The Tor Browser: python/blessings/README.rst@b8a032363ba2 (annotated)

python/blessings/README.rst@b8a032363ba2 (annotated)

python/blessings/README.rst

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 =========
 Blessings
 =========
 Coding with Blessings looks like this... ::
     from blessings import Terminal
     t = Terminal()
     print t.bold('Hi there!')
     print t.bold_red_on_bright_green('It hurts my eyes!')
     with t.location(0, t.height - 1):
         print 'This is at the bottom.'
 Or, for byte-level control, you can drop down and play with raw terminal
 capabilities::
     print '{t.bold}All your {t.red}bold and red base{t.normal}'.format(t=t)
     print t.wingo(2)
 The Pitch
 =========
 Blessings lifts several of curses_' limiting assumptions, and it makes your
 code pretty, too:
 * Use styles, color, and maybe a little positioning without clearing the whole
   screen first.
 * Leave more than one screenful of scrollback in the buffer after your program
   exits, like a well-behaved command-line app should.
 * Get rid of all those noisy, C-like calls to ``tigetstr`` and ``tparm``, so
   your code doesn't get crowded out by terminal bookkeeping.
 * Act intelligently when somebody redirects your output to a file, omitting the
   terminal control codes the user doesn't want to see (optional).
 .. _curses: http://docs.python.org/library/curses.html
 Before And After
 ----------------
 Without Blessings, this is how you'd print some underlined text at the bottom
 of the screen::
     from curses import tigetstr, setupterm, tparm
     from fcntl import ioctl
     from os import isatty
     import struct
     import sys
     from termios import TIOCGWINSZ
     # If we want to tolerate having our output piped to other commands or
     # files without crashing, we need to do all this branching:
     if hasattr(sys.stdout, 'fileno') and isatty(sys.stdout.fileno()):
         setupterm()
         sc = tigetstr('sc')
         cup = tigetstr('cup')
         rc = tigetstr('rc')
         underline = tigetstr('smul')
         normal = tigetstr('sgr0')
     else:
         sc = cup = rc = underline = normal = ''
     print sc  # Save cursor position.
     if cup:
         # tigetnum('lines') doesn't always update promptly, hence this:
         height = struct.unpack('hhhh', ioctl(0, TIOCGWINSZ, '\000' * 8))[0]
         print tparm(cup, height - 1, 0)  # Move cursor to bottom.
     print 'This is {under}underlined{normal}!'.format(under=underline,
                                                       normal=normal)
     print rc  # Restore cursor position.
 Phew! That was long and full of incomprehensible trash! Let's try it again,
 this time with Blessings::
     from blessings import Terminal
     term = Terminal()
     with term.location(0, term.height - 1):
         print 'This is', term.underline('pretty!')
 Much better.
 What It Provides
 ================
 Blessings provides just one top-level object: ``Terminal``. Instantiating a
 ``Terminal`` figures out whether you're on a terminal at all and, if so, does
 any necessary terminal setup. After that, you can proceed to ask it all sorts
 of things about the terminal. Terminal terminal terminal.
 Simple Formatting
 -----------------
 Lots of handy formatting codes ("capabilities" in low-level parlance) are
 available as attributes on a ``Terminal``. For example::
     from blessings import Terminal
     term = Terminal()
     print 'I am ' + term.bold + 'bold' + term.normal + '!'
 You can also use them as wrappers so you don't have to say ``normal``
 afterward::
     print 'I am', term.bold('bold') + '!'
 Or, if you want fine-grained control while maintaining some semblance of
 brevity, you can combine it with Python's string formatting, which makes
 attributes easy to access::
     print 'All your {t.red}base {t.underline}are belong to us{t.normal}'.format(t=term)
 Simple capabilities of interest include...
 * ``bold``
 * ``reverse``
 * ``underline``
 * ``no_underline`` (which turns off underlining)
 * ``blink``
 * ``normal`` (which turns off everything, even colors)
 * ``clear_eol`` (clear to the end of the line)
 * ``clear_bol`` (clear to beginning of line)
 * ``clear_eos`` (clear to end of screen)
 Here are a few more which are less likely to work on all terminals:
 * ``dim``
 * ``italic`` and ``no_italic``
 * ``shadow`` and ``no_shadow``
 * ``standout`` and ``no_standout``
 * ``subscript`` and ``no_subscript``
 * ``superscript`` and ``no_superscript``
 * ``flash`` (which flashes the screen once)
 Note that, while the inverse of ``underline`` is ``no_underline``, the only way
 to turn off ``bold`` or ``reverse`` is ``normal``, which also cancels any
 custom colors. This is because there's no way to tell the terminal to undo
 certain pieces of formatting, even at the lowest level.
