buf_size,
+						 Py_ssize_t *count,
+                                                 int append_zero_char,
+                                                 const char *grouping,
+                                                 const char *thousands_sep);
+
 /* Flags used by string formatting */
 #define F_LJUST (1<<0)
 #define F_SIGN	(1<<1)

Include/unicodeobject.h

@@ -1482,13 +1482,24 @@ PyAPI_FUNC(PyObject *) _PyUnicode_XStrip(
    into the string pointed to by buffer.  For the argument descriptions,
    see Objects/stringlib/localeutil.h */
 
-PyAPI_FUNC(int) _PyUnicode_InsertThousandsGrouping(Py_UNICODE *buffer,
+PyAPI_FUNC(int) _PyUnicode_InsertThousandsGroupingLocale(Py_UNICODE *buffer,
 						  Py_ssize_t n_buffer,
 						  Py_ssize_t n_digits,
 						  Py_ssize_t buf_size,
 						  Py_ssize_t *count,
 						  int append_zero_char);
 
+/* Using explicit passed-in values, insert the thousands grouping
+   into the string pointed to by buffer.  For the argument descriptions,
+   see Objects/stringlib/localeutil.h */
+PyAPI_FUNC(int) _PyUnicode_InsertThousandsGrouping(Py_UNICODE *buffer,
+						 Py_ssize_t n_buffer,
+						 Py_ssize_t n_digits,
+						 Py_ssize_t buf_size,
+						 Py_ssize_t *count,
+                                                 int append_zero_char,
+                                                 const char *grouping,
+                                                 const char *thousands_sep);
 /* === Characters Type APIs =============================================== */
 
 /* Helper array used by Py_UNICODE_ISSPACE(). */

Lib/test/test_types.py

@@ -338,6 +338,15 @@ class TypesTests(unittest.TestCase):
         test(123456, "#012X", '0X000001E240')
         test(-123456, "#012X", '-0X00001E240')
 
+        test(123, ',', '123')
+        test(-123, ',', '-123')
+        test(1234, ',', '1,234')
+        test(-1234, ',', '-1,234')
+        test(123456, ',', '123,456')
+        test(-123456, ',', '-123,456')
+        test(1234567, ',', '1,234,567')
+        test(-1234567, ',', '-1,234,567')
+
         # make sure these are errors
 
         # precision disallowed
@@ -347,6 +356,8 @@ class TypesTests(unittest.TestCase):
         # format spec must be string
         self.assertRaises(TypeError, 3 .__format__, None)
         self.assertRaises(TypeError, 3 .__format__, 0)
+        # can't have ',' with 'n'
+        self.assertRaises(ValueError, 3 .__format__, ",n")
 
         # ensure that only int and float type specifiers work
         for format_spec in ([chr(x) for x in range(ord('a'), ord('z')+1)] +

Objects/bytesobject.c

@@ -583,6 +583,7 @@ PyBytes_AsStringAndSize(register PyObject *obj,
 #include "stringlib/transmogrify.h"
 
 #define _Py_InsertThousandsGrouping _PyBytes_InsertThousandsGrouping
+#define _Py_InsertThousandsGroupingLocale _PyBytes_InsertThousandsGroupingLocale
 #include "stringlib/localeutil.h"
 
 PyObject *

Objects/stringlib/formatter.h

@@ -120,6 +120,7 @@ typedef struct {
     int alternate;
     STRINGLIB_CHAR sign;
     Py_ssize_t width;
+    int thousands_separators;
     Py_ssize_t precision;
     STRINGLIB_CHAR type;
 } InternalFormatSpec;
@@ -149,6 +150,7 @@ parse_internal_render_format_spec(STRINGLIB_CHAR *format_spec,
     format->alternate = 0;
     format->sign = '\0';
     format->width = -1;
+    format->thousands_separators = 0;
     format->precision = -1;
     format->type = default_type;
 
@@ -201,6 +203,12 @@ parse_internal_render_format_spec(STRINGLIB_CHAR *format_spec,
         format->width = -1;
     }
 
