`(?i)` starts case-insensitive mode

`(?-i)` turns off case-insensitive mode

More information at the [&quot;Turning Modes On and Off for Only Part of The Regular Expression&quot; section of this page][1]: 

&gt; Modern regex flavors allow you to apply modifiers to only part of the
&gt; regular expression. If you insert the modifier (?ism) in the middle of
&gt; the regex, the modifier only applies to the part of the regex to the
&gt; right of the modifier. You can turn off modes by preceding them with a
&gt; minus sign. All modes after the minus sign will be turned off. E.g.
&gt; (?i-sm) turns on case insensitivity, and turns off both single-line
&gt; mode and multi-line mode.
&gt; 
&gt; Not all regex flavors support this. JavaScript and Python apply all
&gt; mode modifiers to the entire regular expression. They don&#39;t support
&gt; the (?-ismx) syntax, since turning off an option is pointless when
&gt; mode modifiers apply to the whole regular expressions. All options are
&gt; off by default.
&gt; 
&gt; You can quickly test how the regex flavor you&#39;re using handles mode
&gt; modifiers. The regex (?i)te(?-i)st should match test and TEst, but not
&gt; teST or TEST.


  [1]: http://www.regular-expressions.info/modifiers.html

`(?i)` turns on _case-insensitive_ mode, `(?-i)` turns it off.

For example, if you tried `(?i)te(?-i)st`, it would match __test__, __TEst__, __tEst__, but not __teST__.

Taken directly from ruby docs.

&gt; The end delimiter for a regexp can be followed by one or more
&gt; single-letter options which control how the pattern can match.
&gt; 
&gt;
&gt; /pat/i - Ignore case 
&gt;
&gt; /pat/m - Treat a newline as a character matched by . 
&gt;
&gt; /pat/x - Ignore whitespace and comments in the pattern 
&gt;
&gt; /pat/o -&gt; Perform #{} interpolation only once 
&gt;
&gt; i, m, and x can also be applied on
&gt; the subexpression level with the (?on-off) construct, which enables
&gt; options on, and disables options off for the expression enclosed by
&gt; the parentheses.

I have the following test code:

    void Button_Click(object sender, RoutedEventArgs e)
   	{
   		var source = new CancellationTokenSource();
    
   		var tsk1 = new Task(() =&gt; Thread1(source.Token), source.Token);
   		var tsk2 = new Task(() =&gt; Thread2(source.Token), source.Token);
    
		tsk1.Start();
		tsk2.Start();
    
		source.Cancel();
    
		try
		{
			Task.WaitAll(new[] {tsk1, tsk2});
		}
		catch (Exception ex)
		{
            // here exception is caught
		}
    }
    
  	void Thread1(CancellationToken token)
	{
		Thread.Sleep(2000);

        // If the following line is enabled, the result is the same.
        // token.ThrowIfCancellationRequested();
    }
    
	void Thread2(CancellationToken token)
	{
    	Thread.Sleep(3000);
    }

In the thread methods I don&#39;t throw any exceptions, but I get `TaskCanceledException` in `try-catch` block of the outer code which starts the tasks. Why this happens and what is the purpose of `token.ThrowIfCancellationRequested();` in this case. I believe the exception should only be thrown if I call `token.ThrowIfCancellationRequested();` in the thread method.

Why does TaskCanceledException occur?

My code is:

    import scriptlib.abc
    import scriptlib.xyz

    def foo():
      ... some operations


but the scriptlib is in some other directory, so I will have to include that directory in environment variable &quot;PYTHONPATH&quot;.

Is there anyway in which I can first add the scriptlib directory in environment variable &quot;PYTHONPATH&quot; before import statement getting executed like :

    import sys
    sys.path.append(&#39;/mypath/scriptlib&#39;)
    import scriptlib.abc
    import scriptlib.xyz

    def foo():
      ... some operations

If so, is the value only for that command prompt or is it global ?

Thanks in advance

set pythonpath before import statements

Could someone explain what `(?i)` and `(?-i)` wrapping a word in regex mean?

    (?i)test(?-i)

I tested and it matches `test`, `TEST`, and `teSt`. But I have never seen this before. What does the `?` before `i` mean? I saw this [here](https://github.com/dwilkie/carrierwave_direct/blob/master/lib/carrierwave_direct/uploader.rb#L85).


What do `?i` and `?-i` in regex mean?