 You might notice that the above aren't the typical incomprehensible terminfo
 capability names; we alias a few of the harder-to-remember ones for
 readability. However, you aren't limited to these: you can reference any
 string-returning capability listed on the `terminfo man page`_ by the name
 under the "Cap-name" column: for example, ``term.rum``.
 .. _`terminfo man page`: http://www.manpagez.com/man/5/terminfo/
 Color
 -----
 colors, both foreground and background, are available as easy-to-remember
 attributes::
     from blessings import Terminal
     term = Terminal()
     print term.red + term.on_green + 'Red on green? Ick!' + term.normal
     print term.bright_red + term.on_bright_blue + 'This is even worse!' + term.normal
 You can also call them as wrappers, which sets everything back to normal at the
 end::
     print term.red_on_green('Red on green? Ick!')
     print term.yellow('I can barely see it.')
 The available colors are...
 * ``black``
 * ``red``
 * ``green``
 * ``yellow``
 * ``blue``
 * ``magenta``
 * ``cyan``
 * ``white``
 You can set the background color instead of the foreground by prepending
 ``on_``, as in ``on_blue``. There is also a ``bright`` version of each color:
 for example, ``on_bright_blue``.
 There is also a numerical interface to colors, which takes an integer from
 -15::
     term.color(5) + 'Hello' + term.normal
     term.on_color(3) + 'Hello' + term.normal
     term.color(5)('Hello')
     term.on_color(3)('Hello')
 If some color is unsupported (for instance, if only the normal colors are
 available, not the bright ones), trying to use it will, on most terminals, have
 no effect: the foreground and background colors will stay as they were. You can
 get fancy and do different things depending on the supported colors by checking
 `number_of_colors`_.
 .. _`number_of_colors`: http://packages.python.org/blessings/#blessings.Terminal.number_of_colors
 Compound Formatting
 -------------------
 If you want to do lots of crazy formatting all at once, you can just mash it
 all together::
     from blessings import Terminal
     term = Terminal()
     print term.bold_underline_green_on_yellow + 'Woo' + term.normal
 Or you can use your newly coined attribute as a wrapper, which implicitly sets
 everything back to normal afterward::
     print term.bold_underline_green_on_yellow('Woo')
 This compound notation comes in handy if you want to allow users to customize
 the formatting of your app: just have them pass in a format specifier like
 "bold_green" on the command line, and do a quick ``getattr(term,
 that_option)('Your text')`` when you do your formatting.
 I'd be remiss if I didn't credit couleur_, where I probably got the idea for
 all this mashing.
 .. _couleur: http://pypi.python.org/pypi/couleur
 Parametrized Capabilities
 -------------------------
 Some capabilities take parameters. Rather than making you dig up ``tparm()``
 all the time, we simply make such capabilities into callable strings. You can
 pass the parameters right in::
     from blessings import Terminal
     term = Terminal()
     print term.move(10, 1)
 Here are some of interest:
 ``move``
   Position the cursor elsewhere. Parameters are y coordinate, then x
   coordinate.
 ``move_x``
   Move the cursor to the given column.
 ``move_y``
   Move the cursor to the given row.
 You can also reference any other string-returning capability listed on the
 `terminfo man page`_ by its name under the "Cap-name" column.
 .. _`terminfo man page`: http://www.manpagez.com/man/5/terminfo/
 Height and Width
 ----------------
 It's simple to get the height and width of the terminal, in characters::
     from blessings import Terminal
     term = Terminal()
     height = term.height
     width = term.width
 These are newly updated each time you ask for them, so they're safe to use from
 SIGWINCH handlers.
 Temporary Repositioning
 -----------------------
 Sometimes you need to flit to a certain location, print something, and then
 return: for example, when updating a progress bar at the bottom of the screen.
 ``Terminal`` provides a context manager for doing this concisely::
     from blessings import Terminal
     term = Terminal()
     with term.location(0, term.height - 1):
         print 'Here is the bottom.'
     print 'This is back where I came from.'
 Parameters to ``location()`` are ``x`` and then ``y``, but you can also pass
 just one of them, leaving the other alone. For example... ::
     with term.location(y=10):
         print 'We changed just the row.'