+    /* Comma signifies add thousands separators */
+    if (end-ptr && ptr[0] == ',') {
+        format->thousands_separators = 1;
+        ++ptr;
+    }
+
     /* Parse field precision */
     if (end-ptr && ptr[0] == '.') {
         ++ptr;
@@ -230,6 +238,11 @@ parse_internal_render_format_spec(STRINGLIB_CHAR *format_spec,
         ++ptr;
     }
 
+    if (format->type == 'n' && format->thousands_separators) {
+        PyErr_Format(PyExc_ValueError, "Cannot specify ',' with 'n'.");
+        return 0;
+    }
+
     return 1;
 }
 
@@ -630,8 +643,13 @@ format_int_or_long_internal(PyObject *value, const InternalFormatSpec *format,
     if (format->type == 'n')
             /* Compute how many additional chars we need to allocate
                to hold the thousands grouping. */
-            STRINGLIB_GROUPING(NULL, n_digits, n_digits,
+            STRINGLIB_GROUPING_LOCALE(NULL, n_digits, n_digits,
                                0, &n_grouping_chars, 0);
+    if (format->thousands_separators)
+            /* Compute how many additional chars we need to allocate
+               to hold the thousands grouping. */
+            STRINGLIB_GROUPING(NULL, n_digits, n_digits,
+                               0, &n_grouping_chars, 0, "\3", ",");
 
     /* Calculate the widths of the various leading and trailing parts */
     calc_number_widths(&spec, sign, n_prefix, n_digits + n_grouping_chars,
@@ -670,11 +688,22 @@ format_int_or_long_internal(PyObject *value, const InternalFormatSpec *format,
                reserved enough space. */
             STRINGLIB_CHAR *pstart = p + n_leading_chars;
 #ifndef NDEBUG
-            int r =
+            int r;
 #endif
-                STRINGLIB_GROUPING(pstart, n_digits, n_digits,
+            if (format->type == 'n')
+#ifndef NDEBUG
+                r = 
+#endif
+                    STRINGLIB_GROUPING_LOCALE(pstart, n_digits, n_digits,
                            spec.n_total+n_grouping_chars-n_leading_chars,
                            NULL, 0);
+            else
+#ifndef NDEBUG
+                r =
+                    STRINGLIB_GROUPING(pstart, n_digits, n_digits,
+                           spec.n_total+n_grouping_chars-n_leading_chars,
+                           NULL, 0, "\3", ",");
+#endif
             assert(r);
     }
 

