I have the following code:
address = "#{(article/"div.address").inner_html.strip_html.squish}"
(using Hpricot)
And in some instances...
address = "#{(article/"div.address").inner_html.strip_html.squish}"
...is nil
I would like the script to keep chugging along, possibly replacing nil with an empty string.
Any tips?
Edit
I have traced the problem better to:
puts "#{link[0].to_s}\n" unless link.empty?
(.backtrace points to this particular line in the source.)
So the revised question is: why doesn't that line just not get parsed? Why does it throw an error? I thought that using unless will just skip it...
Use :to_s method:
nil.to_s == ''
Is try what you are looking for? http://api.rubyonrails.org/classes/Object.html#method-i-try
Thank you all for the support and helpful tips, in the end it was a matter of using the proper method, I ended up solving my problem by using:
unless uri.query.nil?
But I did come to make use of both .to_s and try in my source, and I wish I could pick two answers as the right one!
Related
I'd like to do this:
summary << reason
In my case, summary is a string, containing several sentences, and reason is one such sentence.
This works fine if the target already has a value, but sometimes summary can be nil. In that case, this raises:
NoMethodError: undefined method `<<' for nil:NilClass
So, I could write something like this:
if summary
summary << reason
else
summary = reason
end
This is cumbersome and ugly. I can hide it away in a new method like append(summary, reason), but I'm hoping there's a ruby idiom that can wrap this up concisely.
I've optimistically tried a few variants, without success:
summary += reason
summary &<< reason
In other scenarios, I might build an array of reasons (you can shovel into an empty array just fine), then finally join them into a summary...but that's not viable in my current project.
I also can't seed summary with an empty string (shoveling into an empty string also works fine), as other code depends on it being nil at times.
So, is there a "safe shovel" or simple "shovel or assign" idiom in Ruby, particularly for strings that might be nil?
I prefer #Oto Brglez's answer, but it inspired another solution that might be useful to someone:
summary = [summary, reason].join
This may or may not be easier to read, and probably is less performant. But it handles the nil summary problem without explicit alternation.
You can solve this with something like this; with the help of ||.
summary = (summary || '') + reason
Or like so with the help of ||= and <<:
(summary ||= '') << reason
I am attempting to modify someone's script.
I have managed to modify everything but there is one problem left I am unable to solve:
disp_status("\tAnswer: #{convert_err(results["status"])}")
This produces various outputs as it is run, however, when the output is "ERROR", I want it to do an action. I am not sure how to limit it to "Error", as it appears to always run the method no matter the output.
What I tried was:
if #{convert_err(results["status"])} =~ /ERROR/
and a lot of similar iterations without any luck. Can anyone help?
In ruby interpolation doesn't work without double-quotes. But using interpolation here is an over kill, so just change the line in question from:
if #{convert_err(results["status"])} =~ /ERROR/
To
if convert_err(results["status"]) =~ /ERROR/
And should it should work! :-)
I think the .include? method might be helpful. You could do:
if "#{convert_err(results["status"])}".include?("ERROR")
Furthermore if convert_err returns a string you could just call:
if convert_err(results["status"]).include?("ERROR")
And another option would be to call .to_s which will convert the result of convert_err to a string. So that would look like:
if convert_err(results["status"]).to_s.include?("ERROR")
For further reference read: http://www.ruby-doc.org/core-2.1.4/String.html#method-i-include-3F
I have to use String.scan function, which returns empty array if there is no match.
I wanted to assign a variable with the scan function and check it there is a match, but unfortunately I cannot do that because it won't return nil or false on no match.
I wanted to do this (1 line):
if ip = str.scan(/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/)
...
#use ip
end
but because it won't return nil on no match I must do:
ip_match = str.scan(/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/)
unless ip_match.empty?
#use ip
end
Is there some more elegant way to write this - to be able to do assignment and empty check at the same time or some other way to beautify the code?
Thanks
Since scan returns an array, and even if you are sure there would be only one result, you could do this.
str.scan(/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/).each do |ip|
#use ip
end
There's a difference between elegant and cryptic or "concise".
In Perl you'll often see people write something equivalent to:
if (!(ip = str.scan(/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/)).empty?)
