/*

string_format.h -- implementation of string.format().

It uses the Objects/stringlib conventions, so that it can be

compiled for both unicode and string objects.

*/

/* Defines for Python 2.6 compatability */

#if PY_VERSION_HEX < 0x03000000

#define PyLong_FromSsize_t _PyLong_FromSsize_t

#endif

/* Defines for more efficiently reallocating the string buffer */

#define INITIAL_SIZE_INCREMENT 100

#define SIZE_MULTIPLIER 2

#define MAX_SIZE_INCREMENT 3200

/************************************************************************/

/*********** Global data structures and forward declarations *********/

/************************************************************************/

/*

A SubString consists of the characters between two string or

unicode pointers.

*/

typedef struct {

STRINGLIB_CHAR *ptr;

STRINGLIB_CHAR *end;

} SubString;

/* forward declaration for recursion */

static PyObject *

build_string(SubString *input, PyObject *args, PyObject *kwargs,

int recursion_depth);

/************************************************************************/

/************************** Utility functions ************************/

/************************************************************************/

/* fill in a SubString from a pointer and length */

Py_LOCAL_INLINE(void)

SubString_init(SubString *str, STRINGLIB_CHAR *p, Py_ssize_t len)

{

str->ptr = p;

if (p == NULL)

str->end = NULL;

else

str->end = str->ptr + len;

}

/* return a new string. if str->ptr is NULL, return None */

Py_LOCAL_INLINE(PyObject *)

SubString_new_object(SubString *str)

{

if (str->ptr == NULL) {

Py_INCREF(Py_None);

return Py_None;

}

return STRINGLIB_NEW(str->ptr, str->end - str->ptr);

}

/* return a new string. if str->ptr is NULL, return None */

Py_LOCAL_INLINE(PyObject *)

SubString_new_object_or_empty(SubString *str)

{

if (str->ptr == NULL) {

return STRINGLIB_NEW(NULL, 0);

}

return STRINGLIB_NEW(str->ptr, str->end - str->ptr);

}

/************************************************************************/

/*********** Output string management functions ****************/

/************************************************************************/

typedef struct {

STRINGLIB_CHAR *ptr;

STRINGLIB_CHAR *end;

PyObject *obj;

Py_ssize_t size_increment;

} OutputString;

/* initialize an OutputString object, reserving size characters */

static int

output_initialize(OutputString *output, Py_ssize_t size)

{

output->obj = STRINGLIB_NEW(NULL, size);

if (output->obj == NULL)

return 0;

output->ptr = STRINGLIB_STR(output->obj);

output->end = STRINGLIB_LEN(output->obj) + output->ptr;

output->size_increment = INITIAL_SIZE_INCREMENT;

return 1;

}

/*

output_extend reallocates the output string buffer.

It returns a status: 0 for a failed reallocation,

1 for success.

*/

static int

output_extend(OutputString *output, Py_ssize_t count)

{

STRINGLIB_CHAR *startptr = STRINGLIB_STR(output->obj);

Py_ssize_t curlen = output->ptr - startptr;

Py_ssize_t maxlen = curlen + count + output->size_increment;

if (STRINGLIB_RESIZE(&output->obj, maxlen) < 0)

return 0;

startptr = STRINGLIB_STR(output->obj);

output->ptr = startptr + curlen;

output->end = startptr + maxlen;

if (output->size_increment < MAX_SIZE_INCREMENT)

output->size_increment *= SIZE_MULTIPLIER;

return 1;

}

/*

output_data dumps characters into our output string

buffer.

In some cases, it has to reallocate the string.

It returns a status: 0 for a failed reallocation,

1 for success.

*/

static int

output_data(OutputString *output, const STRINGLIB_CHAR *s, Py_ssize_t count)

{

if ((count > output->end - output->ptr) && !output_extend(output, count))

return 0;

memcpy(output->ptr, s, count * sizeof(STRINGLIB_CHAR));

output->ptr += count;

return 1;

}

/************************************************************************/

/*********** Format string parsing -- integers and identifiers *********/

/************************************************************************/

static Py_ssize_t

get_integer(const SubString *str)

{

Py_ssize_t accumulator = 0;

Py_ssize_t digitval;

Py_ssize_t oldaccumulator;

STRINGLIB_CHAR *p;

/* empty string is an error */

if (str->ptr >= str->end)

return -1;

for (p = str->ptr; p < str->end; p++) {

digitval = STRINGLIB_TODECIMAL(*p);

if (digitval < 0)

return -1;

/*

This trick was copied from old Unicode format code. It's cute,

but would really suck on an old machine with a slow divide

implementation. Fortunately, in the normal case we do not

expect too many digits.