 If you want to reposition permanently, see ``move``, in an example above.
 Pipe Savvy
 ----------
 If your program isn't attached to a terminal, like if it's being piped to
 another command or redirected to a file, all the capability attributes on
 ``Terminal`` will return empty strings. You'll get a nice-looking file without
 any formatting codes gumming up the works.
 If you want to override this--like if you anticipate your program being piped
 through ``less -r``, which handles terminal escapes just fine--pass
 ``force_styling=True`` to the ``Terminal`` constructor.
 In any case, there is an ``is_a_tty`` attribute on ``Terminal`` that lets you
 see whether the attached stream seems to be a terminal. If it's false, you
 might refrain from drawing progress bars and other frippery, since you're
 apparently headed into a pipe::
     from blessings import Terminal
     term = Terminal()
     if term.is_a_tty:
         with term.location(0, term.height - 1):
             print 'Progress: [=======>   ]'
     print term.bold('Important stuff')
 Shopping List
 =============
 There are decades of legacy tied up in terminal interaction, so attention to
 detail and behavior in edge cases make a difference. Here are some ways
 Blessings has your back:
 * Uses the terminfo database so it works with any terminal type
 * Provides up-to-the-moment terminal height and width, so you can respond to
   terminal size changes (SIGWINCH signals). (Most other libraries query the
   ``COLUMNS`` and ``LINES`` environment variables or the ``cols`` or ``lines``
   terminal capabilities, which don't update promptly, if at all.)
 * Avoids making a mess if the output gets piped to a non-terminal
 * Works great with standard Python string templating
 * Provides convenient access to all terminal capabilities, not just a sugared
   few
 * Outputs to any file-like object, not just stdout
 * Keeps a minimum of internal state, so you can feel free to mix and match with
   calls to curses or whatever other terminal libraries you like
 Blessings does not provide...
 * Native color support on the Windows command prompt. However, it should work
   when used in concert with colorama_.
 .. _colorama: http://pypi.python.org/pypi/colorama/0.2.4
 Bugs
 ====
 Bugs or suggestions? Visit the `issue tracker`_.
 .. _`issue tracker`: https://github.com/erikrose/blessings/issues/new
 License
 =======
 Blessings is under the MIT License. See the LICENSE file.
 Version History
 ===============
 .3
   * Add ``number_of_colors``, which tells you how many colors the terminal
     supports.
   * Made ``color(n)`` and ``on_color(n)`` callable to wrap a string, like the
     named colors can. Also, make them both fall back to the ``setf`` and
     ``setb`` capabilities (like the named colors do) if the ANSI ``setaf`` and
     ``setab`` aren't available.
   * Allow ``color`` attr to act as an unparametrized string, not just a
     callable.
   * Make ``height`` and ``width`` examine any passed-in stream before falling
     back to stdout. (This rarely if ever affects actual behavior; it's mostly
     philosophical.)
   * Make caching simpler and slightly more efficient.
   * Get rid of a reference cycle between Terminals and FormattingStrings.
   * Update docs to reflect that terminal addressing (as in ``location()``) is
 -based.
 .2
   * Added support for Python 3! We need 3.2.3 or greater, because the curses
     library couldn't decide whether to accept strs or bytes before that
     (http://bugs.python.org/issue10570).
   * Everything that comes out of the library is now unicode. This lets us
     support Python 3 without making a mess of the code, and Python 2 should
     continue to work unless you were testing types (and badly). Please file a
     bug if this causes trouble for you.
   * Changed to the MIT License for better world domination.
   * Added Sphinx docs.
 .1
   * Added nicely named attributes for colors.
   * Introduced compound formatting.
   * Added wrapper behavior for styling and colors.
   * Let you force capabilities to be non-empty, even if the output stream is
     not a terminal.
   * Added the ``is_a_tty`` attribute for telling whether the output stream is a
     terminal.
   * Sugared the remaining interesting string capabilities.
   * Let ``location()`` operate on just an x *or* y coordinate.
 .0
   * Extracted Blessings from nose-progressive, my `progress-bar-having,
     traceback-shortcutting, rootin', tootin' testrunner`_. It provided the
     tootin' functionality.
 .. _`progress-bar-having, traceback-shortcutting, rootin', tootin' testrunner`: http://pypi.python.org/pypi/nose-progressive/

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