&lt;a href=&quot;http://docs.python.org/reference/datamodel.html#object.__contains__&quot;&gt;`MyClass.__contains__(self, item)`&lt;/a&gt;

A more complete answer is:

    class MyClass(object):
    
        def __init__(self):
            self.numbers = [1,2,3,4,54]
    
        def __contains__(self, key):
            return key in self.numbers

Here you would get `True` when asking if 54 was in `m`:

    &gt;&gt;&gt; m = MyClass()
    &gt;&gt;&gt; 54 in m
    True  

See [documentation on overloading `__contains__`][1].


  [1]: http://docs.python.org/reference/datamodel.html#object.__contains__

You might also want to take a look at an infix operator override framework I was able to use to create a domain-specific language:

http://code.activestate.com/recipes/384122/

Why doesn&#39;t [logcat][1] show anything in my Android (while developing apps with Eclipse)?

It just doesn&#39;t print anything. It&#39;s empty.

  [1]: http://developer.android.com/guide/developing/tools/logcat.html


Why doesn&#39;t logcat show anything in my Android?

I have a PowerShell 1.0 script to just open a bunch of applications. The first is a virtual machine and the others are development applications.  I want the virtual machine to finish booting before the rest of the applications are opened.

In bash I could just say `&quot;cmd1 &amp;&amp; cmd2&quot;`

This is what I&#39;ve got...

    C:\Applications\VirtualBox\vboxmanage startvm superdooper
        &amp;&quot;C:\Applications\NetBeans 6.5\bin\netbeans.exe&quot;



How to tell PowerShell to wait for each command to end before starting the next?

If I am creating my own class in Python, what function should I define so as to allow the use of the `in` operator, e.g.

    class MyClass(object):
        ...
    
    m = MyClass()
    
    if 54 in m:
        ...



Override Python&#39;s &#39;in&#39; operator?

If I am creating my own class in Python, what function should I define so as to allow the use of the <code>in</code> operator, e.g.
<pre><code class="hljs language-vbnet">class MyClass(object):
 ...

m = MyClass()

if 54 in m:
 ...
</code></pre>

How can I find an age in python from today&#39;s date and a persons birthdate? The birthdate is a from a DateField in a  Django model.

Age from birthdate in python

I&#39;ve been looking at dynamic evaluation of Python code, and come across the `eval()` and `compile()` functions, and the `exec` statement.

Can someone please explain the difference between `eval` and `exec`, and how the different modes of `compile()` fit in?

What&#39;s the difference between eval, exec, and compile?

I want to execute a function every 60 seconds on Python but I don&#39;t want to be blocked meanwhile.

How can I do it asynchronously?

    import threading
    import time
    
    def f():
        print(&quot;hello world&quot;)
        threading.Timer(3, f).start()
    
    if __name__ == &#39;__main__&#39;:
        f()    
        time.sleep(20)



With this code, the function f is executed every 3 seconds within the 20 seconds time.time.
At the end it gives an error and I think that it is because the threading.timer has not been canceled.

How can I cancel it?

Thanks in advance!

How to execute a function asynchronously every 60 seconds in Python?

How can I create more than one ModelAdmin for the same model, each customised differently and linked to different URLs?

Let&#39;s say I have a Django model called Posts. By default, the admin view of this model will list all Post objects.

I know I can customise the list of objects displayed on the page in various ways by setting variables like list_display or overriding the `queryset` method in my ModelAdmin like so:


    class MyPostAdmin(admin.ModelAdmin):
        list_display = (&#39;title&#39;, &#39;pub_date&#39;)

        def queryset(self, request):
            request_user = request.user
            return Post.objects.filter(author=request_user)

    admin.site.register(MyPostAdmin, Post)

By default, this would be accessible at the URL `/admin/myapp/post`. However I would like to have multiple views/ModelAdmins of the same model. e.g `/admin/myapp/post` would list all post objects, and `/admin/myapp/myposts` would list all posts belonging to the user, and `/admin/myapp/draftpost` might list all posts that have not yet been published. (these are just examples, my actual use-case is more complex)

You cannot register more than one ModelAdmin for the same model (this results in an `AlreadyRegistered` exception). Ideally I&#39;d like to achieve this **without** putting everything into a single ModelAdmin class and writing my own &#39;urls&#39; function to return a different queryset depending on the URL.

