:mod:`curses` --- Terminal handling for character-cell displays

===============================================================

.. module:: curses

   :synopsis: An interface to the curses library, providing portable terminal handling.

.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>

.. sectionauthor:: Eric Raymond <esr@thyrsus.com>

.. versionchanged:: 1.6

   Added support for the ``ncurses`` library and converted to a package.

The :mod:`curses` module provides an interface to the curses library, the

de-facto standard for portable advanced terminal handling.

While curses is most widely used in the Unix environment, versions are available

for DOS, OS/2, and possibly other systems as well.  This extension module is

designed to match the API of ncurses, an open-source curses library hosted on

Linux and the BSD variants of Unix.

.. note::

   Since version 5.4, the ncurses library decides how to interpret non-ASCII data

   using the ``nl_langinfo`` function.  That means that you have to call

   :func:`locale.setlocale` in the application and encode Unicode strings

   using one of the system's available encodings.  This example uses the

   system's default encoding::

      import locale

      locale.setlocale(locale.LC_ALL, '')

      code = locale.getpreferredencoding()

   Then use *code* as the encoding for :meth:`str.encode` calls.

.. seealso::

   Module :mod:`curses.ascii`

      Utilities for working with ASCII characters, regardless of your locale settings.

   Module :mod:`curses.panel`

      A panel stack extension that adds depth to  curses windows.

   Module :mod:`curses.textpad`

      Editable text widget for curses supporting  :program:`Emacs`\ -like bindings.

   Module :mod:`curses.wrapper`

      Convenience function to ensure proper terminal setup and resetting on

      application entry and exit.

   :ref:`curses-howto`

      Tutorial material on using curses with Python, by Andrew Kuchling and Eric

      Raymond.

   The :file:`Demo/curses/` directory in the Python source distribution contains

   some example programs using the curses bindings provided by this module.

.. _curses-functions:

Functions

---------

The module :mod:`curses` defines the following exception:

.. exception:: error

   Exception raised when a curses library function returns an error.

.. note::

   Whenever *x* or *y* arguments to a function or a method are optional, they

   default to the current cursor location. Whenever *attr* is optional, it defaults

   to :const:`A_NORMAL`.

The module :mod:`curses` defines the following functions:

.. function:: baudrate()

   Returns the output speed of the terminal in bits per second.  On software

   terminal emulators it will have a fixed high value. Included for historical

   reasons; in former times, it was used to  write output loops for time delays and

   occasionally to change interfaces depending on the line speed.

.. function:: beep()

   Emit a short attention sound.

.. function:: can_change_color()

   Returns true or false, depending on whether the programmer can change the colors

   displayed by the terminal.

.. function:: cbreak()

   Enter cbreak mode.  In cbreak mode (sometimes called "rare" mode) normal tty

   line buffering is turned off and characters are available to be read one by one.

   However, unlike raw mode, special characters (interrupt, quit, suspend, and flow

   control) retain their effects on the tty driver and calling program.  Calling

   first :func:`raw` then :func:`cbreak` leaves the terminal in cbreak mode.

.. function:: color_content(color_number)

   Returns the intensity of the red, green, and blue (RGB) components in the color

   *color_number*, which must be between ``0`` and :const:`COLORS`.  A 3-tuple is

   returned, containing the R,G,B values for the given color, which will be between

   ``0`` (no component) and ``1000`` (maximum amount of component).

.. function:: color_pair(color_number)

   Returns the attribute value for displaying text in the specified color.  This

   attribute value can be combined with :const:`A_STANDOUT`, :const:`A_REVERSE`,

   and the other :const:`A_\*` attributes.  :func:`pair_number` is the counterpart

   to this function.

.. function:: curs_set(visibility)

   Sets the cursor state.  *visibility* can be set to 0, 1, or 2, for invisible,

   normal, or very visible.  If the terminal supports the visibility requested, the

   previous cursor state is returned; otherwise, an exception is raised.  On many

   terminals, the "visible" mode is an underline cursor and the "very visible" mode

   is a block cursor.

.. function:: def_prog_mode()

   Saves the current terminal mode as the "program" mode, the mode when the running

   program is using curses.  (Its counterpart is the "shell" mode, for when the

   program is not in curses.)  Subsequent calls to :func:`reset_prog_mode` will

   restore this mode.

