String > Integer Conversion Problem


#1

Retro thanks to all who helped me with my last post. I’m certainly more
comfortable with Ruby now than then, but still a newbie as the following
will surely demonstrate.

Below, you can see that I’m checking command-line arguments to the
program for various conditions. Unfortunately, because the args are
stored as strings, when I convert them via to_i, empty and non-numerical
strings become 0. 0 is an acceptable element in this program, therefore
I can’t use it to test for invalid input. I’ve worked around this (sort
of), by creating two sets of variables for the arguments (one set as
strings, one set as integers). Unfortunately, this complicates the
code, and more importantly, leaves me stumped concerning how to test for
non-numeric values.

So, the program does what I want, except when the args are non-numeric
strings, and the code seems uglier than it ought to be.

Thanks in advance,

-ELf

def gen_chart(max)
x=0
y=0
local_chart = Array.new
while x<=max
y+=x
local_chart[x]=y
x+=1
end
local_chart
end

arg0 = ARGV[0]
arg1 = ARGV[1]

arg0i = ARGV[0].to_i
arg1i = ARGV[1].to_i

if arg0.nil? or (arg0i < 0) or (arg1i < 0)
#print usage
print <<-EOS

No args, or bad args!

Usage: #$0 [maxvalue]
#$0 [minvalue] [maxvalue]
EOS
elsif arg1.nil?
#do chart to arg0, print last pair
chart = gen_chart(arg0i)
puts arg0i.to_s + ": " + chart[arg0i].to_s
else
#do chart to arg1, print pairs from arg0 to last
chart = gen_chart(arg1i)
x=arg0i
y=arg1i
while x<=y
puts x.to_s + ": " + chart[x].to_s
x+=1
end
end


#2

On Dec 21, 2005, at 4:39 PM, Matthew F. wrote:

Below, you can see that I’m checking command-line arguments to the
program for various conditions.

See if this gives you some ideas:

if ARGV.all? { |n| n =~ /\A\d+\Z/ }
puts “Usage…”
exit
else
one, two = ARGV.map { |n| Integer(n) }
end

Hope that helps.

James Edward G. II


#3

On 12/21/05, Matthew F. removed_email_address@domain.invalid wrote:

strings, one set as integers). Unfortunately, this complicates the
def gen_chart(max)

No args, or bad args!
chart = gen_chart(arg1i)
x=arg0i
y=arg1i
while x<=y
puts x.to_s + ": " + chart[x].to_s
x+=1
end
end

Maybe this will give you an idea or two:

require ‘test/unit’

def process_command_line_arguments args
results = []
args.each do |arg|
raise “Hey, ‘#{ arg }’ needs to be a number” if !arg.match(/^\d*$/)
arg = arg.to_i
results << arg
end
results
end

class TestThis < Test::Unit::TestCase
def test_command_line_processing
assert_equal [2], process_command_line_arguments([“2”])
assert_equal [2, 3], process_command_line_arguments([“2”, “3”])
assert_raise(RuntimeError) { process_command_line_arguments(["-1"])
}
assert_raise(RuntimeError) { process_command_line_arguments([“1”,
“oog”]) }
assert_raise(RuntimeError) { process_command_line_arguments([“boo”,
“oog”])}
end
end

$ ruby a.rb
Loaded suite a
Started
.
Finished in 0.001163 seconds.

1 tests, 5 assertions, 0 failures, 0 errors


#4

On 12/21/05, Joe Van D. removed_email_address@domain.invalid wrote:

of), by creating two sets of variables for the arguments (one set as

end

#do chart to arg1, print pairs from arg0 to last

end

$ ruby a.rb
Loaded suite a
Started
.
Finished in 0.001163 seconds.

1 tests, 5 assertions, 0 failures, 0 errors

Whoops, this is probably better:

def process_command_line_arguments args
args.map do |arg|
raise “Hey, ‘#{ arg }’ needs to be a number” if !arg.match(/^\d*$/)
arg.to_i
end
end

Passes all the tests.


#5

Matthew F. wrote:

strings, one set as integers). Unfortunately, this complicates the
code, and more importantly, leaves me stumped concerning how to test for
non-numeric values.

The Integer() method raises ArgumentError if given an empty,
non-numeric, or otherwise non-well-formed string.