It's a bit more concise, terse, tight, whatever you want to call it. It also leads to maintenance issues because of the = (equate) vs. what should normally be an equality test. If the code is passed to someone who doesn't understand the logic, they might mistakenly "correct" that, and then break the code.
In Ruby it's idiomatic to not use equate in a conditional test, because of the maintenance issue, and instead use the assignment followed by a test. It's clearer code.
Personally, I prefer to not use unless in that sort of situation. It's an ongoing discussion whether unless helps generate more understandable code; I prefer if (!ip_match.empty?) because it reads more like we'd normally talk -- I seldom start a statement with unless in conversation. Your mileage might vary.
I would preferably do something like this using String helper match
ip_validator = /^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/
# match return nil if no match
if str.match ip_validator
# blah blah blah.....
end
help me keep code dry and clean.
May be this is not the most elegant , looking for others if any :)
Your ip_validator regex seems to be week check this out Rails 3: Validate IP String
Not sure if this is possible but can I call a method from an irb shell with spaces between parameters rather than commas (don't ask) ? Lets say I have a method
def start_band(member1, member2, member3, member4)
#do something
end
And then I call it like the following:
irb>> start_band "John" "Paul" "George" "Ringo"
EDIT: Would it be possible to detect every keypress instead?
No, you can't do that. Not with strings anyway.
No.
You could use something like treetop to write a really simple DSL, or just play monkey-parsing games, but that won't solve your exact question.
The other obvious answer is this, which also fails:
irb>> start_band %W(John Paul George Ringo)
Creating an irb-like CLI isn't difficult, and may be adequate, depending on what your actual requirements are.
There is actually a very easy way to get rid of the commas. You can even get rid of the quotes, too:
def start_band(members)
#members is an array
end
start_band %w(John Paul George Ringo)
The limitation is that you can't use spaces inside your strings, and you still need start-end terminations (can use other characters instead of parenthesis though).
Durr! I really approached this the wrong way. I simply needed to run
#members = gets
to allow the input as required. Thanks for the responses nonetheless.
A Ruby dev I know asked this; my answer is below... Are there other, better reasons?
Why do so many Ruby programmers do
"#{string}"
rather than
string
since the second form is simpler and more efficient?
Is this a common idiom for Ruby developers? I don't see it that much.
Smaller changes when you later need to do more than simply get the value of the string, but also prepend/append to it at the point of use seems to be the best motivation I can find for that idiom.
There is only one case where this is a recommended idiom :
fname = 'john'
lname = 'doe'
name = "#{fname} #{lname}"
The code above is more efficient than :
name = fname + ' ' + lname
or
name = [fname, lname].join(' ')
What's the broader context of some of the usages? The only thing I can come up with beyond what's already been mentioned is as a loose attempt at type safety; that is, you may receive anything as an argument, and this could ensure that whatever you pass in walks like a duck..or, well, a string (though string.to_s would arguably be clearer).
In general though, this is probably a code smell that someone along the way thought was Best Practices.
I use this kind of code, so that I can pass nil as string and it still will work on a string, rather than seeing some exceptions flying:
def short(string = nil)
"#{string}"[0..7]
end
And it's easier/faster to append some debug code, if it's already in quotes.
So in short: It's more convenient.
Interesting answers, everyone. I'm the developer who asked the original question. To give some more context, I see this occasionally at my current job, and also sometimes in sample code on the Rails list, with variables that are known in advance to contain strings. I could sort of understand it as a substitute for to_s, but I don't think that's what's going on here; I think people just forget that you don't need the interpolation syntax if you're just passing a string variable.
If anyone tried to tell me this was a best practice, I'd run away at top speed.
maybe it is easy way to convert any to string? Because it is the same as call to_s method. But it is quite strange way :).
a = [1,2,3]
"#{a}"
#=> "123"
a.to_s
#=> "123"
I could image this being useful in cases where the object being interpolated is not always a String, as the interpolation implicitly calls #to_s:
"#{'bla'}" => "bla"
"#{%r([a-z])}" => "(?-mix:[a-z])"
"#{{:bla => :blub}}" => "blablub"
May make sense when logging something, where you don't care so much about the output format, but never want an error because of a wrong argument type.