Re: [Courses] [Ruby] Lesson 0: Installing, References, and your first homework assignment

[Renata Vidal]

Hi!

I just deleted the Joe's mail, but I would like to know what means the command "a,b="

I will introduce myself soon, because I didnt my homework yet.

Thanks,

Renata
De:courses-bounces at linuxchix.org

Para:courses at linuxchix.org

Cópia:

Data:Wed, 9 Nov 2005 12:12:21 -0800

Assunto:Re: [Courses] [Ruby] Lesson 0: Installing, References, and your first homework assignment

> Hi! Laurel, thanks for running the course.
> 
> I'm a longtime programmer in lots of languages. My two favorites
> are C and Python; I suppose because they're simple, compact and
> efficient. I've used Ruby and Rails a little bit, but I want to
> learn more about Ruby because although I can get by in it, I
> don't feel like I understand it as well as I'd like to.
> 
> I expect most of my Ruby use will be for Rails, but who knows?
> Maybe the course will convince me that I should use it instead of
> Python for writing standalone scripts. And every language has
> strengths and weaknesses, so even if I don't switch to Ruby as
> my main scripting language, I'm sure there will be times when it's
> the best tool for the job.
> 
> Laurel Fan writes:
> > Any modern Linux distribution has ruby package(s). It might even
> > already be installed. (To check, try 'ruby --version' in a shell). If
> 
> I'm currently running Ubuntu "Hoary Hedgehog". Although it offers
> Ruby packages (which are probably fine for this course), I didn't
> have much luck getting Rails and Gems to work, even after adding the
> backports from Breezy. Also, the built-in Ruby didn't install a
> "ruby" command so I had to make a symlink (I notice someone else
> just asked about that on newchix recently).
> 
> I ended up building Ruby and Gems from source, then using gems to
> install Rails. That worked fine and I've had no problem with the
> setup. I suspect this all works out of the box on Breezy.
> 
> For my homework assignment, I rewrote in Ruby a little program that
> I wrote last week for spam filtering. I suddenly started getting a
> lot more spam with unprintable characters in the subject, so I
> wanted a program to calculate how many characters in a set of
> strings was printable vs. unprintable. I tried at first to write it
> in Python, but it turned out Python doesn't have any easy way to do
> the equivalent of C's "isprint" test. Eventually I gave up and wrote
> it in C, which was really easy.
> 
> Googling, it turns out Ruby doesn't have a way to do isprint()
> either. :-( But I did find a way to delete all unprintable characters
> from a string, so I wrote it using that. (I think Python has that too,
> so I could probably go back and write it in Python the same way.)
> 
> #!/usr/local/bin/ruby
> 
> # This program checks its runtime arguments for number of
> # printable and unprintable characters.
> 
> class SmartString < String
> def print_unprint()
> toprint = self.gsub(/[^[:print:]]/, '')
> return [toprint.length, self.length - toprint.length]
> end
> end
> 
> # main: loop over each input word
> 
> total_printable = 0
> total_unprintable = 0
> ARGV.each do |word|
> p_u = SmartString.new(word).print_unprint()
> total_printable += p_u[0]
> total_unprintable += p_u[1]
> end
> 
> print "Total: ", total_printable, " printable, ",
> total_unprintable, " unprintable\n"
> 
> You said to analyze part of the code, so I'll analyze the class
> SmartString. I made it a new class that inherits from the normal
> String class, so that I could use all the built-in string methods.
> Eventually I'd probably want to add some other tests (e.g. checking
> how much punctuation and numbers there is compared to letters, maybe
> checking word length) but right now the only new method is a
> function called print_unprint that returns an array of two items:
> the number of printable characters in the string, and the number of
> unprintable characters.
> 
> It does that by replacing (using gsub, which does a global
> substitution over the string) any unprintable character in the string
> with '' (i.e. deleting it). It turns out Ruby has a character class
> called [:print:] (the character classes are listed on p. 72 of the
> second edition of Programming Ruby) so [^[:print:]] matches any
> character that's not printable. (I found that snippet by googling.
> There are lots of useful Ruby snippets on the web if you google for
> terms related to what you're trying to do.)
> 
> I confess I'm not 100% clear on the two sets of brackets: the outside
> set says "for this regular expression, use any character in this
> group" and I grok that, but the inner set with the colons, [::],
> seems to be something you always put around character classes
> but I'm not comfortable enough yet with the syntax to be sure why.
> 
> The return in print_unprint uses [ ] to build up a two-element array
> on the fly, so it can return both the printable and unprintable counts.
> Then the caller can index the printable count with [0] and the
> unprintable count with [1]. If I were actually using this for a
> spam filter, instead of printing the count I'd exit with a nonzero
> status if there were too many unprintables.
> 
> ...Akkana
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