*/

oldaccumulator = accumulator;

accumulator *= 10;

if ((accumulator+10)/10 != oldaccumulator+1) {

PyErr_Format(PyExc_ValueError,

"Too many decimal digits in format string");

return -1;

}

accumulator += digitval;

}

return accumulator;

}

/************************************************************************/

/******** Functions to get field objects and specification strings ******/

/************************************************************************/

/* do the equivalent of obj.name */

static PyObject *

getattr(PyObject *obj, SubString *name)

{

PyObject *newobj;

PyObject *str = SubString_new_object(name);

if (str == NULL)

return NULL;

newobj = PyObject_GetAttr(obj, str);

Py_DECREF(str);

return newobj;

}

/* do the equivalent of obj[idx], where obj is a sequence */

static PyObject *

getitem_sequence(PyObject *obj, Py_ssize_t idx)

{

return PySequence_GetItem(obj, idx);

}

/* do the equivalent of obj[idx], where obj is not a sequence */

static PyObject *

getitem_idx(PyObject *obj, Py_ssize_t idx)

{

PyObject *newobj;

PyObject *idx_obj = PyLong_FromSsize_t(idx);

if (idx_obj == NULL)

return NULL;

newobj = PyObject_GetItem(obj, idx_obj);

Py_DECREF(idx_obj);

return newobj;

}

/* do the equivalent of obj[name] */

static PyObject *

getitem_str(PyObject *obj, SubString *name)

{

PyObject *newobj;

PyObject *str = SubString_new_object(name);

if (str == NULL)

return NULL;

newobj = PyObject_GetItem(obj, str);

Py_DECREF(str);

return newobj;

}

typedef struct {

/* the entire string we're parsing. we assume that someone else

is managing its lifetime, and that it will exist for the

lifetime of the iterator. can be empty */

SubString str;

/* pointer to where we are inside field_name */

STRINGLIB_CHAR *ptr;

} FieldNameIterator;

static int

FieldNameIterator_init(FieldNameIterator *self, STRINGLIB_CHAR *ptr,

Py_ssize_t len)

{

SubString_init(&self->str, ptr, len);

self->ptr = self->str.ptr;

return 1;

}

static int

_FieldNameIterator_attr(FieldNameIterator *self, SubString *name)

{

STRINGLIB_CHAR c;

name->ptr = self->ptr;

/* return everything until '.' or '[' */

while (self->ptr < self->str.end) {

switch (c = *self->ptr++) {

case '[':

case '.':

/* backup so that we this character will be seen next time */

self->ptr--;

break;

default:

continue;

}

break;

}

/* end of string is okay */

name->end = self->ptr;

return 1;

}

static int

_FieldNameIterator_item(FieldNameIterator *self, SubString *name)

{

int bracket_seen = 0;

STRINGLIB_CHAR c;

name->ptr = self->ptr;

/* return everything until ']' */

while (self->ptr < self->str.end) {

switch (c = *self->ptr++) {

case ']':

bracket_seen = 1;

break;

default:

continue;

}

break;

}

/* make sure we ended with a ']' */

if (!bracket_seen) {

PyErr_SetString(PyExc_ValueError, "Missing ']' in format string");

return 0;

}

/* end of string is okay */

/* don't include the ']' */

name->end = self->ptr-1;

return 1;

}

/* returns 0 on error, 1 on non-error termination, and 2 if it returns a value */

static int

FieldNameIterator_next(FieldNameIterator *self, int *is_attribute,

Py_ssize_t *name_idx, SubString *name)

{

/* check at end of input */

if (self->ptr >= self->str.end)

return 1;

switch (*self->ptr++) {

case '.':

*is_attribute = 1;

if (_FieldNameIterator_attr(self, name) == 0)

return 0;

*name_idx = -1;

break;

case '[':

*is_attribute = 0;

if (_FieldNameIterator_item(self, name) == 0)

return 0;

*name_idx = get_integer(name);

break;

default:

/* Invalid character follows ']' */

PyErr_SetString(PyExc_ValueError, "Only '.' or '[' may "

"follow ']' in format field specifier");

return 0;

}

/* empty string is an error */

if (name->ptr == name->end) {

PyErr_SetString(PyExc_ValueError, "Empty attribute in format string");

return 0;

}

return 2;

}

/* input: field_name

output: 'first' points to the part before the first '[' or '.'

