blessings 1.7

Description:

blessings 1.7

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)
Full API Reference

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 necessarily
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).


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.
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 + '!'
Though they are strings at heart, you can also use them as callable 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)

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 portable way to tell the terminal to
undo certain pieces of formatting, even at the lowest level.
You might also 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.


Color
16 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
0-15:
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.


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.


Moving The Cursor
When you want to move the cursor to output text at a specific spot, you have
a few choices.

Moving Temporarily
Most often, you’ll 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’re doing a series of move calls (see below) and want to return the
cursor to its original position afterward, call location() with no
arguments, and it will do only the position restoring:
with term.location():
print term.move(1, 1) + 'Hi'
print term.move(9, 9) + 'Mom'
Note that, since location() uses the terminal’s built-in
position-remembering machinery, you can’t usefully nest multiple calls. Use
location() at the outermost spot, and use simpler things like move
inside.


Moving Permanently
If you just want to move and aren’t worried about returning, do something like
this:
from blessings import Terminal

term = Terminal()
print term.move(10, 1) + 'Hi, mom!'

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.


How does all this work? These are simply more terminal capabilities, wrapped to
give them nicer names. The added wrinkle–that they take parameters–is also
given a pleasant treatment: rather than making you dig up tparm() all the
time, we simply make these capabilities into callable strings. You’d get the
raw capability strings if you were to just print them, but they’re fully
parametrized if you pass params to them as if they were functions.
Consequently, you can also reference any other string-returning capability
listed on the terminfo man page by its name under the “Cap-name” column.


One-Notch Movement
Finally, there are some parameterless movement capabilities that move the
cursor one character in various directions:

move_left
move_right
move_up
move_down

For example…
print term.move_up + 'Howdy!'



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.


Clearing The Screen
Blessings provides syntactic sugar over some screen-clearing capabilities:

clear
Clear the whole screen.

clear_eol
Clear to the end of the line.

clear_bol
Clear backward to the beginning of the line.

clear_eos
Clear to the end of screen.




Full-Screen Mode
Perhaps you have seen a full-screen program, such as an editor, restore the
exact previous state of the terminal upon exiting, including, for example, the
command-line prompt from which it was launched. Curses pretty much forces you
into this behavior, but Blessings makes it optional. If you want to do the
state-restoration thing, use these capabilities:

enter_fullscreen
Switch to the terminal mode where full-screen output is sanctioned. Print
this before you do any output.

exit_fullscreen
Switch back to normal mode, restoring the exact state from before
enter_fullscreen was used.


Using exit_fullscreen will wipe away any trace of your program’s output, so
reserve it for when you don’t want to leave anything behind in the scrollback.
There’s also a context manager you can use as a shortcut:
from blessings import Terminal

term = Terminal()
with term.fullscreen():
# Print some stuff.
Besides brevity, another advantage is that it switches back to normal mode even
if an exception is raised in the with block.


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 a does_styling attribute on Terminal that lets
you see whether your capabilities will return actual, working formatting codes.
If it’s false, you should refrain from drawing progress bars and other frippery
and just stick to content, since you’re apparently headed into a pipe:
from blessings import Terminal

term = Terminal()
if term.does_styling:
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.



Bugs
Bugs or suggestions? Visit the issue tracker.
Blessings tests are run automatically by Travis CI.



License
Blessings is under the MIT License. See the LICENSE file.


Version History

1.7

Drop support for Python 2.6 and 3.3, which are end-of-lifed.
Switch from 2to3 to the six library.


1.6.1

Don’t crash if number_of_colors() is called when run in a non-terminal
or when does_styling is otherwise false.


1.6

Add does_styling property. This takes force_styling into account
and should replace most uses of is_a_tty.
Make is_a_tty a read-only property, like does_styling. Writing to
it never would have done anything constructive.
Add fullscreen() and hidden_cursor() to the auto-generated docs.
Fall back to LINES and COLUMNS environment vars to find height and
width. (jquast)
Support terminal types, such as kermit and avatar, that use bytes 127-255
in their escape sequences. (jquast)


1.5.1

Clean up fabfile, removing the redundant test command.
Add Travis support.
Make python setup.py test work without spurious errors on 2.6.
Work around a tox parsing bug in its config file.
Make context managers clean up after themselves even if there’s an
exception. (Vitja Makarov)
Parametrizing a capability no longer crashes when there is no tty. (Vitja
Makarov)


1.5

Add syntactic sugar and documentation for enter_fullscreen and
exit_fullscreen.
Add context managers fullscreen() and hidden_cursor().
Now you can force a Terminal never to emit styles by passing
force_styling=None.


1.4

Add syntactic sugar for cursor visibility control and single-space-movement
capabilities.
Endorse the location() idiom for restoring cursor position after a
series of manual movements.
Fix a bug in which location() wouldn’t do anything when passed zeroes.
Allow tests to be run with python setup.py test.


1.3

Added 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.
Allowed color attr to act as an unparametrized string, not just a
callable.
Made height and width examine any passed-in stream before falling
back to stdout. (This rarely if ever affects actual behavior; it’s mostly
philosophical.)
Made caching simpler and slightly more efficient.
Got rid of a reference cycle between Terminals and FormattingStrings.
Updated docs to reflect that terminal addressing (as in location()) is
0-based.


1.2

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.


1.1

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.


1.0

Extracted Blessings from nose-progressive, my progress-bar-having,
traceback-shortcutting, rootin’, tootin’ testrunner. It provided the
tootin’ functionality.