.. function:: def_shell_mode()

   Saves the current terminal mode as the "shell" mode, the mode when the running

   program is not using curses.  (Its counterpart is the "program" mode, when the

   program is using curses capabilities.) Subsequent calls to

   :func:`reset_shell_mode` will restore this mode.

.. function:: delay_output(ms)

   Inserts an *ms* millisecond pause in output.

.. function:: doupdate()

   Update the physical screen.  The curses library keeps two data structures, one

   representing the current physical screen contents and a virtual screen

   representing the desired next state.  The :func:`doupdate` ground updates the

   physical screen to match the virtual screen.

   The virtual screen may be updated by a :meth:`noutrefresh` call after write

   operations such as :meth:`addstr` have been performed on a window.  The normal

   :meth:`refresh` call is simply :meth:`noutrefresh` followed by :func:`doupdate`;

   if you have to update multiple windows, you can speed performance and perhaps

   reduce screen flicker by issuing :meth:`noutrefresh` calls on all windows,

   followed by a single :func:`doupdate`.

.. function:: echo()

   Enter echo mode.  In echo mode, each character input is echoed to the screen as

   it is entered.

.. function:: endwin()

   De-initialize the library, and return terminal to normal status.

.. function:: erasechar()

   Returns the user's current erase character.  Under Unix operating systems this

   is a property of the controlling tty of the curses program, and is not set by

   the curses library itself.

.. function:: filter()

   The :func:`filter` routine, if used, must be called before :func:`initscr` is

   called.  The effect is that, during those calls, LINES is set to 1; the

   capabilities clear, cup, cud, cud1, cuu1, cuu, vpa are disabled; and the home

   string is set to the value of cr. The effect is that the cursor is confined to

   the current line, and so are screen updates.  This may be used for enabling

   character-at-a-time  line editing without touching the rest of the screen.

.. function:: flash()

   Flash the screen.  That is, change it to reverse-video and then change it back

   in a short interval.  Some people prefer such as 'visible bell' to the audible

   attention signal produced by :func:`beep`.

.. function:: flushinp()

   Flush all input buffers.  This throws away any  typeahead  that  has been typed

   by the user and has not yet been processed by the program.

.. function:: getmouse()

   After :meth:`getch` returns :const:`KEY_MOUSE` to signal a mouse event, this

   method should be call to retrieve the queued mouse event, represented as a

   5-tuple ``(id, x, y, z, bstate)``. *id* is an ID value used to distinguish

   multiple devices, and *x*, *y*, *z* are the event's coordinates.  (*z* is

   currently unused.).  *bstate* is an integer value whose bits will be set to

   indicate the type of event, and will be the bitwise OR of one or more of the

   following constants, where *n* is the button number from 1 to 4:

   :const:`BUTTONn_PRESSED`, :const:`BUTTONn_RELEASED`, :const:`BUTTONn_CLICKED`,

   :const:`BUTTONn_DOUBLE_CLICKED`, :const:`BUTTONn_TRIPLE_CLICKED`,

   :const:`BUTTON_SHIFT`, :const:`BUTTON_CTRL`, :const:`BUTTON_ALT`.

.. function:: getsyx()

   Returns the current coordinates of the virtual screen cursor in y and x.  If

   leaveok is currently true, then -1,-1 is returned.

.. function:: getwin(file)

   Reads window related data stored in the file by an earlier :func:`putwin` call.

   The routine then creates and initializes a new window using that data, returning

   the new window object.

.. function:: has_colors()

   Returns true if the terminal can display colors; otherwise, it returns false.

.. function:: has_ic()

   Returns true if the terminal has insert- and delete- character capabilities.

   This function is included for historical reasons only, as all modern software

   terminal emulators have such capabilities.

.. function:: has_il()

   Returns true if the terminal has insert- and delete-line  capabilities,  or  can

   simulate  them  using scrolling regions. This function is included for

   historical reasons only, as all modern software terminal emulators have such

   capabilities.

.. function:: has_key(ch)

   Takes a key value *ch*, and returns true if the current terminal type recognizes

   a key with that value.