'first_idx' is -1 if 'first' is not an integer, otherwise

it's the value of first converted to an integer

'rest' is an iterator to return the rest

*/

static int

field_name_split(STRINGLIB_CHAR *ptr, Py_ssize_t len, SubString *first,

Py_ssize_t *first_idx, FieldNameIterator *rest)

{

STRINGLIB_CHAR c;

STRINGLIB_CHAR *p = ptr;

STRINGLIB_CHAR *end = ptr + len;

/* find the part up until the first '.' or '[' */

while (p < end) {

switch (c = *p++) {

case '[':

case '.':

/* backup so that we this character is available to the

"rest" iterator */

p--;

break;

default:

continue;

}

break;

}

/* set up the return values */

SubString_init(first, ptr, p - ptr);

FieldNameIterator_init(rest, p, end - p);

/* see if "first" is an integer, in which case it's used as an index */

*first_idx = get_integer(first);

/* zero length string is an error */

if (first->ptr >= first->end) {

PyErr_SetString(PyExc_ValueError, "empty field name");

goto error;

}

return 1;

error:

return 0;

}

/*

get_field_object returns the object inside {}, before the

format_spec. It handles getindex and getattr lookups and consumes

the entire input string.

*/

static PyObject *

get_field_object(SubString *input, PyObject *args, PyObject *kwargs)

{

PyObject *obj = NULL;

int ok;

int is_attribute;

SubString name;

SubString first;

Py_ssize_t index;

FieldNameIterator rest;

if (!field_name_split(input->ptr, input->end - input->ptr, &first,

&index, &rest)) {

goto error;

}

if (index == -1) {

/* look up in kwargs */

PyObject *key = SubString_new_object(&first);

if (key == NULL)

goto error;

if ((kwargs == NULL) || (obj = PyDict_GetItem(kwargs, key)) == NULL) {

PyErr_SetObject(PyExc_KeyError, key);

Py_DECREF(key);

goto error;

}

Py_DECREF(key);

Py_INCREF(obj);

}

else {

/* look up in args */

obj = PySequence_GetItem(args, index);

if (obj == NULL)

goto error;

}

/* iterate over the rest of the field_name */

while ((ok = FieldNameIterator_next(&rest, &is_attribute, &index,

&name)) == 2) {

PyObject *tmp;

if (is_attribute)

/* getattr lookup "." */

tmp = getattr(obj, &name);

else

/* getitem lookup "[]" */

if (index == -1)

tmp = getitem_str(obj, &name);

else

if (PySequence_Check(obj))

tmp = getitem_sequence(obj, index);

else

/* not a sequence */

tmp = getitem_idx(obj, index);

if (tmp == NULL)

goto error;

/* assign to obj */

Py_DECREF(obj);

obj = tmp;

}

/* end of iterator, this is the non-error case */

if (ok == 1)

return obj;

error:

Py_XDECREF(obj);

return NULL;

}

/************************************************************************/

/***************** Field rendering functions **************************/

/************************************************************************/

/*

render_field() is the main function in this section. It takes the

field object and field specification string generated by

get_field_and_spec, and renders the field into the output string.

render_field calls fieldobj.__format__(format_spec) method, and

appends to the output.

*/

static int

render_field(PyObject *fieldobj, SubString *format_spec, OutputString *output)

{

int ok = 0;

PyObject *result = NULL;

PyObject *format_spec_object = NULL;

PyObject *(*formatter)(PyObject *, STRINGLIB_CHAR *, Py_ssize_t) = NULL;

STRINGLIB_CHAR* format_spec_start = format_spec->ptr ?

format_spec->ptr : NULL;

Py_ssize_t format_spec_len = format_spec->ptr ?

format_spec->end - format_spec->ptr : 0;

/* If we know the type exactly, skip the lookup of __format__ and just

call the formatter directly. */

#if STRINGLIB_IS_UNICODE

if (PyUnicode_CheckExact(fieldobj))

formatter = _PyUnicode_FormatAdvanced;