Could someone explain what <code>(?i)</code> and <code>(?-i)</code> wrapping a word in regex mean?
<pre><code class="hljs language-scss">(?i)test(?-i)
</code></pre>
I tested and it matches <code>test</code>, <code>TEST</code>, and <code>teSt</code>. But I have never seen this before. What does the <code>?</code> before <code>i</code> mean? I saw this <a href="https://github.com/dwilkie/carrierwave_direct/blob/master/lib/carrierwave_direct/uploader.rb#L85" target="_blank" rel="noopener noreferrer">here</a>.

I can&#39;t get capybara working with rspec. It gives me this error:

    undefined method `visit&#39; for #&lt;RSpec::Core::ExampleGroup::Nested_1:0x16529f8 @example=nil&gt;

I know there are lots of posts about this but non of the solutions are working for me. Most of them involve the specs not being in /spec/features - which mine is in.

First the error:
&lt;!-- language-all: lang-rb --&gt;

    $bundle exec rspec spec
    F

    Failures:

      1) security signs users in
         Failure/Error: visit &quot;/sessions/new&quot;
         NoMethodError:
           undefined method `visit&#39; for #&lt;RSpec::Core::ExampleGroup::Nested_1:0x16529f8 @example=nil&gt;
         # ./spec/features/security_spec.rb:4:in `(root)&#39;
    
     Finished in 0.006 seconds
     1 example, 1 failure

    Failed examples:

    rspec ./spec/features/security_spec.rb:3 # security signs users in

I think its important to note that at first I was using the URL Helper &#39;new_sessions_path&#39; and it kept giving me an error `undefined local variable or method &#39;new_sessions_path&#39;`. I know it is valid because:
&lt;!-- language-all: lang-rb --&gt;

    $ rake routes
    logout_sessions GET    /sessions/logout(.:format) sessions#logout
           sessions POST   /sessions(.:format)        sessions#create
       new_sessions GET    /sessions/new(.:format)    sessions#new
          contracts POST   /contracts(.:format)       contracts#create
      new_contracts GET    /contracts/new(.:format)   contracts#new
     edit_contracts GET    /contracts/edit(.:format)  contracts#edit
                    GET    /contracts(.:format)       contracts#show
                    PUT    /contracts(.:format)       contracts#update
                    DELETE /contracts(.:format)       contracts#destroy
               root        /                          contracts#index

My Gemfile:
&lt;!-- language-all: lang-rb --&gt;

    source &#39;https://rubygems.org&#39;

    gem &#39;rails&#39;, &#39;3.2.11&#39;
    gem &#39;execjs&#39;

    group :assets do
      gem &#39;sass-rails&#39;,   &#39;~&gt; 3.2.3&#39;
      gem &#39;coffee-rails&#39;, &#39;~&gt; 3.2.1&#39;
      gem &#39;uglifier&#39;, &#39;&gt;= 1.0.3&#39;
    end

    gem &#39;jquery-rails&#39;
    gem &#39;activerecord-oracle_enhanced-adapter&#39;, &#39;~&gt; 1.4.1&#39;
    gem &#39;jruby-openssl&#39;
    gem &#39;therubyrhino&#39;
    gem &#39;kaminari&#39;
    gem &#39;nokogiri&#39;

    group :development do
      gem &#39;warbler&#39;
    end

    group :test do
      gem &#39;rspec-rails&#39;
      gem &#39;capybara&#39;
      gem &#39;activerecord-jdbcsqlite3-adapter&#39;
    end


spec_helper.rb inside of my_app/spec:
&lt;!-- language-all: lang-rb --&gt;

    # This file is copied to spec/ when you run &#39;rails generate rspec:install&#39;
    ENV[&quot;RAILS_ENV&quot;] ||= &#39;test&#39;
    require File.expand_path(&quot;../../config/environment&quot;, __FILE__)
    require &#39;rspec/rails&#39;
    require &#39;rspec/autorun&#39;

    # Capybara integration
    require &#39;capybara/rspec&#39;
    require &#39;capybara/rails&#39;

    # Requires supporting ruby files with custom matchers and macros, etc,
    # in spec/support/ and its subdirectories.
    Dir[Rails.root.join(&quot;spec/support/**/*.rb&quot;)].each {|f| require f}

