.. highlightlang:: c

.. _string-conversion:

String conversion and formatting

Functions for number conversion and formatted string output.

.. cfunction:: int PyOS_snprintf(char *str, size_t size, const char *format, ...)

Output not more than *size* bytes to *str* according to the format string

*format* and the extra arguments. See the Unix man page :manpage:`snprintf(2)`.

.. cfunction:: int PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)

Output not more than *size* bytes to *str* according to the format string

*format* and the variable argument list *va*. Unix man page

:manpage:`vsnprintf(2)`.

:cfunc:`PyOS_snprintf` and :cfunc:`PyOS_vsnprintf` wrap the Standard C library

functions :cfunc:`snprintf` and :cfunc:`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`` and ``format !=

NULL``.

If the platform doesn't have :cfunc:`vsnprintf` and the buffer size needed to

avoid truncation exceeds *size* by more than 512 bytes, Python aborts with a

*Py_FatalError*.

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``, "something bad happened." *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.

.. cfunction:: double PyOS_ascii_strtod(const char *nptr, char **endptr)

Convert a string to a :ctype:`double`. This function behaves like the Standard C

function :cfunc:`strtod` does in the C locale. It does this without changing the

current locale, since that would not be thread-safe.

:cfunc:`PyOS_ascii_strtod` should typically be used for reading configuration

files or other non-user input that should be locale independent.

.. versionadded:: 2.4

See the Unix man page :manpage:`strtod(2)` for details.

.. cfunction:: char * PyOS_ascii_formatd(char *buffer, size_t buf_len, const char *format, double d)

Convert a :ctype:`double` to a string using the ``'.'`` as the decimal

separator. *format* is a :cfunc:`printf`\ -style format string specifying the

number format. Allowed conversion characters are ``'e'``, ``'E'``, ``'f'``,

``'F'``, ``'g'`` and ``'G'``.

The return value is a pointer to *buffer* with the converted string or NULL if

the conversion failed.

.. versionadded:: 2.4

.. cfunction:: double PyOS_ascii_atof(const char *nptr)

Convert a string to a :ctype:`double` in a locale-independent way.

.. versionadded:: 2.4

See the Unix man page :manpage:`atof(2)` for details.

.. cfunction:: char * PyOS_stricmp(char *s1, char *s2)

Case insensitive comparsion of strings. The functions works almost

identical to :cfunc:`strcmp` except that it ignores the case.

.. versionadded:: 2.6

.. cfunction:: char * PyOS_strnicmp(char *s1, char *s2, Py_ssize_t size)

Case insensitive comparsion of strings. The functions works almost

identical to :cfunc:`strncmp` except that it ignores the case.

.. versionadded:: 2.6

.. highlightlang:: c

.. _importing:

Importing Modules

.. cfunction:: PyObject* PyImport_ImportModule(const char *name)

.. index::

single: package variable; __all__

single: __all__ (package variable)

single: modules (in module sys)

This is a simplified interface to :cfunc:`PyImport_ImportModuleEx` below,

leaving the *globals* and *locals* arguments set to *NULL* and *level* set

to 0. When the *name*

argument contains a dot (when it specifies a submodule of a package), the

*fromlist* argument is set to the list ``['*']`` so that the return value is the

named module rather than the top-level package containing it as would otherwise

be the case. (Unfortunately, this has an additional side effect when *name* in

fact specifies a subpackage instead of a submodule: the submodules specified in

the package's ``__all__`` variable are loaded.) Return a new reference to the

imported module, or *NULL* with an exception set on failure. Before Python 2.4,

the module may still be created in the failure case --- examine ``sys.modules``

to find out. Starting with Python 2.4, a failing import of a module no longer

leaves the module in ``sys.modules``.

.. versionchanged:: 2.4

failing imports remove incomplete module objects.

.. versionchanged:: 2.6

always use absolute imports

.. cfunction:: PyObject* PyImport_ImportModuleNoBlock(const char *name)

This version of :cfunc:`PyImport_ImportModule` does not block. It's intended

to be used in C functions that import other modules to execute a function.

The import may block if another thread holds the import lock. The function

:cfunc:`PyImport_ImportModuleNoBlock` never blocks. It first tries to fetch

the module from sys.modules and falls back to :cfunc:`PyImport_ImportModule`

unless the lock is held, in which case the function will raise an

:exc:`ImportError`.

.. versionadded:: 2.6

.. cfunction:: PyObject* PyImport_ImportModuleEx(char *name, PyObject *globals, PyObject *locals, PyObject *fromlist)

.. index:: builtin: __import__

Import a module. This is best described by referring to the built-in Python

function :func:`__import__`, as the standard :func:`__import__` function calls

this function directly.

The return value is a new reference to the imported module or top-level package,

or *NULL* with an exception set on failure (before Python 2.4, the module may

still be created in this case). Like for :func:`__import__`, the return value

when a submodule of a package was requested is normally the top-level package,

unless a non-empty *fromlist* was given.

.. versionchanged:: 2.4

failing imports remove incomplete module objects.

.. versionchanged:: 2.6

The function is an alias for :cfunc:`PyImport_ImportModuleLevel` with

-1 as level, meaning relative import.

.. cfunction:: PyObject* PyImport_ImportModuleLevel(char *name, PyObject *globals, PyObject *locals, PyObject *fromlist, int level)

Import a module. This is best described by referring to the built-in Python

function :func:`__import__`, as the standard :func:`__import__` function calls

this function directly.

The return value is a new reference to the imported module or top-level package,

or *NULL* with an exception set on failure. Like for :func:`__import__`,

the return value when a submodule of a package was requested is normally the

top-level package, unless a non-empty *fromlist* was given.

