In Python, one file is called a [**module**][1]. A module can consist of **multiple** classes or functions.

As Python is **not** an OO language only, it does not make sense do have a rule that says, one file should only contain one class.

One file (module) should contain classes / functions that belong together, i.e. provide similar functionality or depend on each other.  
Of course you should not exaggerate this. Readability really suffers if your module consist of too much classes or functions. Then it is probably time to regroup the functionality into different modules and create [packages][2].

----------

For naming conventions, you might want to read [PEP 8][3] but in short:

&gt; **Class Names**

&gt;    Almost without exception, class names use the CapWords convention.
      Classes for internal use have a leading underscore in addition.

and

&gt;**Package and Module Names**

&gt;  Modules should have short, all-lowercase names.  Underscores can be used
      in the module name if it improves readability.  Python packages should
      also have short, all-lowercase names, although the use of underscores is
      discouraged.

&gt;   Since module names are mapped to file names, and some file systems are
      case insensitive and truncate long names, it is important that module
      names be chosen to be fairly short -- this won&#39;t be a problem on Unix,
      but it may be a problem when the code is transported to older Mac or
      Windows versions, or DOS.

----------

To instantiate an object, you have to import the class in your file. E.g

    &gt;&gt;&gt; from mymodule import MyClass
    &gt;&gt;&gt; obj = MyClass()

or

    &gt;&gt;&gt; import mymodule
    &gt;&gt;&gt; obj = mymodule.MyClass()

or

    &gt;&gt;&gt; from mypackage.mymodule import MyClass
    &gt;&gt;&gt; obj = MyClass()


----------

**You are asking essential basic stuff, so I recommend to read the [tutorial][4].**


  [1]: http://docs.python.org/tutorial/modules.html
  [2]: http://docs.python.org/tutorial/modules.html#packages
  [3]: http://www.python.org/dev/peps/pep-0008/
  [4]: http://docs.python.org/tutorial/

No, you can define multiple classes (and functions, etc.) in a single file. A file is also called a module.

To use the classes/functions defined in the module/file, you will need to `import` the module/file.

I have a Postgre database that has say 10 columns. The fifth column is called `column5`. There are 100 rows in the database and possible values of `column5` are `c5value1, c5value2, c5value3...c5value29, c5value30`. I would like to print out a table that shows how many times each value occurs. 

So the table would look like this:

    Value(of column5)          number of occurrences of the value
         c5value1                              1
         c5value2                              5
         c5value3                              3
         c5value4                              9
         c5value5                              1
         c5value6                              1
            .                                  .
            .                                  .
            .                                  .

What is the command that does that?


How to count number of occurrences for all different values in database column?

&gt; **Possible Duplicate:**  
&gt; [Detecting if a browser is in full screen mode](https://stackoverflow.com/questions/1047319/detecting-if-a-browser-is-in-full-screen-mode)  

&lt;!-- End of automatically inserted text --&gt;

Is there a way to check if a browser is currently in fullscreen mode (after the user pressed f11)?

Something like:

    if (window.fullscreen) {
      // it&#39;s fullscreen!
    }
    else {
      // not fs!
    }

Thanks.

Steerpike&#39;s answer is pretty good, but my comment:

&gt; Thanks a lot, but this answer is not
&gt; sufficient for FF. In Chrome I can set
&gt; a small tolerance, but in FF the
&gt; urlbar and tabs takes a while to
&gt; disappear, which means after pressing
&gt; f11, the detected window.innerWidth is
&gt; still too small.

Checking if browser is in fullscreen

Much like Java (or php), I&#39;m use to seperating the classes to files. &lt;br&gt;
Is it the same deal in Python? plus, how should I name the file? &lt;br&gt;
Lowercase like classname.py or the same like ClassName.py? &lt;br&gt;
Do I need to do something special if I want to create an object from this class or does the fact that it&#39;s in the same &quot;project&quot; (netbeans) makes it ok to create an object from it?

Are classes in Python in different files?

Much like Java (or php), I'm use to seperating the classes to files. 
Is it the same deal in Python? plus, how should I name the file? 
Lowercase like classname.py or the same like ClassName.py? 
Do I need to do something special if I want to create an object from this class or does the fact that it's in the same "project" (netbeans) makes it ok to create an object from it?

    def common_elements(list1, list2):
        &quot;&quot;&quot;
        Return a list containing the elements which are in both list1 and list2
    
        &gt;&gt;&gt; common_elements([1,2,3,4,5,6], [3,5,7,9])
        [3, 5]
        &gt;&gt;&gt; common_elements([&#39;this&#39;,&#39;this&#39;,&#39;n&#39;,&#39;that&#39;],[&#39;this&#39;,&#39;not&#39;,&#39;that&#39;,&#39;that&#39;])
        [&#39;this&#39;, &#39;that&#39;]
        &quot;&quot;&quot;
        for element in list1:
            if element in list2:
                return list(element)

Got that so far, but can&#39;t seem to get it to work! 