I&#39;ve had a look at the Django source and I see functions like `ModelAdmin.changelist_view` that could be somehow included in my urls.py, but I&#39;m not sure exactly how that would work.

**Update**: I&#39;ve found one way of doing what I want (see below), but I&#39;d still like to hear other ways of doing this.

Multiple ModelAdmins/views for same model in Django admin

I need to subtract *business days* from the current date. 

I currently have some code which needs always to be running on the most recent business day. So that may be today if we&#39;re Monday thru Friday, but if it&#39;s Saturday or Sunday then I need to set it back to the Friday before the weekend. I currently have some pretty **clunky** code to do this:

     lastBusDay = datetime.datetime.today()
     if datetime.date.weekday(lastBusDay) == 5:      #if it&#39;s Saturday
         lastBusDay = lastBusDay - datetime.timedelta(days = 1) #then make it Friday
     elif datetime.date.weekday(lastBusDay) == 6:      #if it&#39;s Sunday
         lastBusDay = lastBusDay - datetime.timedelta(days = 2); #then make it Friday

Is there a better way? 

Can I tell timedelta to work in weekdays rather than calendar days for example? 

Most recent previous business day in Python

I have a question about the return value of operator overloading in C++. Generally, I found two cases, one is return-by-value, and one is return-by-reference. So what&#39;s the underneath rule of that? Especially at the case when you can use the operator continuously, such as `cout&lt;&lt;x&lt;&lt;y`.

For example, when implementing a + operation &quot;string + (string)&quot;. how would you return the return value, by ref or by val.

return value of operator overloading in C++

There are two ways to overload operators for a C++ class:

### Inside class

    class Vector2
    {
    public:
        float x, y ;
        
        Vector2 operator+( const Vector2 &amp; other )
        {
            Vector2 ans ;
            ans.x = x + other.x ;
            ans.y = y + other.y ;
            return ans ;
        }
    } ;


### Outside class
    
    class Vector2
    {
    public:
        float x, y ;
    } ;
    
    Vector2 operator+( const Vector2&amp; v1, const Vector2&amp; v2 )
    {
        Vector2 ans ;
        ans.x = v1.x + v2.x ;
        ans.y = v1.y + v2.y ;
        return ans ;
    }


(Apparently in C# you can only use the &quot;outside class&quot; method.)

In C++, which way is more correct?  Which is preferable?

Operator overloading outside class

In C++, the concept of returning reference from the copy assignment operator is unclear to me. Why can&#39;t the copy assignment operator return a copy of the new object? In addition, if I have class `A`, and the following:

    A a1(param);
    A a2 = a1;
    A a3;
    
    a3 = a2; //&lt;--- this is the problematic line

The `operator=` is defined as follows:

    A A::operator=(const A&amp; a)
    {
    	if (this == &amp;a)
    	{
    		return *this;
    	}
    	param = a.param;
    	return *this;
    }

Why must the copy assignment operator return a reference/const reference?

Is it possible to override operator use in Objective-C?

For example

    myClassInstance + myClassInstance

calls a custom function to add the two.

Can I overload an operator in Objective-C?

How to overload the operator++ in two different ways for postfix `a++` and prefix `++a`?

How to overload the operator++ in two different ways for postfix a++ and prefix ++a?

I am intrigued by the following python expression:

    d3 = dict(d1, **d2)

The task is to merge 2 dictionaries into a third one, and the above expression accomplishes the task just fine. I am interested in the ** operator and what exactly is it doing to the expression. I thought that ** was the power operator and haven&#39;t seen it used in the context above yet.

