Enable CORS in bottle python

To access data of the REST API from other domain API should have CORS enabled for the website. Like most of all framework Bottle by default does not set CORS header. To enable it, following decorator can be used:

In the API response header “Access-Control-Allow-Origin” will be added. As per our example, it will be Access-Control-Allow-Origin: example.com.  To enable it for any website you can set it as “*”.   There is an interesting discussion whether to set it * or not.

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Python super and init explained with example

Python super :

Python super keyword is confusing some time to newbie or even for intermediate python programmers.

But the idea behind super is really simple. In OOP paradigm we often need to do implement inheritance like below:

CODE:

class A(object):

    def fancy_func(self):
        print 'Fancy Function Called from Class A'

class B(A):

    def fancy_func(self):
        return super(B, self).fancy_func()

b is an Object of class B and fancy_func is the method of B, super is returning the base classes method. If we don’t use super,we had declare an object of class A and then we had to call fancy_func. On the other hand,super returns proxy object. Super uses __mro__(method resolution order).

Super can be used:

  • For single inheritance using to refer parent classes
  • In multiple inheritance its very useful in during dynamic execution.

For real life coding when we need to enhance any module method we can easily super to get things done.

And we don’t even have to know details about the base class that we are extending from.

super is only applicable for python new style classes ( the classes derived from object ex. class A(object) )

For python3 the syntax is like below:


super().methoName(args)

Syntax of calling super is like below:

super(subClass, instance).method(args)

Python __init__ :

If you declare a __init__ in your python class, it will be run when you initialize an object from that class.

__init__ acts like constructors in other languages but actually its not. There is a basic major difference between from other methods and __init__,its you cant return anything from it.You can add properties to the current object using like self.myProperty = ‘TEST’ and you can use it in any other method by accessing like self.myProperty

Simply __init__ is used when we want to control the initialization of the class.

Lets build something real with these features:

In the above example we implement both the concept of __init__ and super. Here __init__ using for setting value of url while intilazing the object  and super is being used to call the crawlPyCentral’s getTitles.

To dig more deep into super check this blog post

Factory pattern in Python

We use design pattern to build reusable solution. Building reusable solution is hard and design patterns helps us by giving common design solution for same sort of problems.

One of the important design patterns is Factory Method Pattern. In Python the implementation of factory pattern look like below:

When to use factory pattern?

There are couple of cases when we can use factory pattern, one of the case is- when there is needed to create objects that are dependent on other objects.

That means when we are going to create a complex objects, and complex objects will be based on other objects. When we need to create the complex object we dont need to know the details about other objects that rely on the creation process. Example is like below:

Ideal situation would be, when we see we are coding to gather information to create objects. And factories help to gather object creation in a single place. And also it helps to create decoupled system.

If you have better understanding and experience of using factory pattern in your python code, please share it in comment.

Django merging two QuerySet using itertools.

I was working with a django application where I need to merge two query set. After going through django ORM docs, could not find anything helpful.

I was planning to do it in a unpythonic way like iterating two queryset and appending each item to a new list, just before doing it I thought it would be better to google for it. And after couple of minutes found it. We can use python itertools to merge two or more query set. Like below:

Python itertools is an amazing module that contains real handy methods what we need to handle iterators and doing different types of operation. If you never used  itertools before you are missing one of the charm of python.

Check Itertools chain docs for details.

Happy Coding!

Painless deployment with Fabric

Deployment of code in test/staging/production  servers is one of the important part of modern web applications development cycle.

Deploying code were painful because its repetitive same tasks we have to do every time we want to push code, during deployment  if something goes wrong the application will go down too. But the scenario has changed, now we have many tools to make the deployment easier and fun. I have used Capistrano and Fabric for deployment. Found Fabric really painless and as its a Python battery, it was easier for me to adopt and get things done.

I am going to cover fundamental operations and finally a simple fabric script(like boilerplate) for writing your own fabric script.

env = its a Python dictionary like subclass where we define specific settings like password,user etc

local = runs command in  local host(where fabric script is being run)

run = runs command in a remote host

You can use these code tasks in many different ways, to do that check the Fabric Office Documentation from here.

First gist is a sample fabric script,second one is a bash script to install fabric in your ubuntu machine.

 After setting username,password and host information into the script you cab check your server’s access log by running  fab test_server latest_access_log 

I am using fabric for around two years and used for different small,medium and large projects.

There are many interesting open source projects going on top of Fabric. I found these two projects really promising.

1.Fabtools

2.Graphite_fabric

Search through github,you will find many advance level Fabric use.

Happy Coding!

python csv file reading writting.

Reading and writing to a csv file is fairly simple using python.As python has both reader() and writter() method is  easy to use.In the code below,the script is reading a csv file and appending  row values in different list.the csv file had data in this format

name,link

nam,link

The code below take reads the csv file and take it name to a list and link to another list:

file_path = "path_of_your_csv_file"
shop = csv.reader(open(file_path, "rb"))
shop_list = []
shop_list.extend(shop)
file_name_list = []
rss_link_list = []
for d in shop_list:
file_name_list.append(d[0])
rss_link_list.append(d[1])

And the writing to a csv file was interesting,I tried to write in a csv file and each time when a write was writting data but when a new write operation was executed previous data was erased.Actually,I was missing silly point the I didnt mention the data should be appended when writted.The code was as belows:

def csv_writer(data_list,file_path):
    import csv
    file_p = open(file_path, "wb")
    write_pattern = csv.writer(file_p, delimiter=",", quotechar=",")
    write_pattern.writerow(data_list)
    file_p.close()

In this method user have to pass data and the file path where the csv file will exists should be declared.

You can find more about python csv read write form here