/* Unfortunately, there's a problem with checking for int, long,

and float here. If we're being included as unicode, their

formatters expect string format_spec args. For now, just skip

this optimization for unicode. This could be fixed, but it's a

hassle. */

#else

if (PyString_CheckExact(fieldobj))

formatter = _PyBytes_FormatAdvanced;

else if (PyInt_CheckExact(fieldobj))

formatter =_PyInt_FormatAdvanced;

else if (PyLong_CheckExact(fieldobj))

formatter =_PyLong_FormatAdvanced;

else if (PyFloat_CheckExact(fieldobj))

formatter = _PyFloat_FormatAdvanced;

#endif

if (formatter) {

/* we know exactly which formatter will be called when __format__ is

looked up, so call it directly, instead. */

result = formatter(fieldobj, format_spec_start, format_spec_len);

}

else {

/* We need to create an object out of the pointers we have, because

__format__ takes a string/unicode object for format_spec. */

format_spec_object = STRINGLIB_NEW(format_spec_start,

format_spec_len);

if (format_spec_object == NULL)

goto done;

result = PyObject_Format(fieldobj, format_spec_object);

}

if (result == NULL)

goto done;

#if PY_VERSION_HEX >= 0x03000000

assert(PyUnicode_Check(result));

#else

assert(PyString_Check(result) || PyUnicode_Check(result));

/* Convert result to our type. We could be str, and result could

be unicode */

{

PyObject *tmp = STRINGLIB_TOSTR(result);

if (tmp == NULL)

goto done;

Py_DECREF(result);

result = tmp;

}

#endif

ok = output_data(output,

STRINGLIB_STR(result), STRINGLIB_LEN(result));

done:

Py_XDECREF(format_spec_object);

Py_XDECREF(result);

return ok;

}

static int

parse_field(SubString *str, SubString *field_name, SubString *format_spec,

STRINGLIB_CHAR *conversion)

{

STRINGLIB_CHAR c = 0;

/* initialize these, as they may be empty */

*conversion = '\0';

SubString_init(format_spec, NULL, 0);

/* search for the field name. it's terminated by the end of the

string, or a ':' or '!' */

field_name->ptr = str->ptr;

while (str->ptr < str->end) {

switch (c = *(str->ptr++)) {

case ':':

case '!':

break;

default:

continue;

}

break;

}

if (c == '!' || c == ':') {

/* we have a format specifier and/or a conversion */

/* don't include the last character */

field_name->end = str->ptr-1;

/* the format specifier is the rest of the string */

format_spec->ptr = str->ptr;

format_spec->end = str->end;

/* see if there's a conversion specifier */

if (c == '!') {

/* there must be another character present */

if (format_spec->ptr >= format_spec->end) {

PyErr_SetString(PyExc_ValueError,

"end of format while looking for conversion "

"specifier");

return 0;

}

*conversion = *(format_spec->ptr++);

/* if there is another character, it must be a colon */

if (format_spec->ptr < format_spec->end) {

c = *(format_spec->ptr++);

if (c != ':') {

PyErr_SetString(PyExc_ValueError,

"expected ':' after format specifier");

return 0;

}

}

}

return 1;

}

else {

/* end of string, there's no format_spec or conversion */

field_name->end = str->ptr;

return 1;

}

}

/************************************************************************/

/******* Output string allocation and escape-to-markup processing ******/

/************************************************************************/

/* MarkupIterator breaks the string into pieces of either literal

text, or things inside {} that need to be marked up. it is

designed to make it easy to wrap a Python iterator around it, for

use with the Formatter class */

typedef struct {

SubString str;

} MarkupIterator;

static int

MarkupIterator_init(MarkupIterator *self, STRINGLIB_CHAR *ptr, Py_ssize_t len)

{

SubString_init(&self->str, ptr, len);

return 1;

}

/* returns 0 on error, 1 on non-error termination, and 2 if it got a

string (or something to be expanded) */

static int

MarkupIterator_next(MarkupIterator *self, SubString *literal,

SubString *field_name, SubString *format_spec,

STRINGLIB_CHAR *conversion,

int *format_spec_needs_expanding)

{

int at_end;

STRINGLIB_CHAR c = 0;

STRINGLIB_CHAR *start;

int count;

Py_ssize_t len;

int markup_follows = 0;

/* initialize all of the output variables */

SubString_init(literal, NULL, 0);

SubString_init(field_name, NULL, 0);

SubString_init(format_spec, NULL, 0);