.. function:: halfdelay(tenths)

   Used for half-delay mode, which is similar to cbreak mode in that characters

   typed by the user are immediately available to the program. However, after

   blocking for *tenths* tenths of seconds, an exception is raised if nothing has

   been typed.  The value of *tenths* must be a number between 1 and 255.  Use

   :func:`nocbreak` to leave half-delay mode.

.. function:: init_color(color_number, r, g, b)

   Changes the definition of a color, taking the number of the color to be changed

   followed by three RGB values (for the amounts of red, green, and blue

   components).  The value of *color_number* must be between ``0`` and

   :const:`COLORS`.  Each of *r*, *g*, *b*, must be a value between ``0`` and

   ``1000``.  When :func:`init_color` is used, all occurrences of that color on the

   screen immediately change to the new definition.  This function is a no-op on

   most terminals; it is active only if :func:`can_change_color` returns ``1``.

.. function:: init_pair(pair_number, fg, bg)

   Changes the definition of a color-pair.  It takes three arguments: the number of

   the color-pair to be changed, the foreground color number, and the background

   color number.  The value of *pair_number* must be between ``1`` and

   ``COLOR_PAIRS - 1`` (the ``0`` color pair is wired to white on black and cannot

   be changed).  The value of *fg* and *bg* arguments must be between ``0`` and

   :const:`COLORS`.  If the color-pair was previously initialized, the screen is

   refreshed and all occurrences of that color-pair are changed to the new

   definition.

.. function:: initscr()

   Initialize the library. Returns a :class:`WindowObject` which represents the

   whole screen.

   .. note::

      If there is an error opening the terminal, the underlying curses library may

      cause the interpreter to exit.

.. function:: isendwin()

   Returns true if :func:`endwin` has been called (that is, the  curses library has

   been deinitialized).

.. function:: keyname(k)

   Return the name of the key numbered *k*.  The name of a key generating printable

   ASCII character is the key's character.  The name of a control-key combination

   is a two-character string consisting of a caret followed by the corresponding

   printable ASCII character.  The name of an alt-key combination (128-255) is a

   string consisting of the prefix 'M-' followed by the name of the corresponding

   ASCII character.

.. function:: killchar()

   Returns the user's current line kill character. Under Unix operating systems

   this is a property of the controlling tty of the curses program, and is not set

   by the curses library itself.

.. function:: longname()

   Returns a string containing the terminfo long name field describing the current

   terminal.  The maximum length of a verbose description is 128 characters.  It is

   defined only after the call to :func:`initscr`.

.. function:: meta(yes)

   If *yes* is 1, allow 8-bit characters to be input. If *yes* is 0,  allow only

   7-bit chars.

.. function:: mouseinterval(interval)

   Sets the maximum time in milliseconds that can elapse between press and release

   events in order for them to be recognized as a click, and returns the previous

   interval value.  The default value is 200 msec, or one fifth of a second.

.. function:: mousemask(mousemask)

   Sets the mouse events to be reported, and returns a tuple ``(availmask,

   oldmask)``.   *availmask* indicates which of the specified mouse events can be

   reported; on complete failure it returns 0.  *oldmask* is the previous value of

   the given window's mouse event mask.  If this function is never called, no mouse

   events are ever reported.

.. function:: napms(ms)

   Sleep for *ms* milliseconds.

.. function:: newpad(nlines, ncols)

   Creates and returns a pointer to a new pad data structure with the given number

   of lines and columns.  A pad is returned as a window object.

   A pad is like a window, except that it is not restricted by the screen size, and

   is not necessarily associated with a particular part of the screen.  Pads can be

   used when a large window is needed, and only a part of the window will be on the

   screen at one time.  Automatic refreshes of pads (such as from scrolling or

   echoing of input) do not occur.  The :meth:`refresh` and :meth:`noutrefresh`

   methods of a pad require 6 arguments to specify the part of the pad to be

   displayed and the location on the screen to be used for the display. The

   arguments are pminrow, pmincol, sminrow, smincol, smaxrow, smaxcol; the p

   arguments refer to the upper left corner of the pad region to be displayed and

   the s arguments define a clipping box on the screen within which the pad region

   is to be displayed.

.. function:: newwin([nlines, ncols,] begin_y, begin_x)

   Return a new window, whose left-upper corner is at  ``(begin_y, begin_x)``, and

   whose height/width is  *nlines*/*ncols*.