#6

On 12/21/05, James Edward G. II removed_email_address@domain.invalid wrote:

else
one, two = ARGV.map { |n| Integer(n) }
end

Neat, didn’t know about Enumerable#all? or about Integer().


#7

On 12/21/05, Timothy H. removed_email_address@domain.invalid wrote:

The Integer() method raises ArgumentError if given an empty,
non-numeric, or otherwise non-well-formed string.

On 12/21/05, James Edward G. II removed_email_address@domain.invalid wrote:

if ARGV.all? { |n| n =~ /\A\d+\Z/ }
puts “Usage…”
exit
else
one, two = ARGV.map { |n| Integer(n) }
end

So could we rewrite this as:

begin
one, two = ARGV.map{ |n| Integer(n) }
rescue ArgumentError
puts Usage
exit
end

?

Jacob F.


#8

Hi –

On Thu, 22 Dec 2005, Matthew F. wrote:

strings, one set as integers). Unfortunately, this complicates the
code, and more importantly, leaves me stumped concerning how to test for
non-numeric values.

So, the program does what I want, except when the args are non-numeric
strings, and the code seems uglier than it ought to be.

In addition to the other suggestions, you might find scanf useful:

require ‘scanf’
arg0, arg1 = ARGV.join.scanf("%d%d")

or something like that.

David


David A. Black
removed_email_address@domain.invalid

“Ruby for Rails”, from Manning Publications, coming April 2006!


#9

Jacob F. wrote:

begin
one, two = ARGV.map{ |n| Integer(n) }
rescue ArgumentError
puts Usage
exit
end

When the arguments to Integer are strings from the command line, yes. In
the general case Integer() can raise TypeError as well as ArgumentError,
for arguments like Integer([1,2])


#10

On Thu, 22 Dec 2005 00:21:39 -0000, removed_email_address@domain.invalid wrote:

In addition to the other suggestions, you might find scanf useful:

Me too. I’m definitely getting tunnel vision on the core doc, and
ignoring
the standard library a bit. Thanks for another good lead :slight_smile:


#11

On Dec 21, 2005, at 6:13 PM, Jacob F. wrote:

end

So could we rewrite this as:

begin
one, two = ARGV.map{ |n| Integer(n) }
rescue ArgumentError
puts Usage
exit
end

Yeah, that’s better. Neither of our versions checks the number of
arguments though and we probably should…

James Edward G. II


#12

On Dec 21, 2005, at 11:20 PM, James Edward G. II wrote:

one, two = ARGV.map{ |n| Integer(n) }

Excuse my ruby “newb-ness”, but what does this line actually do?
Mainly, what’s throwing me off is the “one, two” assignment (or
whatever it is).


#13

On 12/21/05, Timothy H. removed_email_address@domain.invalid wrote:

for arguments like Integer([1,2])
True, but I was referring specifically to the command line; vis the
OP’s question, and evidenced by my use of ARGV. :slight_smile:

Jacob F.


#14

On Wednesday 21 December 2005 22:26, J. Ryan S. wrote:

On Dec 21, 2005, at 11:20 PM, James Edward G. II wrote:

one, two = ARGV.map{ |n| Integer(n) }

Excuse my ruby “newb-ness”, but what does this line actually do?
Mainly, what’s throwing me off is the “one, two” assignment (or
whatever it is).

Try:

irb(main):001:0> one, two = 3, 4
=> [3, 4]
irb(main):002:0> one
=> 3
irb(main):003:0> two
=> 4

It’s a multiple assignment. It takes multiple values (or an array) and
spits
them into what’s on the left.

Map simply iterates through an array and runs the block (the thing in
braces)
each item, storing the result.

Thus, we’re converting everything in the ARGV array to an integer and
stuffing
it into two variables. The reason everyone else was saying it would be
a
good idea to check the length is the following:

irb(main):004:0> one, two = 3, 4, 5
=> [3, 4, 5]
irb(main):005:0> one
=> 3
irb(main):006:0> two
=> 4

Kinda bad to have mysteriously disappearing command line arguments. :slight_smile:
Play
around with it and I’m sure you’ll get the hang of it. Oh, and welcome
to
Ruby! :smiley:


#15

On Thu, 22 Dec 2005 04:20:04 -0000, James Edward G. II
removed_email_address@domain.invalid wrote:

else
end

Yeah, that’s better. Neither of our versions checks the number of
arguments though and we probably should…

I’m just wondering, in Java it’s a bit of a no-no using exceptions like
this (since they’re pretty heavy to put together). Is it the case in
Ruby?
And does that regexp match balance it out anyway?


