Python? , But why Python?

Well I am using python since last 3 years . It has been my main development language, other than javascript.

Often, someone comes around and asks , Why Python? I am usually left with my personal programming tasks where python comes in very handy when compared to other languages I have encountered, like  PHP or Java.

Well , here is a post for answering this question exactly. Check it here.

Here are the points -

• Efficient - Has generators 
• Fast
• Broad use
• Not just a language, has a number of implementations
• Easy

Cheers!!

Yet another post on Redis

While working for a project , we used Redis as queue, using python-rq.  Running a redis-cli , I used the following commands -

• keys *
• type <key name>
• and then according to the type , hash,list I would query the data

Some things were quite easy to understand

• rq:workers
• rq:queue:failed
• rq:queue:default
• and a success one as well

But apart from these, there were several entries - with name rq:job:<job_id>. After much reading, I found the internal working at http://python-rq.org/contrib/.

It says whenever a function call gets enqueued - 

• Pushes the job's ids into queue , in my case the default
• adds a hash objects of the job instance

So, when dequeue happens - 

• Pops jobid from queue
• Fetches Job data 
• Executes the function and saves result has a hash key if success
• else saves in failed queue with stack trace

All of this is given on Python-rq site.

There are two kinds of error I saw -

• RuntimeError: maximum recursion depth exceeded while calling a Python object - This happened at queue.py of python-rq module, where I think, it was caused when control crossed max recursive limit, when it didnt find the jobs hashes, as discussed above in dequeue
• Socket closed on remote end - The server closes client connection after 300s, in my case I didnt want to do them, so. let it be on forever by changing in /etc/redis/redis.conf , timeout value to 0

Go Redis!!

Python Decorators - The correct way to do it

Was going through Graham Dumpleton's blog post - how you implemented your python decorator is wrong. Simple points that were discussed were -

• Decorators can be functions as well as Classes.
  

  As a class -  

  
  

  class function_wrapper(object):
      def __init__(self, wrapped):
          self.wrapped = wrapped
      def __call__(self, *args, **kwargs):
          return self.wrapped(*args, **kwargs) 

  @function_wrapper
  def function():
      pass 

  
  

  As a function 

  
  

  def function_wrapper(wrapped):
      def _wrapper(*args, **kwargs):
          return wrapped(*args, **kwargs)
      return _wrapper 

  @function_wrapper
  def function():
      pass 

  
  

• Use the functools.wraps decorator , it only preserves original functions __name__ and __class__
  

  In functions 

  
  

  import functools 

  def function_wrapper(wrapped):
      @functools.wraps(wrapped)
      def _wrapper(*args, **kwargs):
          return wrapped(*args, **kwargs)
      return _wrapper 

  @function_wrapper
  def function():
      pass 

  
  

  In classes, use the update_wrapper method- 

  
  

  import functools 

  class function_wrapper(object):
      def __init__(self, wrapped):
          self.wrapped = wrapped
          functools.update_wrapper(self, wrapped)
      def __call__(self, *args, **kwargs):
          return self.wrapped(*args, **kwargs)

• Python 2.7 preserves Argument specification ( inspect.getargspec ) only in functional decorators, not in class based ones.
• Doesnt preserve function source code for inspection ( inspect.getsource ) 
• Cannot apply decorators on top of other decorators that are implemented as descriptors.

Failed to attach to key daemon - Error in Shrew Soft VPN

Using Shrew Soft VPN on Ubuntu 12.04, I often face this error

Failed to attach to key daemon 

On some googling I found this post -> Ubuntu Forums

It says that this error is because IKE Daemon isnt running.

sudo iked

Hope this helps.