Any ideas?

Common elements comparison between 2 lists

I&#39;ve a python script which works just as it should, but I need to write the execution time. I&#39;ve googled that I should use [`timeit`](https://docs.python.org/2/library/timeit.html) but I can&#39;t seem to get it to work.

My Python script looks like this:

    import sys
    import getopt
    import timeit
    import random
    import os
    import re
    import ibm_db
    import time
    from string import maketrans
    myfile = open(&quot;results_update.txt&quot;, &quot;a&quot;)
   
    for r in range(100):
    	rannumber = random.randint(0, 100)
    
    	update = &quot;update TABLE set val = %i where MyCount &gt;= &#39;2010&#39; and MyCount &lt; &#39;2012&#39; and number = &#39;250&#39;&quot; % rannumber
    	#print rannumber
    	
    	conn = ibm_db.pconnect(&quot;dsn=myDB&quot;,&quot;usrname&quot;,&quot;secretPWD&quot;)
     
    for r in range(5):
    	print &quot;Run %s\n&quot; % r        
        ibm_db.execute(query_stmt)
   	 query_stmt = ibm_db.prepare(conn, update)
    	
    myfile.close()
    ibm_db.close(conn)

What I need is the time it takes to execute the query and write it to the file `results_update.txt`. The purpose is to test an update statement for my database with different indexes and tuning mechanisms.

How can I time a code segment for testing performance with Pythons timeit?

I just finished my second year as a university CS student, so my &quot;real-world&quot; knowledge is lacking.  I learned Java my first year, continued with Java and picked up C and simple Bash 
scripting my second.  This summer I&#39;m trying to learn Perl (God help me).  I&#39;ve dabbled with Python a bit in the past.

My question is, now that we have very readable, very writable scripting languages like Python, Ruby, Perl, etc, why does anyone write Bash scripts?  Is there something I&#39;m missing?  I know my linux box has perl and python.  Are they not ubiquitous enough?  Is there really something
that&#39;s easier to do in Bash than in some other hll?

Is there any use for Bash scripting anymore?

How does one truncate a string to 75 characters in Python?

This is how it is done in JavaScript:
 
    var data=&quot;saddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddsaddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddsadddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddddd&quot;
    var info = (data.length &gt; 75) ? data.substring[0,75] + &#39;..&#39; : data;


Python truncate a long string

How do I check if daylight saving time is in effect?

Python daylight savings time

I would like to differentiate between following cases:

 1. A plain value type (e.g. `int`)
 2. A nullable value type (e.g. `int?`)
 3. A reference type (e.g. `string`) - optionally, I would not care if this mapped to (1) or (2) above

I have come up with the following code, which works fine for cases (1) and (2):

    static void Foo&lt;T&gt;(T a) where T : struct { } // 1

    static void Foo&lt;T&gt;(T? a) where T : struct { } // 2

However, if I try to detect case (3) like this, it does not compile:

    static void Foo&lt;T&gt;(T a) where T : class { } // 3

The error message is _Type &#39;X&#39; already defines a member called &#39;Foo&#39; with the same parameter types_. Well, somehow I cannot make a difference between `where T : struct` and `where T : class`.

If I remove the third function (3), the following code does not compile either:

    int x = 1;
    int? y = 2;
    string z = &quot;a&quot;;

    Foo (x); // OK, calls (1)
    Foo (y); // OK, calls (2)
    Foo (z); // error: the type &#39;string&#39; must be a non-nullable value type ...

How can I get `Foo(z)` to compile, mapping it to one of the above functions (or a third one with another constraint, which I have not thought of)?

Generic constraints, where T : struct and where T : class

`myclass` is a C++ class written by me and when I write:

    myclass x;
    cout &lt;&lt; x;

How do I output `10` or `20.2`, like an `integer` or a `float` value?

How can I use cout &lt;&lt; myclass

What is the difference between `sealed abstract` and `abstract` Scala class?

Scala&#39;s sealed abstract vs abstract class

I am working with classes and object class structure, but not at a complex level – just classes and functions, then, in one place, instantiation.

As to `__construct` and `__destruct`, please tell me very simply: **what is the purpose of constructors and destructors**?

I know the school level theoretical explanation, but i am expecting something like in real world, as in which situations we have to use them.

Provide also an example, please.