Objects/stringlib/localeutil.h

@@ -18,11 +18,13 @@
  * @append_zero_char: If non-zero, put a trailing zero at the end of
  *         of the resulting string, if and only if we modified the
  *         string.
+ * @grouping: see definition in localeconv().
+ * @thousands_sep: see definition in localeconv().
  *
- * Inserts thousand grouping characters (as defined in the current
+ * Inserts thousand grouping characters (as defined by grouping and
- *  locale) into the string between buffer and buffer+n_digits.  If
+ *  thousands_sep) into the string between buffer and buffer+n_digits.
- *  count is non-NULL, don't do any formatting, just count the number
+ *  If count is non-NULL, don't do any formatting, just count the
- *  of characters to insert.  This is used by the caller to
+ *  number of characters to insert.  This is used by the caller to
  *  appropriately resize the buffer, if needed.  If count is non-NULL,
  *  buffer can be NULL (it is not dereferenced at all in that case).
  *
@@ -38,11 +40,10 @@ _Py_InsertThousandsGrouping(STRINGLIB_CHAR *buffer,
                             Py_ssize_t n_digits,
                             Py_ssize_t buf_size,
                             Py_ssize_t *count,
-			    int append_zero_char)
+                            int append_zero_char,
+                            const char *grouping,
+                            const char *thousands_sep)
 {
-	struct lconv *locale_data = localeconv();
-	const char *grouping = locale_data->grouping;
-	const char *thousands_sep = locale_data->thousands_sep;
         Py_ssize_t thousands_sep_len = strlen(thousands_sep);
         STRINGLIB_CHAR *pend = NULL; /* current end of buffer */
         STRINGLIB_CHAR *pmax = NULL; /* max of buffer */
@@ -127,4 +128,38 @@ _Py_InsertThousandsGrouping(STRINGLIB_CHAR *buffer,
         }
         return 1;
 }
+
+/**
+ * _Py_InsertThousandsGroupingLocale:
+ * @buffer: A pointer to the start of a string.
+ * @n_buffer: The length of the string.
+ * @n_digits: The number of digits in the string, in which we want
+ *            to put the grouping chars.
+ * @buf_size: The maximum size of the buffer pointed to by buffer.
+ * @count: If non-NULL, points to a variable that will receive the
+ *         number of characters we need to insert (and no formatting
+ *         will actually occur).
+ * @append_zero_char: If non-zero, put a trailing zero at the end of
+ *         of the resulting string, if and only if we modified the
+ *         string.
+ *
+ * Reads thee current locale and calls _Py_InsertThousandsGrouping().
+ **/
+int
+_Py_InsertThousandsGroupingLocale(STRINGLIB_CHAR *buffer,
+                                  Py_ssize_t n_buffer,
+                                  Py_ssize_t n_digits,
+                                  Py_ssize_t buf_size,
+                                  Py_ssize_t *count,
+                                  int append_zero_char)
+{
+        struct lconv *locale_data = localeconv();
+        const char *grouping = locale_data->grouping;
+        const char *thousands_sep = locale_data->thousands_sep;
+
+        return _Py_InsertThousandsGrouping(buffer, n_buffer, n_digits,
+                                           buf_size, count,
+                                           append_zero_char, grouping,
+                                           thousands_sep);
+}
 #endif /* STRINGLIB_LOCALEUTIL_H */

Objects/stringlib/stringdefs.h

@@ -24,5 +24,6 @@
 #define STRINGLIB_CMP            memcmp
 #define STRINGLIB_TOSTR          PyObject_Str
 #define STRINGLIB_GROUPING       _PyBytes_InsertThousandsGrouping
+#define STRINGLIB_GROUPING_LOCALE _PyBytes_InsertThousandsGroupingLocale
 #define STRINGLIB_TOASCII        PyObject_Repr
 #endif /* !STRINGLIB_STRINGDEFS_H */

Objects/stringlib/unicodedefs.h

@@ -22,6 +22,7 @@
 #define STRINGLIB_RESIZE         PyUnicode_Resize
 #define STRINGLIB_CHECK          PyUnicode_Check
 #define STRINGLIB_GROUPING       _PyUnicode_InsertThousandsGrouping
+#define STRINGLIB_GROUPING_LOCALE _PyUnicode_InsertThousandsGroupingLocale
 
 #if PY_VERSION_HEX < 0x03000000
 #define STRINGLIB_TOSTR          PyObject_Unicode

Objects/unicodeobject.c

@@ -5635,6 +5635,7 @@ int PyUnicode_EncodeDecimal(Py_UNICODE *s,
 #include "stringlib/partition.h"
 
 #define _Py_InsertThousandsGrouping _PyUnicode_InsertThousandsGrouping
+#define _Py_InsertThousandsGroupingLocale _PyUnicode_InsertThousandsGroupingLocale
 #include "stringlib/localeutil.h"
 
 /* helper macro to fixup start/end slice values */

Python/pystrtod.c

@@ -368,7 +368,7 @@ add_thousands_grouping(char* buffer, size_t buf_size)
 	/* At this point, p points just past the right-most character we
 	   want to format.  We need to add the grouping string for the
 	   characters between buffer and p. */
-	return _PyBytes_InsertThousandsGrouping(buffer, len, p-buffer,
+	return _PyBytes_InsertThousandsGroupingLocale(buffer, len, p-buffer,
 						buf_size, NULL, 1);
 }