p vs. print

[Abder-Rahman Ali]

I wrote the following scripts from section (2) here:
http://ruby.gfd-dennou.org/tutorial/gokuraku/index-e.html

require "rubygems" # Not in the example
require "narray"
ary1 = NArray.sfloat(3,4)

When I tried to display the result using

print ary1

It did NOT show anything.

While when I used:

p ary1

I got the result displayed?

Why is that?

Thanks.

 

[Alex Stahl]

Ruby uses "puts", not "print". "p" is short for "puts".

Try this:

puts ary1

You'll get the same results as:

p ary1

 

[Quintus]

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Am 02.09.2010 21:23, schrieb Alex Stahl:

Ruby uses "puts", not "print". "p" is short for "puts".

Try this:

puts ary1

You'll get the same results as:

p ary1

This is definitely wrong. #p is quite another method than #puts and yet
another than #print. Look at this:

irb(main):001:0> puts [1, 2, 3]
1
2
3
=> nil
irb(main):002:0> p [1, 2, 3]
[1, 2, 3]
=> [1, 2, 3]
irb(main):003:0> print [1, 2, 3]
[1, 2, 3]=> nil
irb(main):004:0>

Vale,
Marvin
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[Andrew Wagner]

[Note: parts of this message were removed to make it a legal post.]

Actually, "p x" is equivalent to "puts x.inspect", not "puts x"

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Am 02.09.2010 21:23, schrieb Alex Stahl:

Ruby uses "puts", not "print". "p" is short for "puts".

Try this:

puts ary1

You'll get the same results as:

p ary1

This is definitely wrong. #p is quite another method than #puts and yet
another than #print. Look at this:

irb(main):001:0> puts [1, 2, 3]
1
2
3
=> nil
irb(main):002:0> p [1, 2, 3]
[1, 2, 3]
=> [1, 2, 3]
irb(main):003:0> print [1, 2, 3]
[1, 2, 3]=> nil
irb(main):004:0>

Vale,
Marvin
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[Colin Bartlett]

[Note: parts of this message were removed to make it a legal post.]

Am 02.09.2010 21:23, schrieb Alex Stahl:

This is definitely wrong. #p is quite another method than #puts and yet

another than #print. Look at this ...

And as another example of the differences:
class P
def inspect(); "P#inspect"; end
def to_s(); "P#to_s"; end
end

q = P.new
puts "p"
p q #=> "P#inspect"
puts "puts"
puts q #=> "P#to_s"
puts "print"
print q
puts ":: just after print"
#=> "P#to_s:: just after print"

 

[Abder-Rahman Ali]

Ruby uses "puts", not "print". "p" is short for "puts".

Try this:

puts ary1

You'll get the same results as:

p ary1

Thanks Alex. Actually, if I use:

puts ary1

I do NOT get an output (Empty).

 

[Abder-Rahman Ali]

What is "inspect"? What does it do?

 

[Andrew Wagner]

[Note: parts of this message were removed to make it a legal post.]

It just returns a user-friendly version of the object. It can be overridden
to do whatever you want, it's just a regular ol' method on Object.

 

[Alex Stahl]

Sorry, my wording was off. Understood that they're different methods.

I think of them synonymously, and so when I say "short for", I mean
that's my way of thinking about how they accomplish similar tasks, not
that "p" is literally a representation of "puts".

Thanks for the clarification in any case.

 

[Andrew Wagner]

[Note: parts of this message were removed to make it a legal post.]

No problem. I actually used to think that they were identical, which led to
some confusion. That's the only reason i point it out.

 

[Abder-Rahman Ali]

Thanks everyone for the clarification.

@Andrew. When you say: "...it's just a regular ol' method on Object.".

What do you mean by "ol'"?

Thanks.

 

[Mark T]

Not to mention pp which is prettyprint
http://ruby-doc.org/stdlib/libdoc/pp/rdoc/index.html
And there is ap which is awesomeprint http://github.com/michaeldv/awesome_p=
rint

MarkT

--=20
(+61 4) 0679 5734 :: skype: govirtual.com.au :: =E3=83=81=E3=82=A7=E3=83=83=
=E3=82=AF=E3=82=A2=E3=82=A6=E3=83=88=E3=81=8C=E3=80=81Jingle =E3=81=A0!
::It's a Jingle Out There!

 

[Brian Candler]

When I tried to display the result using

print ary1

It did NOT show anything.

print(x) calls x.to_s to get the string representation, then sends that
to $stdout.

It looks like the object you have returns an empty string or nil from
its to_s method (which is odd, but you'd have to talk to the author of
the NArray class about that)

puts(x) is like print(x), but adds a newline if there isn't one at the
end of the string already.

p(x) is like puts(x.inspect), where x converts an object into a
debugging string form, that is, one which shows its internal state.

Try this program to see the differences:

class Foo
def initialize(a)
@a = a
end
def to_s
"here's a string"
end
end

f = Foo.new(123)
print f
puts f
p f

 

[Edmond Kachale]

Let IRB speak for himself:
****

x = [2,4,1] => [2, 4, 1]
p x

[2, 4, 1]
=> nil2
4
1
=> nil"[2, 4, 1]"
=> nil[2, 4, 1]
=> nil

print x.inspect [2, 4, 1]=> nil
p x.to_s

"241"
=> nil241
=> nil241=> nil
****

p x = puts x.inspect

ceekays
=======

 

[Abder-Rahman Ali]

@Brian.

Thanks for your reply. That makes it more clear.

This is the output I got from running your script:


C:\Users\Abder-Rahman\Desktop\Research>ruby p_vs_print_vs_puts.rb
here's a stringhere's a string
#<Foo:0x2c25930 @a=123>

Can you just describe this part: #<Foo:0x2c25930 @a=123>

And, when you said: "p(x) is like puts(x.inspect), [[where x converts an
object]] into a debugging string form, that is, one which shows its
internal state."

Shouldn't "... where x converts an object...]], be "... where "inspect"
converts an object..."?

Thanks.

 

[Abder-Rahman Ali]

Thanks @Edmond for the clarification.

 

[Abder-Rahman Ali]

Not to mention pp which is prettyprint
http://ruby-doc.org/stdlib/libdoc/pp/rdoc/index.html
And there is ap which is awesomeprint
http://github.com/michaeldv/awesome_print

MarkT

That's nice.

 

[Abder-Rahman Ali]

Thanks @Savard.

 

[Brian Candler]

This is the output I got from running your script:


C:\Users\Abder-Rahman\Desktop\Research>ruby p_vs_print_vs_puts.rb
here's a stringhere's a string
#<Foo:0x2c25930 @a=123>

Can you just describe this part: #<Foo:0x2c25930 @a=123>

That's what Object#inspect returns: a string containing the class name,
the pointer to the object instance in memory, and the values of all
instance variables. Other classes inherit this from Object, although
they can override it if they wish.

And, when you said: "p(x) is like puts(x.inspect), [[where x converts an
object]] into a debugging string form, that is, one which shows its
internal state."

Shouldn't "... where x converts an object...]], be "... where "inspect"
converts an object..."?

Yes, my mistake.

 

[Abder-Rahman Ali]

Thanks @Brian for this nice clarification.

You mean here (inspect) right?

"Other classes inherit this from Object, although they can override it
if they wish."