The full snippet of code is this:

    &gt;&gt;&gt; d1 = {&#39;a&#39;: 1, &#39;b&#39;: 2}
    &gt;&gt;&gt; d2 = {&#39;c&#39;: 3, &#39;d&#39;: 4}
    &gt;&gt;&gt; d3 = dict(d1, **d2)
    &gt;&gt;&gt; print d3
    {&#39;a&#39;: 1, &#39;c&#39;: 3, &#39;b&#39;: 2, &#39;d&#39;: 4}

What does `**` mean in the expression `dict(d1, **d2)`?

What is the correct name for operator `*`, as in `function(*args)`?  unpack, unzip, something else?

proper name for python * operator?

What does Scala&#39;s @ operator do?

For example, in the blog post *[Formal Language Processing in Scala, Part 2][1]* there is a something like this

    case x @ Some(Nil) =&gt; x

  [1]: http://szeiger.de/blog/2008/08/02/formal-language-processing-in-scala-part-2/


Scala @ operator

&gt; **Possible Duplicate:**  
&gt; [The written versions of the logical operators.](https://stackoverflow.com/questions/2376448/the-written-versions-of-the-logical-operators)  

&lt;!-- End of automatically inserted text --&gt;

I notice that C++ define keyword `and`, `or`, `not`, `xor`, `and_eq`, `or_eq`, `not_eq` and `xor_eq` as an alternative to `&amp;&amp;`, `||`, `!`, `^`, `&amp;=`, `|=`, `!=` and `|=`. and they&#39;re rarely used! What&#39;s wrong? Are they not portable?

C++ and,or,not,xor keywords

Apparently a colon is used in multiple ways in Java. Would anyone mind explaining what it does?

For instance here:

	String cardString = &quot;&quot;;
	for (PlayingCard c : this.list)  // &lt;--
	{
		cardString += c + &quot;\n&quot;;
	}

How would you write this `for-each` loop a different way so as to not incorporate the `:`?

What does the colon (:) operator do?

Why does the &quot;in&quot; operator in Javascript return true when testing if &quot;0&quot; exists in array, even when the array doesn&#39;t appear to contain &quot;0&quot;?

For example, this returns true, and makes sense:

    var x = [1,2];
    1 in x; // true

This returns false, and makes sense:

    var x = [1,2];
    3 in x; // false

However this returns true, and I don&#39;t understand why:

    var x = [1,2];
    0 in x;


Why does javascript&#39;s &quot;in&quot; operator return true when testing if 0 exists in an array that doesn&#39;t contain 0?

In SQL, you can use the following syntax:

    SELECT *
    FROM MY_TABLE
    WHERE VALUE_1 IN (1, 2, 3)

Is there an equivalent in C#?  The IDE seems to recognise &quot;in&quot; as a keyword, but I don&#39;t seem to be able to find any information on it.

So, is it possible to do something like the following:

    int myValue = 1;
    if (myValue in (1, 2, 3))
        // Do something
    
Instead of


    int myValue = 1;
    if (myValue == 1 || myValue == 2 || myValue == 3)
        // Do something


Is there a C# IN operator?

How does SQL engines differ when we use equal sign and IN operator have same value? Does execution time changes?

1st one using equality check operator

    WHERE column_value = &#39;All&#39;

2nd one using `IN` operator and single value

    WHERE column_value IN (&#39;All&#39;)

Does SQL engine changes `IN` to `=` if only one value is there?

Is there any difference for same in MySQL and PostgreSQL?

Content Type	Original Author	Original Content on Stackoverflow
Question	astrofrog	View Question on Stackoverflow
Solution 1 - Python	Ignacio Vazquez-Abrams	View Answer on Stackoverflow
Solution 2 - Python	pthulin	View Answer on Stackoverflow
Solution 3 - Python	user250828	View Answer on Stackoverflow

Override Python's 'in' operator?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Solution 3 - Python

How to tell PowerShell to wait for each command to end before starting the next?

Why doesn't logcat show anything in my Android?

Attributions