    RSpec.configure do |config|
      # Remove this line if you&#39;re not using ActiveRecord or ActiveRecord fixtures
      # config.fixture_path = &quot;#{::Rails.root}/spec/fixtures&quot;
      config.use_transactional_fixtures = true
      config.infer_base_class_for_anonymous_controllers = false
      config.order = &quot;random&quot;
      # Include path helpers
      config.include Rails.application.routes.url_helpers
    end


my_app/spec/features/security_spec.rb:
&lt;!-- language-all: lang-rb --&gt;

    describe &quot;security&quot;, :type =&gt; :feature do
      it &quot;signs users in&quot; do
        visit &quot;/sessions/new&quot;
        fill_in &quot;username&quot;, :with =&gt; &quot;user&quot;
        fill_in &quot;password&quot;, :with =&gt; &quot;pass&quot;
        click_button &quot;Sign In&quot;

        page.should have_content(&#39;Login Successful&#39;)
      end
    end

I&#39;ve tried defining the test above both with and without `:type =&gt; :feature`. It makes no difference either way. Any ideas what I should try next?

undefined method `visit&#39; when using RSpec and Capybara in rails

I am following the rails tutorial videos and I can&#39;t figure out what the `db:test:prepare` command actually does. Can someone provide an explanation? 

What does rake db:test:prepare actually do?

[starting from Rails 4][1], everything would have to run in threaded environment by default. What this means is all of the code we write **AND** __ALL__ the gems we use are required to be `threadsafe`

so, I have few questions on this:

1. what is NOT thread-safe in ruby/rails? **Vs** What is thread-safe in ruby/rails?
2. Is there a list of gems that _is_ known to be threadsafe or vice-versa?
3. is there List of common patterns of code which are NOT threadsafe example `@result ||= some_method`?
4. Are the data structures in ruby lang core such as `Hash` etc threadsafe?
5. On MRI, where there a [`GVL`/`GIL`][2] which means only 1 ruby thread can run at a time except for `IO`, does the threadsafe change effect us? 


  [1]: http://edgeguides.rubyonrails.org/4_0_release_notes.html#railties-notable-changes
  [2]: http://en.wikipedia.org/wiki/Global_Interpreter_Lock

how to know what is NOT thread-safe in ruby?

In Ruby 2.0.0-p0, the `__dir__` variable was introduced for easy access to the directory of the file currently being executed.

Why is `__dir__` lowercase when `__FILE__` is uppercase?

Why is __FILE__ uppercase and __dir__ lowercase?

I&#39;m attempting to follow the Hartl Rails Tutorial, and having trouble with the bundler gem.

When using the commands &#39;bundle install&#39; or &#39;bundle update&#39; I get the following output: 

&gt; Fetching source index from https://rubygems.org/
&gt; 
&gt; Could not fetch specs from https://rubygems.org/

I&#39;ve searched for this output, but did not find many related issues online. 

Maybe I have another gem that is interrupting bundler? I have little experience with rails at this point.

        source &#39;https://rubygems.org&#39;
    
    gem &#39;rails&#39;, &#39;3.2.12&#39;
    
    group :development do
      gem &#39;sqlite3&#39;, &#39;1.3.5&#39;
    end
    
    
    # Gems used only for assets and not required
    # in production environments by default.
    group :assets do
      gem &#39;sass-rails&#39;,   &#39;3.2.5&#39;
      gem &#39;coffee-rails&#39;, &#39;3.2.2&#39;
    
      gem &#39;uglifier&#39;, &#39;1.2.3&#39;
    end
    
    gem &#39;jquery-rails&#39;, &#39;2.0.2&#39;


**The solution for me was two parts:** I changed https to http, and that temporarily solved the issue. The second issue was that I think I had a bad install of ruby 2.0.0 even though I was using a fresh install of ruby 1.9.3. So I reinstalled ruby 2.0.0, and I could use bundle install with https.

Bundle Install could not fetch specs from https://rubygems.org/

I can use this code below to create a new file with the substitution of `a` with `aa` using regular expressions.

    import re

    with open(&quot;notes.txt&quot;) as text:
        new_text = re.sub(&quot;a&quot;, &quot;aa&quot;, text.read())
        with open(&quot;notes2.txt&quot;, &quot;w&quot;) as result:
            result.write(new_text)

 I was wondering do I have to use this line, `new_text = re.sub(&quot;a&quot;, &quot;aa&quot;, text.read())`, multiple times but substitute the string for others letters that I want to change in order to change more than one letter in my text? 

