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.

Solving failed to load canberra-gtk-module error on precise.

I have Ubuntu Precise(12.04) 64 bit.

On openinig sublime, it gave me this error -

(sublime:7247): Gtk-WARNING **: Unable to locate theme engine in module_path: "murrine",

(sublime:7247): Gtk-WARNING **: Unable to locate theme engine in module_path: "murrine",

(sublime:7247): Gtk-WARNING **: Unable to locate theme engine in module_path: "murrine",

Gtk-Message: Failed to load module "canberra-gtk-module"

'import site' failed; use -v for traceback

`menu_proxy_module_load': sublime: undefined symbol: menu_proxy_module_load

(sublime:7247): Gtk-WARNING **: Failed to load type module: (null)

on running strace on sublime ,

I got this output  -

access("/usr/lib/i386-linux-gnu/gtk-2.0/modules/libcanberra-gtk-module.la", F_OK) = -1 ENOENT (No such file or directory)

access("/usr/lib/gtk-2.0/2.10.0/i686-pc-linux-gnu/modules/libcanberra-gtk-module.so", F_OK) = -1 ENOENT (No such file or directory)

access("/usr/lib/gtk-2.0/2.10.0/i686-pc-linux-gnu/modules/libcanberra-gtk-module.la", F_OK) = -1 ENOENT (No such file or directory)

access("/usr/lib/gtk-2.0/2.10.0/modules/libcanberra-gtk-module.so", F_OK) = -1 ENOENT (No such file or directory)

access("/usr/lib/gtk-2.0/2.10.0/modules/libcanberra-gtk-module.la", F_OK) = -1 ENOENT (No such file or directory)

access("/usr/lib/gtk-2.0/i686-pc-linux-gnu/modules/libcanberra-gtk-module.so", F_OK) = -1 ENOENT (No such file or directory)

access("/usr/lib/gtk-2.0/i686-pc-linux-gnu/modules/libcanberra-gtk-module.la", F_OK) = -1 ENOENT (No such file or directory)

access("/usr/lib/gtk-2.0/modules/libcanberra-gtk-module.so", F_OK) = -1 ENOENT (No such file or directory)

access("/usr/lib/gtk-2.0/modules/libcanberra-gtk-module.la", F_OK) = -1 ENOENT (No such file or directory)

stat64("libcanberra-gtk-module.so", {st_mode=S_IFREG|0644, st_size=23072, ...}) = 0

open("/lib/i386-linux-gnu/libcanberra-gtk-module.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)

open("/usr/lib/i386-linux-gnu/sse2/libcanberra-gtk-module.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)

open("/usr/lib/i386-linux-gnu/libcanberra-gtk-module.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)

open("/lib/libcanberra-gtk-module.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)

open("/usr/lib/libcanberra-gtk-module.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)

write(2, "Gtk-Message: Failed to load modu"..., 57Gtk-Message: Failed to load module "canberra-gtk-module"

 As the error says, it was trying to locate libcanberra-gtk-module.so in a number of locations.

Googling the package name , I saw that the location in which it was trying to find was wrong, in locations where 32bit packages are there.

There was the solution. I was trying to load 32 bit Sublime Text on 64 bit system. Downloading a 64 bit version worked like a charm.

Ejabberd Dissection

Working on Ejabbered 2.1.13, in order to understand ejabbered db calls and processes, I followed this presentation  - http://www.slideshare.net/ShaojieYang/ejabberd-installation-configuration-15508995
.
 It showed an easy process to connect Ejabberd to an external database.
Here I would be going a step ahead and saving the DB calls Ejabberd makes, assuming this will be same, when it using its internal Mnesia DB.

When adding a new user(registration)  from web admin - test3@192.168.1.250
----------------------------------------------------------------------------------------------------------
  113 Query select password from users where username='admin'
  112 Query select password from users where username='admin'
  112 Query select password from users where username='test3'

  104 Query insert into users(username, password) values ('test3', 'test3')

Below for count for Offline Messages and  Last Activity shown in admin
-----------------------------------------------------------------------
108 Query select username from users
104 Query select count(*) from spool  where username='admin'
104 Query select seconds, state from last where username='admin'
107 Query select count(*) from spool  where username='admin3'
108 Query select seconds, state from last where username='admin3'

