Python Global Variables

The keyword "global" has a special purpose . If you look into the help docstring of this keyword, you must notice this line :

 It would be impossible to assign to a global variable without "global " 

The word to note is "Assign"

Now . In python , if you declare a variable outside the scope of all functions or classes, it is AVAILABLE GLOBALLY. Meaning I can use it anywhere anytime.

But what is NOT clear , is , you CANNOT change the value\contents of this variable.

Bringing statefulness into your program (e.x an integrating counter ), might need you to keep updating some variable's value . That means, functions must be able to change that value.

Hence, the keyword "global" .

Production server launch using Django and Apache and mod wsgi

Some of us develop Django applications which can be used inside Intranet for various purposes.
Some ideas are:

• HRMS apps
• Interview Management Tools
• Grievance Management Tool
• Financial Report Generators. 

These apps running on intranet, generally don't face too much traffic at a time, but they do need to compute or face heavy queries which is why, it's a good idea to release them on a proper environment . Typically they are light on UI. I choose to use bootstrap which is enough to achieve a decent look . 

Still you should serve them using something which is good at serving static content. So I chose Apache. Lets get started. 

Migrating your Django Project database from SQlite3 to MySQL

Django comes with an in-build default setup for SQLLite3 which is good for learning and minor static page based websites. Like blogs which is a standard example . But as soon you decide to create projects that might entail multiple users performing different operations at the same time, SQLLite is not recommended.

Hence the decision to migrate to a better DB system must be as early as possible. I had to under go a similar experience recently . It look a lot of time, trials to finally get it working . I am going to share you the complete steps assuming you don't even have a MySQL setup .

Quick guide to Logging to a file using Python

This is for setting up of a file logging system using Logging module

Step 1: Import the logging module.

import logging

Step 2: Create a logger for yourself. 

logger = logging.getLogger(__name__)

Working with context processors and WITH statement

We use. We forget. This is for myself so I remember the magic called Context Manager. You already must have used the "with statement" for file handling, threads, socket and other operations. I am going to talk about creating you OWN context managers.

The magic operator to be used is : @contextmanager. It can be imported from the module "contextlib"

To create a context manager, use the decorator contextlib.contextmanager

@contextlib.contextmanager
def getListCounts(x):
    try:
        from collections import Counter
        yield Counter(x)
    finally:
        print 'No of elements in the list : %d' % len(x)

Regular Expressions. Lets not be greedy.

Recently faced a situation when I wanted to extracted parts of a html code. But then I realized, I have no control over the amount of information regex is giving me back.

Python: Running executables using subprocess module

There are many ways to run a bat/exe file but the most widely used is the subprocess module.
And I would like to clearly show, how exactly to do that. When should you use what arguments.
I am going to specifically talk about the check_output module .