# String conversion and formatting

Functions for number conversion and formatted string output.

int PyOS_snprintf(char *str, size_t size, const char *format, ...)
  Del av Stabil ABI.

  Output not more than size bytes to str according to the format string format and the extra arguments. See the Unix man page snprintf(3).

int PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)
  Del av Stabil ABI.

  Output not more than size bytes to str according to the format string format and the variable argument list va. Unix man page vsnprintf(3).

`PyOS_snprintf()` and `PyOS_vsnprintf()` wrap the Standard C library functions `snprintf()` and `vsnprintf()`. Their purpose is to guarantee consistent behavior in corner cases, which the Standard C functions do not.

The wrappers ensure that `str[size-1]` is always `'\0'` upon return. They never write more than size bytes (including the trailing `'\0'`) into str. Both functions require that `str != NULL`, `size > 0`, `format != NULL` and `size < INT_MAX`. Note that this means there is no equivalent to the C99 `n = snprintf(NULL, 0, ...)` which would determine the necessary buffer size.

The return value (rv) for these functions should be interpreted as follows:

- When `0 <= rv < size`, the output conversion was successful and rv characters were written to str (excluding the trailing `'\0'` byte at `str[rv]`).

- When `rv >= size`, the output conversion was truncated and a buffer with `rv + 1` bytes would have been needed to succeed. `str[size-1]` is `'\0'` in this case.

- When `rv < 0`, the output conversion failed and `str[size-1]` is `'\0'` in this case too, but the rest of str is undefined. The exact cause of the error depends on the underlying platform.

The following functions provide locale-independent string to number conversions.

unsigned long PyOS_strtoul(const char *str, char **ptr, int base)
  Del av Stabil ABI.

  Convert the initial part of the string in `str` to an unsigned long value according to the given `base`, which must be between `2` and `36` inclusive, or be the special value `0`.

  Leading white space and case of characters are ignored. If `base` is zero it looks for a leading `0b`, `0o` or `0x` to tell which base. If these are absent it defaults to `10`. Base must be 0 or between 2 and 36 (inclusive). If `ptr` is non-`NULL` it will contain a pointer to the end of the scan.

  If the converted value falls out of range of corresponding return type, range error occurs (`errno` is set to `ERANGE`) and `ULONG_MAX` is returned. If no conversion can be performed, `0` is returned.

  See also the Unix man page strtoul(3).

  Added in version 3.2.

long PyOS_strtol(const char *str, char **ptr, int base)
  Del av Stabil ABI.

  Convert the initial part of the string in `str` to an long value according to the given `base`, which must be between `2` and `36` inclusive, or be the special value `0`.

  Same as `PyOS_strtoul()`, but return a long value instead and `LONG_MAX` on overflows.

  See also the Unix man page strtol(3).

  Added in version 3.2.

double PyOS_string_to_double(const char *s, char **endptr, PyObject *overflow_exception)
  Del av Stabil ABI.

  Convert a string `s` to a double, raising a Python exception on failure. The set of accepted strings corresponds to the set of strings accepted by Python’s `float()` constructor, except that `s` must not have leading or trailing whitespace. The conversion is independent of the current locale.

  If `endptr` is `NULL`, convert the whole string. Raise `ValueError` and return `-1.0` if the string is not a valid representation of a floating-point number.

  If endptr is not `NULL`, convert as much of the string as possible and set `*endptr` to point to the first unconverted character. If no initial segment of the string is the valid representation of a floating-point number, set `*endptr` to point to the beginning of the string, raise ValueError, and return `-1.0`.

  If `s` represents a value that is too large to store in a float (for example, `"1e500"` is such a string on many platforms) then if `overflow_exception` is `NULL` return `Py_INFINITY` (with an appropriate sign) and don’t set any exception. Otherwise, `overflow_exception` must point to a Python exception object; raise that exception and return `-1.0`. In both cases, set `*endptr` to point to the first character after the converted value.

  If any other error occurs during the conversion (for example an out-of-memory error), set the appropriate Python exception and return `-1.0`.

  Added in version 3.1.

char *PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype)
  Del av Stabil ABI.

  Convert a double val to a string using supplied format_code, precision, and flags.

  format_code must be one of `'e'`, `'E'`, `'f'`, `'F'`, `'g'`, `'G'` or `'r'`. For `'r'`, the supplied precision must be 0 and is ignored. The `'r'` format code specifies the standard `repr()` format.

  flags can be zero or more of the following values or-ed together:

  Py_DTSF_SIGN

    Always precede the returned string with a sign character, even if val is non-negative.

  Py_DTSF_ADD_DOT_0

    Ensure that the returned string will not look like an integer.

  Py_DTSF_ALT

    Apply ”alternate” formatting rules. See the documentation for the `PyOS_snprintf()` `'#'` specifier for details.

  Py_DTSF_NO_NEG_0

    Negative zero is converted to positive zero.

    Added in version 3.11.

  If ptype is non-`NULL`, then the value it points to will be set to one of the following constants depending on the type of val:

  *ptype | type of val
  --- | ---

  Py_DTST_FINITE

  finite number

  Py_DTST_INFINITE

  infinite number

  Py_DTST_NAN

  not a number

  The return value is a pointer to buffer with the converted string or `NULL` if the conversion failed. The caller is responsible for freeing the returned string by calling `PyMem_Free()`.

  Added in version 3.1.

int PyOS_mystricmp(const char *str1, const char *str2)
int PyOS_mystrnicmp(const char *str1, const char *str2, Py_ssize_t size)
  Del av Stabil ABI.

  Case insensitive comparison of strings. These functions work almost identically to `strcmp()` and `strncmp()` (respectively), except that they ignore the case of ASCII characters.

  Return `0` if the strings are equal, a negative value if str1 sorts lexicographically before str2, or a positive value if it sorts after.

  In the str1 or str2 arguments, a NUL byte marks the end of the string. For `PyOS_mystrnicmp()`, the size argument gives the maximum size of the string, as if NUL was present at the index given by size.

  These functions do not use the locale.

int PyOS_stricmp(const char *str1, const char *str2)
int PyOS_strnicmp(const char *str1, const char *str2, Py_ssize_t size)

  Case insensitive comparison of strings.

  On Windows, these are aliases of `stricmp()` and `strnicmp()`, respectively.

  On other platforms, they are aliases of `PyOS_mystricmp()` and `PyOS_mystrnicmp()`, respectively.

# Character classification and conversion

The following macros provide locale-independent (unlike the C standard library `ctype.h`) character classification and conversion. The argument must be a signed or unsigned char.

Py_ISALNUM(c)

  Return true if the character c is an alphanumeric character.

Py_ISALPHA(c)

  Return true if the character c is an alphabetic character (`a-z` and `A-Z`).

Py_ISDIGIT(c)

  Return true if the character c is a decimal digit (`0-9`).

Py_ISLOWER(c)

  Return true if the character c is a lowercase ASCII letter (`a-z`).

Py_ISUPPER(c)

  Return true if the character c is an uppercase ASCII letter (`A-Z`).

Py_ISSPACE(c)

  Return true if the character c is a whitespace character (space, tab, carriage return, newline, vertical tab, or form feed).

Py_ISXDIGIT(c)

  Return true if the character c is a hexadecimal digit (`0-9`, `a-f`, and `A-F`).

Py_TOLOWER(c)

  Return the lowercase equivalent of the character c.

Py_TOUPPER(c)

  Return the uppercase equivalent of the character c.