There are several REPLs for Ruby.

The standard library ships with a REPL called *IRb* (for *Interactive Ruby*), which installs a program named `irb`, but since it is just a Ruby library, it can also be invoked from Ruby code and not just from the shell. On [Rubinius](http://Rubini.us/), IRb can also be invoked by just calling the `rbx` program without arguments, just like in CPython.

There is also a very nice REPL called [*Pry*](http://PryREPL.Org/), which installs a program named `pry`, but since it is just a Ruby library, it can also be invoked from Ruby code and not just from the shell.

[JRuby](http://JRuby.Org/) comes with an additional REPL called *JIRb Swing*, which is invoked by calling the `jirb_swing` program.

The [NetBeans](http://NetBeans.Org/) Ruby Plugin also comes with a REPL.

Use the `irb` (Interactive Ruby Shell) command.

https://en.wikipedia.org/wiki/Interactive_Ruby_Shell

I am trying to automate download of historic stock data using python. The URL I am trying to open responds with a CSV file, but I am unable to open using urllib2. I have tried changing user agent as specified in few questions earlier, I even tried to accept response cookies, with no luck. Can you please help. 

*Note: The same method works for yahoo Finance.*

**Code:**

    import urllib2,cookielib
    
    site= &quot;http://www.nseindia.com/live_market/dynaContent/live_watch/get_quote/getHistoricalData.jsp?symbol=JPASSOCIAT&amp;fromDate=1-JAN-2012&amp;toDate=1-AUG-2012&amp;datePeriod=unselected&amp;hiddDwnld=true&quot;
    
    hdr = {&#39;User-Agent&#39;:&#39;Mozilla/5.0&#39;}
    
    req = urllib2.Request(site,headers=hdr)
    
    page = urllib2.urlopen(req)

**Error**
  

&gt; File &quot;C:\Python27\lib\urllib2.py&quot;, line 527, in http_error_default
&gt;     raise HTTPError(req.get_full_url(), code, msg, hdrs, fp) urllib2.HTTPError: HTTP Error 403: Forbidden


Thanks for your assistance

urllib2.HTTPError: HTTP Error 403: Forbidden

I am trying to perform some DDL on a table and `SHOW PROCESSLIST` results in a &quot; Waiting for table metadata lock &quot; message.

How can I find out which transaction is not yet closed?

I&#39;m using MySQL v5.5.24.

How do I find which transaction is causing a &quot;Waiting for table metadata lock&quot; state?

What command opens Ruby&#39;s REPL?

In Python, you simply open `python` without any arguments.

What command opens Ruby&#39;s REPL?

<p>What command opens Ruby's REPL?</p>
<p>In Python, you simply open <code>python</code> without any arguments.</p>


In Ruby, is there a way to &#39;override&#39; a constant in a subclass in such a way that calling an inherited method from the subclass results in that method using the new constant instead of the old one? For example:

    class SuperClass
      CONST = &quot;Hello, world!&quot;
      def self.say_hello
        CONST
      end
    end
    
    class SubClass &lt; SuperClass
      override_const :CONST, &quot;Hello, Bob!&quot;
    end
    
    SuperClass.say_hello # =&gt; &quot;Hello, world!&quot;
    SubClass.say_hello   # =&gt; &quot;Hello, Bob!&quot;

If not, is there perhaps a way to do something like this instead?

    class SuperClass
      CONST = &quot;Hello, world!&quot;
      def self.say_hello
        CONST
      end
    end

    SubClass = SuperClass.clone
    SubClass.send(:remove_const, :CONST)
    SubClass.const_set(:CONST, &quot;Hello, Bob!&quot;)
    
    SubClass.say_hello # =&gt; &quot;Hello, Bob!&quot;

----------

Note: I tried my second example out in irb, and it seems to work except that class methods can&#39;t seem to access CONST after I clone the class:

    irb(main):012:0&gt; SubClass.say_hello
    NameError: uninitialized constant Class::CONST
            from (irb):4:in `say_hello&#39;
            from (irb):12
            from C:/Ruby193/bin/irb:12:in `&lt;main&gt;&#39;

Override ruby constant in subclass so inherited methods use new constant instead of the old?

If I, say, loop through all the instances of a given model and output something from each, at the end, irb will still print the entire object. 

If the object ends up taking hundreds of lines, it&#39;ll be a long way up before I see what I was actually looking for. Is there a way to disable this in the rails console?

