# `msvcrt` — Useful routines from the MS VC++ runtime

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 `getpass` module uses this in the implementation of the `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.

Changed in version 3.3: Operations in this module now raise `OSError` where `IOError` was raised.

## File Operations

msvcrt.locking(fd, mode, nbytes)

  Lock part of a file based on file descriptor fd from the C runtime. Raises `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 `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.

  Raises an auditing event `msvcrt.locking` with arguments `fd`, `mode`, `nbytes`.

msvcrt.LK_LOCK
msvcrt.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, `OSError` is raised.

msvcrt.LK_NBLCK
msvcrt.LK_NBRLCK

  Locks the specified bytes. If the bytes cannot be locked, `OSError` is raised.

msvcrt.LK_UNLCK

  Unlocks the specified bytes, which must have been previously locked.

msvcrt.setmode(fd, flags)

  Set the line-end translation mode for the file descriptor fd. To set it to text mode, flags should be `os.O_TEXT`; for binary, it should be `os.O_BINARY`.

msvcrt.open_osfhandle(handle, flags)

  Create a C runtime file descriptor from the file handle handle. The flags parameter should be a bitwise OR of `os.O_APPEND`, `os.O_RDONLY`, `os.O_TEXT` and `os.O_NOINHERIT`. The returned file descriptor may be used as a parameter to `os.fdopen()` to create a file object.

  The file descriptor is inheritable by default. Pass `os.O_NOINHERIT` flag to make it non inheritable.

  Raises an auditing event `msvcrt.open_osfhandle` with arguments `handle`, `flags`.

msvcrt.get_osfhandle(fd)

  Return the file handle for the file descriptor fd. Raises `OSError` if fd is not recognized.

  Raises an auditing event `msvcrt.get_osfhandle` with argument `fd`.

## Console I/O

msvcrt.kbhit()

  Returns a nonzero value if a keypress is waiting to be read. Otherwise, return 0.

msvcrt.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 `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 `Control`-`C` keypress cannot be read with this function.

msvcrt.getwch()

  Wide char variant of `getch()`, returning a Unicode value.

msvcrt.getche()

  Similar to `getch()`, but the keypress will be echoed if it represents a printable character.

msvcrt.getwche()

  Wide char variant of `getche()`, returning a Unicode value.

msvcrt.putch(char)

  Print the byte string char to the console without buffering.

msvcrt.putwch(unicode_char)

  Wide char variant of `putch()`, accepting a Unicode value.

msvcrt.ungetch(char)

  Cause the byte string char to be “pushed back” into the console buffer; it will be the next character read by `getch()` or `getche()`.

msvcrt.ungetwch(unicode_char)

  Wide char variant of `ungetch()`, accepting a Unicode value.

## Other Functions

msvcrt.heapmin()

  Force the `malloc()` heap to clean itself up and return unused blocks to the operating system. On failure, this raises `OSError`.

msvcrt.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 `OUT_*` constants listed below or `REPORT_ERRMODE`. Returns the old setting or -1 if an error occurs. Only available in debug build of Python.

msvcrt.OUT_TO_DEFAULT

  Error sink is determined by the app’s type. Only available in debug build of Python.

msvcrt.OUT_TO_STDERR

  Error sink is a standard error. Only available in debug build of Python.

msvcrt.OUT_TO_MSGBOX

  Error sink is a message box. Only available in debug build of Python.

msvcrt.REPORT_ERRMODE

  Report the current error mode value. Only available in debug build of Python.

msvcrt.CrtSetReportMode(type, mode)

  Specifies the destination or destinations for a specific report type generated by `_CrtDbgReport()` in the MS VC++ runtime. type must be one of the `CRT_*` constants listed below. mode must be one of the `CRTDBG_*` constants listed below. Only available in debug build of Python.

msvcrt.CrtSetReportFile(type, file)

  After you use `CrtSetReportMode()` to specify `CRTDBG_MODE_FILE`, you can specify the file handle to receive the message text. type must be one of the `CRT_*` constants listed below. file should be the file handle your want specified. Only available in debug build of Python.

msvcrt.CRT_WARN

  Warnings, messages, and information that doesn’t need immediate attention.

msvcrt.CRT_ERROR

  Errors, unrecoverable problems, and issues that require immediate attention.

msvcrt.CRT_ASSERT

  Assertion failures.

msvcrt.CRTDBG_MODE_DEBUG

  Writes the message to the debugger’s output window.

msvcrt.CRTDBG_MODE_FILE

  Writes the message to a user-supplied file handle. `CrtSetReportFile()` should be called to define the specific file or stream to use as the destination.

msvcrt.CRTDBG_MODE_WNDW

  Creates a message box to display the message along with the `Abort`, `Retry`, and `Ignore` buttons.

msvcrt.CRTDBG_REPORT_MODE

  Returns current mode for the specified type.

msvcrt.CRT_ASSEMBLY_VERSION

  The CRT Assembly version, from the `crtassem.h` header file.

msvcrt.VC_ASSEMBLY_PUBLICKEYTOKEN

  The VC Assembly public key token, from the `crtassem.h` header file.

msvcrt.LIBRARIES_ASSEMBLY_NAME_PREFIX

  The Libraries Assembly name prefix, from the `crtassem.h` header file.