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:mod:`msvcrt` --- Useful routines from the MS VC++ runtime
==========================================================
.. module:: msvcrt
:platform: Windows
:synopsis: Miscellaneous useful routines from the MS VC++ runtime.
.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>
--------------
These functions provide access to some useful capabilities on Windows platforms.
Some higher-level modules use these functions to build the Windows
implementations of their services. For example, the :mod:`getpass` module uses
this in the implementation of the :func:`getpass` function.
Further documentation on these functions can be found in the Platform API
documentation.
The module implements both the normal and wide char variants of the console I/O
api. The normal API deals only with ASCII characters and is of limited use
for internationalized applications. The wide char API should be used where
ever possible.
.. versionchanged:: 3.3
Operations in this module now raise :exc:`OSError` where :exc:`IOError`
was raised.
.. _msvcrt-files:
File Operations
---------------
.. function:: locking(fd, mode, nbytes)
Lock part of a file based on file descriptor *fd* from the C runtime. Raises
:exc:`OSError` on failure. The locked region of the file extends from the
current file position for *nbytes* bytes, and may continue beyond the end of the
file. *mode* must be one of the :const:`!LK_\*` constants listed below. Multiple
regions in a file may be locked at the same time, but may not overlap. Adjacent
regions are not merged; they must be unlocked individually.
.. audit-event:: msvcrt.locking fd,mode,nbytes msvcrt.locking
.. data:: LK_LOCK
LK_RLCK
Locks the specified bytes. If the bytes cannot be locked, the program
immediately tries again after 1 second. If, after 10 attempts, the bytes cannot
be locked, :exc:`OSError` is raised.
.. data:: LK_NBLCK
LK_NBRLCK
Locks the specified bytes. If the bytes cannot be locked, :exc:`OSError` is
raised.
.. data:: LK_UNLCK
Unlocks the specified bytes, which must have been previously locked.
.. function:: setmode(fd, flags)
Set the line-end translation mode for the file descriptor *fd*. To set it to
text mode, *flags* should be :const:`os.O_TEXT`; for binary, it should be
:const:`os.O_BINARY`.
.. function:: open_osfhandle(handle, flags)
Create a C runtime file descriptor from the file handle *handle*. The *flags*
parameter should be a bitwise OR of :const:`os.O_APPEND`,
:const:`os.O_RDONLY`, :const:`os.O_TEXT` and :const:`os.O_NOINHERIT`.
The returned file descriptor may be used as a parameter
to :func:`os.fdopen` to create a file object.
The file descriptor is inheritable by default. Pass :const:`os.O_NOINHERIT`
flag to make it non inheritable.
.. audit-event:: msvcrt.open_osfhandle handle,flags msvcrt.open_osfhandle
.. function:: get_osfhandle(fd)
Return the file handle for the file descriptor *fd*. Raises :exc:`OSError` if
*fd* is not recognized.
.. audit-event:: msvcrt.get_osfhandle fd msvcrt.get_osfhandle
.. _msvcrt-console:
Console I/O
-----------
.. function:: kbhit()
Returns a nonzero value if a keypress is waiting to be read. Otherwise,
return 0.
.. function:: getch()
Read a keypress and return the resulting character as a byte string.
Nothing is echoed to the console. This call will block if a keypress
is not already available, but will not wait for :kbd:`Enter` to be
pressed. If the pressed key was a special function key, this will
return ``'\000'`` or ``'\xe0'``; the next call will return the keycode.
The :kbd:`Control-C` keypress cannot be read with this function.
.. function:: getwch()
Wide char variant of :func:`getch`, returning a Unicode value.
.. function:: getche()
Similar to :func:`getch`, but the keypress will be echoed if it represents a
printable character.
.. function:: getwche()
Wide char variant of :func:`getche`, returning a Unicode value.
.. function:: putch(char)
Print the byte string *char* to the console without buffering.
.. function:: putwch(unicode_char)
Wide char variant of :func:`putch`, accepting a Unicode value.
.. function:: ungetch(char)
Cause the byte string *char* to be "pushed back" into the console buffer;
it will be the next character read by :func:`getch` or :func:`getche`.
.. function:: ungetwch(unicode_char)
Wide char variant of :func:`ungetch`, accepting a Unicode value.
.. _msvcrt-other:
Other Functions
---------------
.. function:: heapmin()
Force the :c:func:`malloc` heap to clean itself up and return unused blocks to
the operating system. On failure, this raises :exc:`OSError`.
.. function:: set_error_mode(mode)
Changes the location where the C runtime writes an error message for an error
that might end the program. *mode* must be one of the :const:`!OUT_\*`
constants listed below or :const:`REPORT_ERRMODE`. Returns the old setting
or -1 if an error occurs. Only available in
:ref:`debug build of Python <debug-build>`.
.. data:: OUT_TO_DEFAULT
Error sink is determined by the app's type. Only available in
:ref:`debug build of Python <debug-build>`.
.. data:: OUT_TO_STDERR
Error sink is a standard error. Only available in
:ref:`debug build of Python <debug-build>`.
.. data:: OUT_TO_MSGBOX
Error sink is a message box. Only available in
:ref:`debug build of Python <debug-build>`.
.. data:: REPORT_ERRMODE
Report the current error mode value. Only available in
:ref:`debug build of Python <debug-build>`.
.. function:: CrtSetReportMode(type, mode)
Specifies the destination or destinations for a specific report type
generated by :c:func:`!_CrtDbgReport` in the MS VC++ runtime. *type* must be
one of the :const:`!CRT_\*` constants listed below. *mode* must be one of the
:const:`!CRTDBG_\*` constants listed below. Only available in
:ref:`debug build of Python <debug-build>`.
.. function:: CrtSetReportFile(type, file)
After you use :func:`CrtSetReportMode` to specify :const:`CRTDBG_MODE_FILE`,
you can specify the file handle to receive the message text. *type* must be
one of the :const:`!CRT_\*` constants listed below. *file* shuld be the file
handle your want specified. Only available in
:ref:`debug build of Python <debug-build>`.
.. data:: CRT_WARN
Warnings, messages, and information that doesn't need immediate attention.
.. data:: CRT_ERROR
Errors, unrecoverable problems, and issues that require immediate attention.
.. data:: CRT_ASSERT
Assertion failures.
.. data:: CRTDBG_MODE_DEBUG
Writes the message to the debugger's output window.
.. data:: CRTDBG_MODE_FILE
Writes the message to a user-supplied file handle. :func:`CrtSetReportFile`
should be called to define the specific file or stream to use as
the destination.
.. data:: CRTDBG_MODE_WNDW
Creates a message box to display the message along with the ``Abort``,
``Retry``, and ``Ignore`` buttons.
.. data:: CRTDBG_REPORT_MODE
Returns current *mode* for the specified *type*.
.. data:: CRT_ASSEMBLY_VERSION
The CRT Assembly version, from the :file:`crtassem.h` header file.
.. data:: VC_ASSEMBLY_PUBLICKEYTOKEN
The VC Assembly public key token, from the :file:`crtassem.h` header file.
.. data:: LIBRARIES_ASSEMBLY_NAME_PREFIX
The Libraries Assembly name prefix, from the :file:`crtassem.h` header file.
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