Regards


Purpose of PHP constructors

I&#39;m writing a lightweight class whose attributes are intended to be publicly accessible, and only sometimes overridden in specific instantiations.  There&#39;s no provision in the Python language for creating docstrings for class attributes, or any sort of attributes, for that matter.  What is the expected and supported way, should there be one, to document these attributes?  Currently I&#39;m doing this sort of thing:

    class Albatross(object):
        &quot;&quot;&quot;A bird with a flight speed exceeding that of an unladen swallow.

        Attributes:
        &quot;&quot;&quot;
    
        flight_speed = 691
        __doc__ += &quot;&quot;&quot;
            flight_speed (691)
              The maximum speed that such a bird can attain.
        &quot;&quot;&quot;
    
        nesting_grounds = &quot;Raymond Luxury-Yacht&quot;
        __doc__ += &quot;&quot;&quot;
            nesting_grounds (&quot;Raymond Luxury-Yacht&quot;)
              The locale where these birds congregate to reproduce.
        &quot;&quot;&quot;
    
        def __init__(self, **keyargs):
            &quot;&quot;&quot;Initialize the Albatross from the keyword arguments.&quot;&quot;&quot;
            self.__dict__.update(keyargs)

This will result in the class&#39;s docstring containing the initial standard docstring section, as well as the lines added for each attribute via augmented assignment to `__doc__`.

Although this style doesn&#39;t seem to be expressly forbidden in the [docstring style guidelines][1], it&#39;s also not mentioned as an option.  The advantage here is that it provides a way to document attributes alongside their definitions, while still creating a presentable class docstring, and avoiding having to write comments that reiterate the information from the docstring.  I&#39;m still kind of annoyed that I have to actually write the attributes twice; I&#39;m considering using the string representations of the values in the docstring to at least avoid duplication of the default values.

Is this a heinous breach of the ad hoc community conventions?  Is it okay?  Is there a better way?  For example, it&#39;s possible to create a dictionary containing values and docstrings for the attributes and then add the contents to the class `__dict__` and docstring towards the end of the class declaration; this would alleviate the need to type the attribute names and values twice.  **edit**: this last idea is, I think, not actually possible, at least not without dynamically building the entire class from data, which seems like a really bad idea unless there&#39;s some other reason to do that.

I&#39;m pretty new to python and still working out the details of coding style, so unrelated critiques are also welcome.


  [1]: http://www.python.org/dev/peps/pep-0257/

How to document class attributes in Python?

Where can I find a detailed manual about PostgreSQL naming conventions? (table names vs. camel case, sequences, primary keys, constraints, indexes, etc...)


PostgreSQL naming conventions

In some interfaces I wrote I&#39;d like to name generic type parameters with more than one character to make the code more readable.

Something like....

    Map&lt;Key,Value&gt;

Instead of this...

    Map&lt;K,V&gt;

But when it comes to methods, the type-parameters look like java-classes which is also confusing.

    public void put(Key key, Value value)

This seems like Key and Value are classes. I found or thought of some notations, but nothing like a convention from Sun or a general best-practice.

Alternatives I guessed or found...

    Map&lt;KEY,VALUE&gt;
    Map&lt;TKey,TValue&gt;
    



Generic type parameter naming convention for Java (with multiple chars)?

In the C language where did they come up with the name `atoi` for converting a string to an integer? The only thing I can think of is Array To Integer for an acronym but that doesn&#39;t really make sense. 

Where did the name `atoi` come from?


I have &#39;Service&#39; table and the following column description as below &lt;Br/&gt;

 1. Is User Verification Required for service ?
 2. Is User&#39;s Email Activation Required for the service ?
 3. Is User&#39;s Mobile Activation required for the service ?

I Hesitate in naming these columns as below &lt;br/&gt;

    IsVerificationRequired
    IsEmailActivationRequired
    IsMobileActivationRequired

or

    RequireVerification
    RequireEmailActivation
    RequireMobileActivation


**I can&#39;t determined which way is the best  .So, Is one of the above suggested name is the best or is there other better ones ?**


Naming of boolean column in database table

Is there a convention for naming enumerations in Java?

My preference is that an enum is a type.  So, for instance, you have an enum 

    Fruit{Apple,Orange,Banana,Pear, ... }

    NetworkConnectionType{LAN,Data_3g,Data_4g, ... }

I am opposed to naming it:

    FruitEnum
    NetworkConnectionTypeEnum

I understand it is easy to pick off which files are enums, but then you would also have:

    NetworkConnectionClass
    FruitClass

Also, is there a good document describing the same for constants, where to declare them, etc.?


Content Type	Original Author	Original Content on Stackoverflow
Question	Asaf	View Question on Stackoverflow
Solution 1 - Python	Felix Kling	View Answer on Stackoverflow
Solution 2 - Python	Chris Henry	View Answer on Stackoverflow

Are classes in Python in different files?

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Checking if browser is in fullscreen

How to count number of occurrences for all different values in database column?

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