Stop rails console from printing out the object at the end of a loop

Is there a shorter way to find the first element in an array meeting some conditions than this:

    my_array[ my_array.index {|x| x.some_test} ]


First element of an array with condition

In python there is a `pass` keyword for defining an empty function, condition, loop, ...
Is there something similar for Ruby?

Python Example:

    def some_function():
        # do nothing
        pass

Equivalent of “pass” in Ruby

I have a `map` which either changes a value or sets it to nil. I then want to remove the nil entries from the list. The list doesn&#39;t need to be kept.

This is what I currently have:

&lt;!-- language: lang-rb --&gt;

    # A simple example function, which returns a value or nil
    def transform(n)
      rand &gt; 0.5 ? n * 10 : nil }
    end
    
    items.map! { |x| transform(x) } # [1, 2, 3, 4, 5] =&gt; [10, nil, 30, 40, nil]
    items.reject! { |x| x.nil? } # [10, nil, 30, 40, nil] =&gt; [10, 30, 40]

I&#39;m aware I could just do a loop and conditionally collect in another array like this:

&lt;!-- language: lang-rb --&gt;

    new_items = []
    items.each do |x|
        x = transform(x)
        new_items.append(x) unless x.nil?
    end
    items = new_items

But it doesn&#39;t seem that idiomatic. Is there a nice way to map a function over a list, removing/excluding the nils as you go?

How to map and remove nil values in Ruby

I saw a reference to creating a &quot;REPL&quot;.  What is a REPL?

    var arDrone = require(&#39;ar-drone&#39;);
    var client  = arDrone.createClient();
    client.createRepl();


What is a &quot;REPL&quot; in javascript?

When debugging Python code at the interactive prompt (REPL), often I&#39;ll write some code which raises an exception, but I haven&#39;t wrapped it in a `try`/`except`, so once the error is raised, I&#39;ve forever lost the exception object.

Often the traceback and error message Python prints out isn&#39;t enough. For example, when fetching a URL, the server might return a 40x error, and you need the content of the response via `error.read()` ... but you haven&#39;t got the error object anymore. For example:

    &gt;&gt;&gt; import urllib2
    &gt;&gt;&gt; f = urllib2.urlopen(&#39;http://example.com/api/?foo=bad-query-string&#39;)
    Traceback (most recent call last):
      File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
      ...
    urllib2.HTTPError: HTTP Error 400: Bad Request

Drat, what did the body of the response say? It probably had valuable error information in it...

I realize it&#39;s usually easy to re-run your code wrapped in a try/except, but that&#39;s not ideal. I also realize that in this specific case if I were using the `requests` library (which doesn&#39;t raise for HTTP errors), I wouldn&#39;t have this problem ... but I&#39;m really wondering if there&#39;s a more general way to get the last exception object at a Python prompt in these cases.


How to get the last exception object after an error is raised at a Python prompt?

I created this function in Python 2.7 with `ipython`:

    def _(v):
        return v

later if I call `_(somevalue)`, I get `_ = somevalue`.

    in[3]: _(3)
    out[3]: 3
    in[4]: print _
    out[4]: 3

The function has disappeared! If I call `_(4)` I get:

```none
TypeError: &#39;int&#39; object is not callable
```

Why? What&#39;s wrong with this function?


Assigning a value to single underscore _ in Python/IPython interpreter

I&#39;ve downloaded **Algebird** and I want to try out few things in the **Scala interpreter** using this library. How do I achieve this? 

How to use third party libraries with Scala REPL?

I read [What&#39;s new in Xcode 6][1]. The article introduces some new feature about Xcode 6, and it says:
&gt;Command Line
&gt;
&gt;Xcode’s debugger includes an interactive version of the Swift language, known as the REPL (Read-Eval-Print-Loop). Use Swift syntax to evaluate and interact with your running app or write new code in a script-like environment. The REPL is available from within LLDB in Xcode’s console, or from Terminal.

I want to know how to get the REPL?


  [1]: https://developer.apple.com/xcode/

Content Type	Original Author	Original Content on Stackoverflow
Question	Jian	View Question on Stackoverflow
Solution 1 - Ruby	Jörg W Mittag	View Answer on Stackoverflow
Solution 2 - Ruby	Jian	View Answer on Stackoverflow

What command opens Ruby's REPL?

Ruby Problem Overview

Ruby Solutions

Solution 1 - Ruby

Solution 2 - Ruby

How do I find which transaction is causing a "Waiting for table metadata lock" state?

urllib2.HTTPError: HTTP Error 403: Forbidden

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