*conversion = '\0';

*format_spec_needs_expanding = 0;

/* No more input, end of iterator. This is the normal exit

path. */

if (self->str.ptr >= self->str.end)

return 1;

start = self->str.ptr;

/* First read any literal text. Read until the end of string, an

escaped '{' or '}', or an unescaped '{'. In order to never

allocate memory and so I can just pass pointers around, if

there's an escaped '{' or '}' then we'll return the literal

including the brace, but no format object. The next time

through, we'll return the rest of the literal, skipping past

the second consecutive brace. */

while (self->str.ptr < self->str.end) {

switch (c = *(self->str.ptr++)) {

case '{':

case '}':

markup_follows = 1;

break;

default:

continue;

}

break;

}

at_end = self->str.ptr >= self->str.end;

len = self->str.ptr - start;

if ((c == '}') && (at_end || (c != *self->str.ptr))) {

PyErr_SetString(PyExc_ValueError, "Single '}' encountered "

"in format string");

return 0;

}

if (at_end && c == '{') {

PyErr_SetString(PyExc_ValueError, "Single '{' encountered "

"in format string");

return 0;

}

if (!at_end) {

if (c == *self->str.ptr) {

/* escaped } or {, skip it in the input. there is no

markup object following us, just this literal text */

self->str.ptr++;

markup_follows = 0;

}

else

len--;

}

/* record the literal text */

literal->ptr = start;

literal->end = start + len;

if (!markup_follows)

return 2;

/* this is markup, find the end of the string by counting nested

braces. note that this prohibits escaped braces, so that

format_specs cannot have braces in them. */

count = 1;

start = self->str.ptr;

/* we know we can't have a zero length string, so don't worry

about that case */

while (self->str.ptr < self->str.end) {

switch (c = *(self->str.ptr++)) {

case '{':

/* the format spec needs to be recursively expanded.

this is an optimization, and not strictly needed */

*format_spec_needs_expanding = 1;

count++;

break;

case '}':

count--;

if (count <= 0) {

/* we're done. parse and get out */

SubString s;

SubString_init(&s, start, self->str.ptr - 1 - start);

if (parse_field(&s, field_name, format_spec, conversion) == 0)

return 0;

/* a zero length field_name is an error */

if (field_name->ptr == field_name->end) {

PyErr_SetString(PyExc_ValueError, "zero length field name "

"in format");

return 0;

}

/* success */

return 2;

}

break;

}

}

/* end of string while searching for matching '}' */

PyErr_SetString(PyExc_ValueError, "unmatched '{' in format");

return 0;

}

/* do the !r or !s conversion on obj */

static PyObject *

do_conversion(PyObject *obj, STRINGLIB_CHAR conversion)

{

/* XXX in pre-3.0, do we need to convert this to unicode, since it

might have returned a string? */

switch (conversion) {

case 'r':

return PyObject_Repr(obj);

case 's':

return STRINGLIB_TOSTR(obj);

default:

if (conversion > 32 && conversion < 127) {

/* It's the ASCII subrange; casting to char is safe

(assuming the execution character set is an ASCII

superset). */

PyErr_Format(PyExc_ValueError,

"Unknown conversion specifier %c",

(char)conversion);

} else

PyErr_Format(PyExc_ValueError,

"Unknown conversion specifier \\x%x",

(unsigned int)conversion);

return NULL;

}

}

/* given:

{field_name!conversion:format_spec}

compute the result and write it to output.

format_spec_needs_expanding is an optimization. if it's false,

just output the string directly, otherwise recursively expand the

format_spec string. */

static int

output_markup(SubString *field_name, SubString *format_spec,

int format_spec_needs_expanding, STRINGLIB_CHAR conversion,

OutputString *output, PyObject *args, PyObject *kwargs,

int recursion_depth)

{

PyObject *tmp = NULL;

PyObject *fieldobj = NULL;

SubString expanded_format_spec;

SubString *actual_format_spec;

int result = 0;

/* convert field_name to an object */

fieldobj = get_field_object(field_name, args, kwargs);

if (fieldobj == NULL)

goto done;

if (conversion != '\0') {

tmp = do_conversion(fieldobj, conversion);

if (tmp == NULL)

goto done;

/* do the assignment, transferring ownership: fieldobj = tmp */

Py_DECREF(fieldobj);

fieldobj = tmp;

tmp = NULL;

