# fcntl - pydoc - phpman

Help on built-in module fcntl:

## NAME
    fcntl

## DESCRIPTION
    This module performs file control and I/O control on file
    descriptors.  It is an interface to the fcntl() and ioctl() Unix
    routines.  File descriptors can be obtained with the fileno() method of
    a file or socket object.

## FUNCTIONS
### fcntl
        Perform the operation `cmd` on file descriptor fd.

        The values used for `cmd` are operating system dependent, and are available
        as constants in the fcntl module, using the same names as used in
        the relevant C header files.  The argument arg is optional, and
        defaults to 0; it may be an int or a string.  If arg is given as a string,
        the return value of fcntl is a string of that length, containing the
        resulting value put in the arg buffer by the operating system.  The length
        of the arg string is not allowed to exceed 1024 bytes.  If the arg given
        is an integer or if none is specified, the result value is an integer
        corresponding to the return value of the fcntl call in the C code.

### flock
        Perform the lock operation `operation` on file descriptor `fd`.

        See the Unix manual page for [flock(2)](https://www.chedong.com/phpMan.php/man/flock/2/markdown) for details (On some systems, this
        function is emulated using fcntl()).

### ioctl
        Perform the operation `request` on file descriptor `fd`.

        The values used for `request` are operating system dependent, and are available
        as constants in the fcntl or termios library modules, using the same names as
        used in the relevant C header files.

        The argument `arg` is optional, and defaults to 0; it may be an int or a
        buffer containing character data (most likely a string or an array).

        If the argument is a mutable buffer (such as an array) and if the
        mutate_flag argument (which is only allowed in this case) is true then the
        buffer is (in effect) passed to the operating system and changes made by
        the OS will be reflected in the contents of the buffer after the call has
        returned.  The return value is the integer returned by the ioctl system
        call.

        If the argument is a mutable buffer and the mutable_flag argument is false,
        the behavior is as if a string had been passed.

        If the argument is an immutable buffer (most likely a string) then a copy
        of the buffer is passed to the operating system and the return value is a
        string of the same length containing whatever the operating system put in
        the buffer.  The length of the arg buffer in this case is not allowed to
        exceed 1024 bytes.

        If the arg given is an integer or if none is specified, the result value is
        an integer corresponding to the return value of the ioctl call in the C
        code.

### lockf
        A wrapper around the fcntl() locking calls.

        `fd` is the file descriptor of the file to lock or unlock, and operation is one
        of the following values:

            LOCK_UN - unlock
            LOCK_SH - acquire a shared lock
            LOCK_EX - acquire an exclusive lock

        When operation is LOCK_SH or LOCK_EX, it can also be bitwise ORed with
        LOCK_NB to avoid blocking on lock acquisition.  If LOCK_NB is used and the
        lock cannot be acquired, an OSError will be raised and the exception will
        have an errno attribute set to EACCES or EAGAIN (depending on the operating
        system -- for portability, check for either value).

        `len` is the number of bytes to lock, with the default meaning to lock to
        EOF.  `start` is the byte offset, relative to `whence`, to that the lock
        starts.  `whence` is as with fileobj.seek(), specifically:

            0 - relative to the start of the file (SEEK_SET)
            1 - relative to the current buffer position (SEEK_CUR)
            2 - relative to the end of the file (SEEK_END)

## DATA
    DN_ACCESS = 1
    DN_ATTRIB = 32
    DN_CREATE = 4
    DN_DELETE = 8
    DN_MODIFY = 2
    DN_MULTISHOT = 2147483648
    DN_RENAME = 16
    FASYNC = 8192
    FD_CLOEXEC = 1
    F_ADD_SEALS = 1033
    F_DUPFD = 0
    F_DUPFD_CLOEXEC = 1030
    F_EXLCK = 4
    F_GETFD = 1
    F_GETFL = 3
    F_GETLEASE = 1025
    F_GETLK = 5
    F_GETLK64 = 5
    F_GETOWN = 9
    F_GETPIPE_SZ = 1032
    F_GETSIG = 11
    F_GET_SEALS = 1034
    F_NOTIFY = 1026
    F_OFD_GETLK = 36
    F_OFD_SETLK = 37
    F_OFD_SETLKW = 38
    F_RDLCK = 0
    F_SEAL_GROW = 4
    F_SEAL_SEAL = 1
    F_SEAL_SHRINK = 2
    F_SEAL_WRITE = 8
    F_SETFD = 2
    F_SETFL = 4
    F_SETLEASE = 1024
    F_SETLK = 6
    F_SETLK64 = 6
    F_SETLKW = 7
    F_SETLKW64 = 7
    F_SETOWN = 8
    F_SETPIPE_SZ = 1031
    F_SETSIG = 10
    F_SHLCK = 8
    F_UNLCK = 2
    F_WRLCK = 1
    LOCK_EX = 2
    LOCK_MAND = 32
    LOCK_NB = 4
    LOCK_READ = 64
    LOCK_RW = 192
    LOCK_SH = 1
    LOCK_UN = 8
    LOCK_WRITE = 128

## FILE
    (built-in)