#16

I see really two things happening here, string->int conversions and
command line parsing. Once you have the conversions understood (a good
thing to know) consider exploring more stuff in the packages.

Let me point you to OptionParser and GetOptLong. They both provide some
very useful command line parsing capabilities. It takes a little
experimentation to really understand what’s happening but well worth it
in my opinion.

-dwh-


#17

I disagree that this particular use of an exception would be a no-no in
Java. Inability to parse input is justifiably an “exceptional” case.
And the handling of that exceptional case is also appropriate.

The big “no-no” about exception usage is true for any language: “Don’t
use exceptions for flow control”.

The following code is “wrong” for various reasons as well as violating
the “axiom” above:

begin

display 1 through 10

i = 0
while true
unless i > 10
puts i
else
raise “End o’ the line”
end
i += 1
end
rescue
end

Ruby provides enough mechanisms for “controlling the flow” that using
exceptions for “normal” conditions is definitely poor style, if not
worse.

BTW “continuations” (related to exceptions) are a fairly powerful tool
to handle the times when strange flow control might be needed.


#18

On Thu, 22 Dec 2005 14:07:03 -0000, jwesley removed_email_address@domain.invalid
wrote:

I disagree that this particular use of an exception would be a no-no in
Java. Inability to parse input is justifiably an “exceptional” case.
And the handling of that exceptional case is also appropriate.

Agreed, I was referring more to the idea of swapping out flow control
for
exceptions in general. Obviously if the input is an exceptional case,
throw an exception. I have just been wondering about a few examples of
this I’ve seen in Ruby code, and just picked this as an ‘in’ to ask
about
it :wink:

unless i > 10

exceptions for “normal” conditions is definitely poor style, if not
worse.

Okay, good. That was my feeling too.

BTW “continuations” (related to exceptions) are a fairly powerful tool
to handle the times when strange flow control might be needed.

I can’t wait to find something I can try continuations out on, though I
remember reading somewhere that they too are slow, so one to keep for
those strange cases as you say?

Cheers,


#19

Hi –

On Thu, 22 Dec 2005, Ross B. wrote:

seen in Ruby code, and just picked this as an ‘in’ to ask about it :wink:

while true
Ruby provides enough mechanisms for “controlling the flow” that using
exceptions for “normal” conditions is definitely poor style, if not
worse.

Okay, good. That was my feeling too.

I agree in general, although… there’s one case where I can’t resist,
at least sometimes, and that’s this:

if obj.respond_to(“meth”)
obj.meth
else

end

I really dislike the repetition there, and it also technically isn’t
thread-safe:

a = Object.new
def a.x; end

Thread.new do
sleep 1
class << a; undef_method(“x”); end
end

if a.respond_to?(“x”)
sleep 2
a.x
end

=> undefined method `x’ for #Object:0x1cd508 (NoMethodError)

I don’t know any way around it, though, except:

begin
obj.meth
rescue NoMethodError

end

or some variant thereof. (Obviously in true duck-typing cases you
just send the message without this kind of check, but there are cases
where the check makes sense.)

I’ve toyed with the idea of some kind of special “nack” object that
would be returned on these kinds of method calls, but I don’t think it
plays well with method_missing.

David


David A. Black
removed_email_address@domain.invalid

“Ruby for Rails”, from Manning Publications, coming April 2006!


#20

removed_email_address@domain.invalid wrote:

The following code is “wrong” for various reasons as well as violating
end
Okay, good. That was my feeling too.

obj.meth
rescue NoMethodError

end

This has the unfortunate side effect of conflating NoMethodErrors that
are reported for other method calls besides the original obj.meth but
which occur during that method. What’s the best way of handling that?
Compare exception.backtrace depth with the current backtrace depth?

It’s not really threadsafe either. By the time is
executed, #meth could have been defined (though you do know it was
undefined at the time of the method call, which is an improvement over
the #respond_to version).