}

/* if needed, recurively compute the format_spec */

if (format_spec_needs_expanding) {

tmp = build_string(format_spec, args, kwargs, recursion_depth-1);

if (tmp == NULL)

goto done;

/* note that in the case we're expanding the format string,

tmp must be kept around until after the call to

render_field. */

SubString_init(&expanded_format_spec,

STRINGLIB_STR(tmp), STRINGLIB_LEN(tmp));

actual_format_spec = &expanded_format_spec;

}

else

actual_format_spec = format_spec;

if (render_field(fieldobj, actual_format_spec, output) == 0)

goto done;

result = 1;

done:

Py_XDECREF(fieldobj);

Py_XDECREF(tmp);

return result;

}

/*

do_markup is the top-level loop for the format() method. It

searches through the format string for escapes to markup codes, and

calls other functions to move non-markup text to the output,

and to perform the markup to the output.

*/

static int

do_markup(SubString *input, PyObject *args, PyObject *kwargs,

OutputString *output, int recursion_depth)

{

MarkupIterator iter;

int format_spec_needs_expanding;

int result;

SubString literal;

SubString field_name;

SubString format_spec;

STRINGLIB_CHAR conversion;

MarkupIterator_init(&iter, input->ptr, input->end - input->ptr);

while ((result = MarkupIterator_next(&iter, &literal, &field_name,

&format_spec, &conversion,

&format_spec_needs_expanding)) == 2) {

if (!output_data(output, literal.ptr, literal.end - literal.ptr))

return 0;

if (field_name.ptr != field_name.end)

if (!output_markup(&field_name, &format_spec,

format_spec_needs_expanding, conversion, output,

args, kwargs, recursion_depth))

return 0;

}

return result;

}

/*

build_string allocates the output string and then

calls do_markup to do the heavy lifting.

*/

static PyObject *

build_string(SubString *input, PyObject *args, PyObject *kwargs,

int recursion_depth)

{

OutputString output;

PyObject *result = NULL;

Py_ssize_t count;

output.obj = NULL; /* needed so cleanup code always works */

/* check the recursion level */

if (recursion_depth <= 0) {

PyErr_SetString(PyExc_ValueError,

"Max string recursion exceeded");

goto done;

}

/* initial size is the length of the format string, plus the size

increment. seems like a reasonable default */

if (!output_initialize(&output,

input->end - input->ptr +

INITIAL_SIZE_INCREMENT))

goto done;

if (!do_markup(input, args, kwargs, &output, recursion_depth)) {

goto done;

}

count = output.ptr - STRINGLIB_STR(output.obj);

if (STRINGLIB_RESIZE(&output.obj, count) < 0) {

goto done;

}

/* transfer ownership to result */

result = output.obj;

output.obj = NULL;

done:

Py_XDECREF(output.obj);

return result;

}

/************************************************************************/

/*********** main routine ***********************************************/

/************************************************************************/

/* this is the main entry point */

static PyObject *

do_string_format(PyObject *self, PyObject *args, PyObject *kwargs)

{

SubString input;

/* PEP 3101 says only 2 levels, so that

"{0:{1}}".format('abc', 's') # works

"{0:{1:{2}}}".format('abc', 's', '') # fails

*/

int recursion_depth = 2;

SubString_init(&input, STRINGLIB_STR(self), STRINGLIB_LEN(self));

return build_string(&input, args, kwargs, recursion_depth);

}

/************************************************************************/

/*********** formatteriterator ******************************************/

/************************************************************************/

/* This is used to implement string.Formatter.vparse(). It exists so

Formatter can share code with the built in unicode.format() method.

It's really just a wrapper around MarkupIterator that is callable

from Python. */

typedef struct {

PyObject_HEAD

STRINGLIB_OBJECT *str;

MarkupIterator it_markup;

} formatteriterobject;

static void

formatteriter_dealloc(formatteriterobject *it)

{

Py_XDECREF(it->str);

PyObject_FREE(it);

}

/* returns a tuple:

(literal, field_name, format_spec, conversion)

literal is any literal text to output. might be zero length

field_name is the string before the ':'. might be None

format_spec is the string after the ':'. mibht be None

conversion is either None, or the string after the '!'

*/

static PyObject *

formatteriter_next(formatteriterobject *it)

{

SubString literal;

SubString field_name;

SubString format_spec;

STRINGLIB_CHAR conversion;