That is, so `a`--&gt;`aa`,`b`--&gt; `bb` and `c`--&gt; `cc`. 

So I have to write that line for all the letters I want to change or is there an easier way. Perhaps to create a &quot;dictionary&quot; of translations. Should I put those letters into an array? I&#39;m not sure how to call on them if I do. 

How can I do multiple substitutions using regex?

One of the lines in my script contains a PHP closing tag inside a string. Under normal operation this does not cause a problem, but I need to comment out the line.

I have tried to comment out this line with `//`, `/*` `*/` and `#` but none of them work, the parser considers closing tag to be an actual closing tag.

Here is the line in question:

    $string = preg_replace(&#39;#&lt;br\s*/?&gt;(?:\s*&lt;br\s*/?&gt;)+#i&#39;, &#39;&lt;br /&gt;&#39;, $string);
    //                              ^^             ^^

What can I do to comment out the above line?


Convert PHP closing tag into comment

of course I could replace specific arguments like this:

        mydata=c(&quot;&#225;&quot;,&quot;&#233;&quot;,&quot;&#243;&quot;)
        mydata=gsub(&quot;&#225;&quot;,&quot;a&quot;,mydata)
        mydata=gsub(&quot;&#233;&quot;,&quot;e&quot;,mydata)
        mydata=gsub(&quot;&#243;&quot;,&quot;o&quot;,mydata)
        mydata

but surely there is a easier way to do this all in onle line, right?
I dont find the gsub help to be very comprehensive on this. 

Replace multiple letters with accents with gsub

I would like to cleanly filter a dataframe using regex on one of the columns.

For a contrived example:

    In [210]: foo = pd.DataFrame({&#39;a&#39; : [1,2,3,4], &#39;b&#39; : [&#39;hi&#39;, &#39;foo&#39;, &#39;fat&#39;, &#39;cat&#39;]})
    In [211]: foo
    Out[211]: 
       a    b
    0  1   hi
    1  2  foo
    2  3  fat
    3  4  cat

I want to filter the rows to those that start with `f` using a regex. First go:

    In [213]: foo.b.str.match(&#39;f.*&#39;)
    Out[213]: 
    0    []
    1    ()
    2    ()
    3    []

That&#39;s not too terribly useful. However this will get me my boolean index:

    In [226]: foo.b.str.match(&#39;(f.*)&#39;).str.len() &gt; 0
    Out[226]: 
    0    False
    1     True
    2     True
    3    False
    Name: b

So I could then do my restriction by:

    In [229]: foo[foo.b.str.match(&#39;(f.*)&#39;).str.len() &gt; 0]
    Out[229]: 
       a    b
    1  2  foo
    2  3  fat

That makes me artificially put a group into the regex though, and seems like maybe not the clean way to go. Is there a better way to do this?

How to filter rows in pandas by regex

Now, of course, I could write my regular expression to handle both cases, such as `regexp.Compile(&quot;[a-zA-Z]&quot;)`, but my regular expression is constructed from a string given by the user:

    reg, err := regexp.Compile(strings.Replace(s.Name, &quot; &quot;, &quot;[ \\._-]&quot;, -1))

Where `s.Name` is the name.  Which could be something like &#39;North by Northwest&#39;.  Now, the most apparent solution to me would be to walk through each character of `s.Name` and write &#39;[nN]&#39; for each letter:
```go
    for i := 0; i &lt; len(s.Name); i++ {
      if s.Name[i] == &quot; &quot; {
        fmt.Fprintf(str, &quot;%s[ \\._-]&quot;, str);
      } else {
        fmt.Fprintf(str, &quot;%s[%s%s]&quot;, str, strings.ToLower(s.Name[i]), strings.ToUpper(s.Name[i]))
      }
    }
```
But I feel this is a rather non-elegant solution.  Speed is not really a concern, but I need to know if there is another way.

Content Type	Original Author	Original Content on Stackoverflow
Question	Luccas	View Question on Stackoverflow
Solution 1 - Ruby	gpojd	View Answer on Stackoverflow
Solution 2 - Ruby	Mathletics	View Answer on Stackoverflow
Solution 3 - Ruby	gmaliar	View Answer on Stackoverflow

What do `?i` and `?-i` in regex mean?

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Ruby Solutions

Solution 1 - Ruby

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set pythonpath before import statements

Why does TaskCanceledException occur?

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