Connecting a user - test2@192.168.1.250
-------------------------------------------------------
109 Query select password from users where username='test2'
113 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test2'
104 Query select name from privacy_default_list where username='test2'
105 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test2'
112 Query select jid, grp from rostergroups where username='test2'
109 Query select password from users where username='test2'
113 Query select name from privacy_default_list where username='test2'
105 Query select name from privacy_list where username='test2'
105 Query select id from privacy_list where username='test2' and name='invisible'
110 Query begin
110 Query select id from privacy_list where username='test2' and name='invisible'
110 Query insert into privacy_list(username, name) values ('test2', 'invisible')
110 Query select id from privacy_list where username='test2' and name='invisible'
110 Query delete from privacy_list_data where id='1'
110 Query insert into privacy_list_data(id, t, value, action, ord, match_all, match_iq, match_message, match_presence_in, match_presence_out ) values ('1', 'n', '', 'd', '1', '0', '0', '0', '0', '1')
110 Query commit
104 Query begin
104 Query select username, xml from spool where username='test2'  order by seq
104 Query delete from spool where username='test2'
104 Query commit
108 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test2'
110 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test2'
113 Query select jid, grp from rostergroups where username='test2'
105 Query select subscription from rosterusers where username='test2' and jid='test2@192.168.1.250'
112 Query select subscription from rosterusers where username='test2' and jid='test2@192.168.1.250'
112 Query select subscription from rosterusers where username='test2' and jid='test2@192.168.1.250'
104 Query select subscription from rosterusers where username='test2' and jid='test2@192.168.1.250'

111 Query select subscription from rosterusers where username='test2' and jid='test2@192.168.1.250'

Adding contact - test1@192.168.1.250 by test4
--------------------------------------------------------------

122 Query begin
122 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test4' and jid='test1@192.168.1.250'
122 Query update rosterusers set username='test4', jid='test1@192.168.1.250', nick='', subscription='N', ask='N', askmessage='', server='N', subscribe='', type='item' where username='test4' and jid='test1@192.168.1.250'
122 Query insert into rosterusers(username, jid, nick, subscription, ask, askmessage, server, subscribe, type) values ('test4', 'test1@192.168.1.250', '', 'N', 'N', '', 'N', '', 'item')
122 Query delete from rostergroups       where username='test4'         and jid='test1@192.168.1.250'
122 Query commit
131 Query begin
131 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test4' and jid='test1@192.168.1.250'
131 Query select grp from rostergroups where username='test4' and jid='test1@192.168.1.250'
131 Query update rosterusers set username='test4', jid='test1@192.168.1.250', nick='', subscription='N', ask='O', askmessage='', server='N', subscribe='', type='item' where username='test4' and jid='test1@192.168.1.250'
131 Query commit
129 Query select name from privacy_default_list where username='test1'
128 Query select password from users where username='test1'
123 Query begin
123 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test1' and jid='test4@192.168.1.250'
123 Query update rosterusers set username='test1', jid='test4@192.168.1.250', nick='', subscription='N', ask='I', askmessage='', server='N', subscribe='', type='item' where username='test1' and jid='test4@192.168.1.250'
123 Query insert into rosterusers(username, jid, nick, subscription, ask, askmessage, server, subscribe, type) values ('test1', 'test4@192.168.1.250', '', 'N', 'I', '', 'N', '', 'item')
123 Query commit

Now asks for permission 

in rosterusers table - subscription field is N (related to pending as others which are already accepted contacts have B) and  ask field is O for test4 and I for test1 (test4 added test1)

Ater accepting

-------------------

122 Query begin

122 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test4' and jid='test1@192.168.1.250'

122 Query update rosterusers set username='test4', jid='test1@192.168.1.250', nick='', subscription='N', ask='N', askmessage='', server='N', subscribe='', type='item' where username='test4' and jid='test1@192.168.1.250'

122 Query insert into rosterusers(username, jid, nick, subscription, ask, askmessage, server, subscribe, type) values ('test4', 'test1@192.168.1.250', '', 'N', 'N', '', 'N', '', 'item')

122 Query delete from rostergroups       where username='test4'         and jid='test1@192.168.1.250'

122 Query commit

131 Query begin

131 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test4' and jid='test1@192.168.1.250'

131 Query select grp from rostergroups where username='test4' and jid='test1@192.168.1.250'

131 Query update rosterusers set username='test4', jid='test1@192.168.1.250', nick='', subscription='N', ask='O', askmessage='', server='N', subscribe='', type='item' where username='test4' and jid='test1@192.168.1.250'

131 Query commit

129 Query select name from privacy_default_list where username='test1'

128 Query select password from users where username='test1'

123 Query begin

123 Query select username, jid, nick, subscription, ask, askmessage, server, subscribe, type from rosterusers where username='test1' and jid='test4@192.168.1.250'

123 Query update rosterusers set username='test1', jid='test4@192.168.1.250', nick='', subscription='N', ask='I', askmessage='', server='N', subscribe='', type='item' where username='test1' and jid='test4@192.168.1.250'

123 Query insert into rosterusers(username, jid, nick, subscription, ask, askmessage, server, subscribe, type) values ('test1', 'test4@192.168.1.250', '', 'N', 'I', '', 'N', '', 'item')

123 Query commit

Memory footprint 
-----------------------

connecting 100 clients to ejabberd - no issue,
there are 9 instances running with around 70mb each.