.. versionadded:: 2.5

.. cfunction:: PyObject* PyImport_Import(PyObject *name)

.. index::

module: rexec

module: ihooks

This is a higher-level interface that calls the current "import hook function".

It invokes the :func:`__import__` function from the ``__builtins__`` of the

current globals. This means that the import is done using whatever import hooks

are installed in the current environment, e.g. by :mod:`rexec` or :mod:`ihooks`.

.. versionchanged:: 2.6

always use absolute imports

.. cfunction:: PyObject* PyImport_ReloadModule(PyObject *m)

.. index:: builtin: reload

Reload a module. This is best described by referring to the built-in Python

function :func:`reload`, as the standard :func:`reload` function calls this

function directly. Return a new reference to the reloaded module, or *NULL*

with an exception set on failure (the module still exists in this case).

.. cfunction:: PyObject* PyImport_AddModule(const char *name)

Return the module object corresponding to a module name. The *name* argument

may be of the form ``package.module``. First check the modules dictionary if

there's one there, and if not, create a new one and insert it in the modules

dictionary. Return *NULL* with an exception set on failure.

.. note::

This function does not load or import the module; if the module wasn't already

loaded, you will get an empty module object. Use :cfunc:`PyImport_ImportModule`

or one of its variants to import a module. Package structures implied by a

dotted name for *name* are not created if not already present.

.. cfunction:: PyObject* PyImport_ExecCodeModule(char *name, PyObject *co)

.. index:: builtin: compile

Given a module name (possibly of the form ``package.module``) and a code object

read from a Python bytecode file or obtained from the built-in function

:func:`compile`, load the module. Return a new reference to the module object,

or *NULL* with an exception set if an error occurred. Before Python 2.4, the

module could still be created in error cases. Starting with Python 2.4, *name*

is removed from :attr:`sys.modules` in error cases, and even if *name* was already

in :attr:`sys.modules` on entry to :cfunc:`PyImport_ExecCodeModule`. Leaving

incompletely initialized modules in :attr:`sys.modules` is dangerous, as imports of

such modules have no way to know that the module object is an unknown (and

probably damaged with respect to the module author's intents) state.

This function will reload the module if it was already imported. See

:cfunc:`PyImport_ReloadModule` for the intended way to reload a module.

If *name* points to a dotted name of the form ``package.module``, any package

structures not already created will still not be created.

.. versionchanged:: 2.4

*name* is removed from :attr:`sys.modules` in error cases.

.. cfunction:: long PyImport_GetMagicNumber()

Return the magic number for Python bytecode files (a.k.a. :file:`.pyc` and

:file:`.pyo` files). The magic number should be present in the first four bytes

of the bytecode file, in little-endian byte order.

.. cfunction:: PyObject* PyImport_GetModuleDict()

Return the dictionary used for the module administration (a.k.a.

``sys.modules``). Note that this is a per-interpreter variable.

.. cfunction:: void _PyImport_Init()

Initialize the import mechanism. For internal use only.

.. cfunction:: void PyImport_Cleanup()

Empty the module table. For internal use only.

.. cfunction:: void _PyImport_Fini()

Finalize the import mechanism. For internal use only.

.. cfunction:: PyObject* _PyImport_FindExtension(char *, char *)

For internal use only.

.. cfunction:: PyObject* _PyImport_FixupExtension(char *, char *)

For internal use only.

.. cfunction:: int PyImport_ImportFrozenModule(char *name)

Load a frozen module named *name*. Return ``1`` for success, ``0`` if the

module is not found, and ``-1`` with an exception set if the initialization

failed. To access the imported module on a successful load, use

:cfunc:`PyImport_ImportModule`. (Note the misnomer --- this function would

reload the module if it was already imported.)

.. ctype:: struct _frozen

.. index:: single: freeze utility

This is the structure type definition for frozen module descriptors, as

generated by the :program:`freeze` utility (see :file:`Tools/freeze/` in the

Python source distribution). Its definition, found in :file:`Include/import.h`,

is::

.. cvar:: struct _frozen* PyImport_FrozenModules

This pointer is initialized to point to an array of :ctype:`struct _frozen`

records, terminated by one whose members are all *NULL* or zero. When a frozen

module is imported, it is searched in this table. Third-party code could play

tricks with this to provide a dynamically created collection of frozen modules.

.. cfunction:: int PyImport_AppendInittab(char *name, void (*initfunc)(void))

Add a single module to the existing table of built-in modules. This is a

convenience wrapper around :cfunc:`PyImport_ExtendInittab`, returning ``-1`` if

the table could not be extended. The new module can be imported by the name

*name*, and uses the function *initfunc* as the initialization function called

on the first attempted import. This should be called before

:cfunc:`Py_Initialize`.

.. ctype:: struct _inittab

Structure describing a single entry in the list of built-in modules. Each of

these structures gives the name and initialization function for a module built

into the interpreter. Programs which embed Python may use an array of these

structures in conjunction with :cfunc:`PyImport_ExtendInittab` to provide

additional built-in modules. The structure is defined in

:file:`Include/import.h` as::

.. cfunction:: int PyImport_ExtendInittab(struct _inittab *newtab)

Add a collection of modules to the table of built-in modules. The *newtab*

array must end with a sentinel entry which contains *NULL* for the :attr:`name`

field; failure to provide the sentinel value can result in a memory fault.

Returns ``0`` on success or ``-1`` if insufficient memory could be allocated to

extend the internal table. In the event of failure, no modules are added to the

internal table. This should be called before :cfunc:`Py_Initialize`.