   By default, the window will extend from the  specified position to the lower

   right corner of the screen.

.. function:: nl()

   Enter newline mode.  This mode translates the return key into newline on input,

   and translates newline into return and line-feed on output. Newline mode is

   initially on.

.. function:: nocbreak()

   Leave cbreak mode.  Return to normal "cooked" mode with line buffering.

.. function:: noecho()

   Leave echo mode.  Echoing of input characters is turned off.

.. function:: nonl()

   Leave newline mode.  Disable translation of return into newline on input, and

   disable low-level translation of newline into newline/return on output (but this

   does not change the behavior of ``addch('\n')``, which always does the

   equivalent of return and line feed on the virtual screen).  With translation

   off, curses can sometimes speed up vertical motion a little; also, it will be

   able to detect the return key on input.

.. function:: noqiflush()

   When the noqiflush routine is used, normal flush of input and output queues

   associated with the INTR, QUIT and SUSP characters will not be done.  You may

   want to call :func:`noqiflush` in a signal handler if you want output to

   continue as though the interrupt had not occurred, after the handler exits.

.. function:: noraw()

   Leave raw mode. Return to normal "cooked" mode with line buffering.

.. function:: pair_content(pair_number)

   Returns a tuple ``(fg, bg)`` containing the colors for the requested color pair.

   The value of *pair_number* must be between ``1`` and ``COLOR_PAIRS - 1``.

.. function:: pair_number(attr)

   Returns the number of the color-pair set by the attribute value *attr*.

   :func:`color_pair` is the counterpart to this function.

.. function:: putp(string)

   Equivalent to ``tputs(str, 1, putchar)``; emits the value of a specified

   terminfo capability for the current terminal.  Note that the output of putp

   always goes to standard output.

.. function:: qiflush( [flag] )

   If *flag* is false, the effect is the same as calling :func:`noqiflush`. If

   *flag* is true, or no argument is provided, the queues will be flushed when

   these control characters are read.

.. function:: raw()

   Enter raw mode.  In raw mode, normal line buffering and  processing of

   interrupt, quit, suspend, and flow control keys are turned off; characters are

   presented to curses input functions one by one.

.. function:: reset_prog_mode()

   Restores the  terminal  to "program" mode, as previously saved  by

   :func:`def_prog_mode`.

.. function:: reset_shell_mode()

   Restores the  terminal  to "shell" mode, as previously saved  by

   :func:`def_shell_mode`.

.. function:: setsyx(y, x)

   Sets the virtual screen cursor to *y*, *x*. If *y* and *x* are both -1, then

   leaveok is set.

.. function:: setupterm([termstr, fd])

   Initializes the terminal.  *termstr* is a string giving the terminal name; if

   omitted, the value of the TERM environment variable will be used.  *fd* is the

   file descriptor to which any initialization sequences will be sent; if not

   supplied, the file descriptor for ``sys.stdout`` will be used.

.. function:: start_color()

   Must be called if the programmer wants to use colors, and before any other color

   manipulation routine is called.  It is good practice to call this routine right

   after :func:`initscr`.

   :func:`start_color` initializes eight basic colors (black, red,  green, yellow,

   blue, magenta, cyan, and white), and two global variables in the :mod:`curses`

   module, :const:`COLORS` and :const:`COLOR_PAIRS`, containing the maximum number

   of colors and color-pairs the terminal can support.  It also restores the colors

   on the terminal to the values they had when the terminal was just turned on.

.. function:: termattrs()

   Returns a logical OR of all video attributes supported by the terminal.  This

   information is useful when a curses program needs complete control over the

   appearance of the screen.

.. function:: termname()

   Returns the value of the environment variable TERM, truncated to 14 characters.

.. function:: tigetflag(capname)

   Returns the value of the Boolean capability corresponding to the terminfo

   capability name *capname*.  The value ``-1`` is returned if *capname* is not a

   Boolean capability, or ``0`` if it is canceled or absent from the terminal

   description.

.. function:: tigetnum(capname)

   Returns the value of the numeric capability corresponding to the terminfo

   capability name *capname*.  The value ``-2`` is returned if *capname* is not a

   numeric capability, or ``-1`` if it is canceled or absent from the terminal

   description.