As usual, do this assignment on the SEASnet GNU/Linux servers lnxsrv11, lnxsrv12, lnxsrv13, and lnxsrv15, with /usr/local/cs/bin prepended to your PATH.
If you need a hint, ask a TA or an LA. This assignment is not intended to be done without any hints.
The basic idea here is to get a mental model of how Emacs works by looking at a bit of its keybindings and source code.
Start up a fresh Emacs with a *scratch* buffer.
To warm up, compute 234 (i.e., 2**(3**4)) in the *scratch* buffer, by using the expt function. Use Emacs to determine whether this number fits into a 64-bit signed integer, by writing a Lisp expression that yields t if so and nil if not.
Type M-: and use it to compute 234.
Get a list of keybindings by typing C-h b.
Look for two keybindings: C-h k and M-SPC. C-h k stands for “Type Control-h, then ‘k’.” M-SPC is “Meta Space”; on good keyboards you can get this by holding down Alt while hitting the space bar, but you may need to type “Esc” and then follow by hiting the space bar. We will examine these two keybindings in more detail.
Type C-h k C-h k and describes what happens and why. (This should relate to the C-h b output mentioned previously.)
Type C-h k M-SPC and describes what happens and why. (This should also relate.)
Try out M-SPC on some sample text, to see how it works.
Visit the source code for the function that implements M-SPC, by going to its help and clicking (or typing RET) on its source file name.
Notice how M-SPC is implemented in terms of a more-general function, which does not have a keybinding. Use M-: to execute this more-general function on a buffer, such that the function changes the buffer's contents.
Similarly, use M-x to execute the more-general function on a buffer.
Use the Emacs command M-x what-line and see what it does.
M-x what-line simply tells you what line you are on, not how many lines are in the buffer. Design and implement a command M-x which-line that acts like M-x what-line except that it says "Line 27 of 106" in contexts where M-x what-line would merely say "Line 27". Do this by using C-h f to get help about what-line, navigating through that help to find its source code, putting a copy of the source code into a new file which-line.el, editing that file, loading it into Emacs, and then executing your new command.
When counting all the lines in a buffer, simply count the number of newline characters that it contains. This means that if a buffer does not end in a newline, you should not count the characters after the last newline to be part of another line. In particular, an empty buffer has zero lines.
Consider the old-fashioned Python 2 script
randline.py.
What happens when this script is invoked on an empty file like
/dev/null, and why?
What happens when this script is invoked with Python 3 rather
than Python 2, and why? (You can run Python 3 on the SEASnet hosts by
using the command python3 instead
of python.)
Use Emacs to write a new script shuf.py in the style
of randline.py but using Python 3 instead.
Your script should implement the GNU
shuf
command that is part of GNU Coreutils.
GNU shuf is written in C, whereas
you want a Python implementation so that you can more easily add
new features to it.
Your program should support the following shuf
options, with the same behavior as GNU shuf:
--echo (-e),
--input-range (-i),
--head-count (-n),
--repeat (-r),
and --help.
As with GNU shuf, if --repeat (-r)
is used without --head-count (-n),
your program should run forever.
Your program should also support
zero non-option arguments or
a single non-option argument "-"
(either of which means read from standard input),
or a single non-option argument other than "-"
(which specifies the input file name).
Your program need not support the other options of GNU shuf.
As with GNU shuf, your program
should report an error if given invalid arguments.
Your solution should use the argparse module
instead of the obsolescent optparse.
It should not import any
modules other than argparse,
string and the non-optparse
modules that randline.py already imports.
Don't forget to change its usage message to
accurately describe the modified behavior.
What happens when your shuf.py script is invoked with Python 2 rather than Python 3, and why?
Submit the following files within a compressed tarball named assign2.tgz.
All files other than the .drib files should use GNU/Linux style, i.e., UTF-8 encoding with LF-terminated lines.
The shell command:
tar -tvf assign2.tgz
should output a list of file names that contains which-line.el etc., with sizes and other metainformation about the files.