Used this script to hit to server (Uses XMPPY )
-----------------------------------------

It assumes that we have test users already registered with username test1, test2.. and pass test1 and test2.  (ejabberdctl register command can be used to make such users)

from xmpp import *

clients = []
for i in range(100):
    clients.append(Client('192.168.1.250'))
for cl in clients:
    cl.connect(server=('192.168.1.250',5222))
for i in range(1,101):
    clients[i-1].auth('test%d'%i,'test%d'%i)

while True:
    for cl in clients:
        cl.sendPresence()

        cl.Process(2)

Sum good post
http://metajack.im/2008/08/27/migrating-to-ejabberd-the-gory-details/‎

Timezone and Confusion in Django

https://docs.djangoproject.com/en/dev/topics/i18n/timezones/

1) We use USE_TZ = True in our settings. It means, that Django will use Time zone aware datetime objects.
so, instead of doing this,

import datetimecur = datetime.datetime.now() # which doesnt give us tzinfo

we should use this -

import datetimefrom django.utils.timezone import utc

cur = datetime.datetime.now().replace(tzinfo=utc) # Note: This is for timezone aware not for local time

This will remove the warnings we usually see, "Datetimefield received a naive datetime."

2) For converting local time into current time zone,  according to one specified in settings file. We should use this

from django.utils import timezonetimezone.localtime(timezone.now())

Using Google Charts to show Data Point Values

Like most of us, in order to quickly use Google Charts Library, I copy pasted a simple code from https://code.google.com/apis/ajax/playground/?type=visualization#line_chart, adjusted to my use.

I wanted a Line Graph, with two data lines,  hours(1-24) on x axis and a number on y axis. This example was easy to customize , and most of my work was done(Please note- Most of it)

Now, I only wanted to show data values in the graph. As you can see, a tooltip pops up, when we hover on data points, I wanted tooltips or data values to show without the hover action.

The only way I could find was here - http://stackoverflow.com/questions/13449467/google-charts-api-always-show-the-data-point-values-in-graph

It says - data.addColumn({type: 'string', role: 'annotation'});


Now this is new, whats data? On going through the docs, I found that I have been using a method arraytoDataTable() [here] .This is a shortcut method to add data to graph. There is a DataTable class which has methods

• addColumn
• addRow
• addRows

See here  

this data in the above code, is the instance of the DataTable class. Now coming back to the same problem, in order to add annotation, we added the columns with role: annotation. Roles can be read here.

So now, I am able to see , the not so beautiful , annotations. 

What could be made better - Examples should be added for showing annotations. Currently there are none.

Compiling Ejabbered Module

While working on ejabbered, I came across a case where I had to compile a new module.

On googling and reading around stuff, I went through different posts -

• http://sacharya.com/writing-ejabberd-modules/
• http://anders.conbere.org/blog/2008/07/17/building_ejabberd_modules_-_part_2_-_generic_modules/
• http://stackoverflow.com/questions/8392326/intercept-login-logout-ejabberd
• http://uhlenheuer.net/posts/2013-01-16-writing_an_ejabberd_module.html

All of these posts were indeed very helpful to start but I faced some errors to compile , even after following the given steps.

My basic mod_hello.erl module,  had 

-module(mod_hello).
-behavior(gen_mod).

-export([
    start/2,
    stop/1
    ]).
start(_Host, _Opt) ->
        ?INFO_MSG("Loading module 'mod_hello' ", []).
stop(_Host) ->
        ok.

Using commands to compile this , 

erlc mod_hello.erl
erlc  -I {erlang_src_dir}/src -pa {erlang_src_dir}/src mod_hello.erl

 But nothing worked. I looked at the compiling commands that Ejabbered src used on compiling its erl modules. It was similiar to mine. Atlast on looking through the code, I found out the missing code..
the include commands.

So now, after addiing

-include("ejabberd.hrl").
-include("jlib.hrl").

Everything worked. Hooray..