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Archive for the ‘Python’ Category

uvloop – Python replacement for asyncio event loop

Posted by Venkatt Guhesan on April 1, 2017

uvloop is a fast, drop-in replacement of the built-in asyncio event loop. uvloop is implemented in Cython and uses libuv under the hood.

Benefits: uvloop makes asyncio 2-4x faster.
Cons: uvloop is available from PyPI but it requires Python 3.5. (The reason for this is asyncio was introduced in Python 3.4 and above.) Unless your project is based on Python 3.4+ – you may not be able to leverage this library.
Alternatives: For the folks that are using Python 2.7 (including me), if you search for “asyncio alternatives” you will quickly come across the Trollius project. But unfortunately this project is no longer under development. Eventually, you will arrive a discussion on GIL and multi-cores like this article. Yes, the Python community is torn between 2.7 and 3.x. Your best bet at this point of time for Python 2.7 users is to leverage Tornado’s async facility using Callbacks, futures, promises and deferred.  A hybrid but elegant alternative is to use Cyclone (Takes Tornado’s elegance and applies it to Twisted library).

Read more about uvloop here:

To learn more about the other libraries mentioned here refer to this blog article:


Today’s inspirational quote:
  • Letting go is a necessary, if sometimes heart-wrenching gateway to genuine transformation.

Posted in Python, Uncategorized | Tagged: , | Leave a Comment »

Uninstall python eggs that you installed using

Posted by Venkatt Guhesan on September 30, 2016

python_logoIn Python, most libraries are available using the pip install process. But for cases, where you are distributing code to be installed in customer sites where you may or may not have a internet connection to the pip libraries, you resort to the legacy process.

When you install using the process, the copies it’s collection of python files to the site-packages folder for your python virtual-environment. On a CentOS, this might be a location under (/usr/lib/python2.7/site-packages/) directory. This may also write it’s files to other locations such as config files and resource files.

Once installed and if you decide you want to uninstall or upgrade the package or egg, it’s hard to identify all the files that this egg touched. Within the process there are some other options that can help you in identifying the python files that are placed in these locations. Here is an example of how you can identify the files and remove the files before upgrading.

# To note down the list of files that are installed
python install --record egg-files.txt
# To remove those files you can do the following using the egg-files.txt
cat egg-files.txt | xargs rm -rf
# This would remove the individual files but will leave the "<project>.egg-info" directory and other artifacts under site-packages. 
# You can remove the package directories manually

On the other hand, if you have access to pip then you can leverage “pip freeze” options (read more here) along with “pip uninstall” option (read more here).


Posted in Python | Tagged: , , | Leave a Comment »

Python pycharm – configuring remote interpreters from Windows to Linux

Posted by Venkatt Guhesan on April 20, 2012

If you are an avid Python developer, you may all be excited about the new features available in the Pycharm 2.5 release, especially the remote interpreters, virtualenv and support. You can read more about the new exciting features here.

But as I started to tinker with the “remote interpreter” feature – I stumbled upon some challenges and I thought I’d document them for other PyCharm users who might benefit from this blog entry.

Let’s get right into the issue:

My Setup:

I have a Windows 7 host where I do most of my development. I develop software for a Linux based system and most of the Python libraries that I need to work from third-party vendors are only available for Linux. And so my PyCharm IDE runs on Windows and I have a VirtualBox instance of CentOS linux running within my host machine accessible via a Virtual Box – Bridged Adapter. This Linux could also be running in a separate  physical host accessible via TCP-IP. Now that we have a good idea about my development environment, let’s go over why I want to use the “remote interpreters” feature.

Remote Interpreters

This feature allows you to connect with a Python environment and all’s of it’s SITE_PACKAGES available on the remote machine as if you were running it locally on your native PC. Furthermore, you can perform step-through of your code right from your development platform as if you ran the IDE right within the Linux machine. (Please note that this feature can then lend itself to running the Linux server as a terminal without a GUI/Windows Manager like KDE/Gnome). This will simplify your footprint on the server side.


When you run the interpreter, you will run into issues such as “No such file or directory.” That’s because when you execute a file natively in Windows under c:\temp\ – the “remote interpreter” is now looking for a file under that same path in the remote server under Linux. To avoid this issue, here’s the solution I have engaged.

  1. Share my c:\projects\MyProject to myself so that I can map a new drive under Windows such as “K:\MyProjects”.
  2. Shared a “Machine Folder” to my Virtual machine. If you have a remote host, then either setup a GIT push scheme or a SFTP from your Windows to this remote server. See image below for illustration.
    Virtual Box - Machine Target
  3. At this time, My “c:\projects” folder is shared to the Linux environment as “/media/sf_K_DRIVE/” and “auto-mounted”. (I have also added my user-id to the “vboxsf” group because of permissions. But that’s another blog…)
  4. Now every modification of my Python files in my “K:\MyProject”, is exactly the same on the Linux virtual-box.
  5. The first setting to change is the “Line Seperator” (unless you want to execute Dos2Unix each time you run the file on Linux). This can be done under “Code Style” in PyCharm Settings. See image below:PyCharm Settings Line Seperator
  6. Next, configure the “Remote Python Interpreter”. See screenshot below:PyCharm - Configure Remote Interpreter
  7. In the previous step, when you choose a path on the Linux server for the “PyCharm helpers”, PyCharm pushes via SSH a set of libraries and software that helps with the remote debugging and scaffolding.
  8. The next step is to Run (or Debug) your code. See the screenshot below that shows the details of the “Run/Debug Configuration” screen. The important parts are “Working Directory” and “Path Mappings”. This is the trick that allows you to map your Windows Path to an equivalent Linux Path.PyCharm - Run/Debug Configuration Screen
  9. Now run (or debug) away your code as if it was running locally on your native Windows development platform.

That should get the job done.

Update on May 18th, 2012

#This shows you an example of how you would invoke a Python UnitTest via remote-interpreter to another script located in the same folder.

#Invoked from
scriptName = ""
# BASE_PATH is the absolute path of ../.. relative to this script location
BASE_PATH = reduce(lambda l,r: l + os.path.sep + r, os.path.dirname( os.path.realpath( __file__ ) ).split( os.path.sep ) )
#print BASE_PATH
# add ../../scripts (relative to the file (!) and not to the CWD)
NEWSCRIPTPATH = os.path.join( BASE_PATH, scriptName )

#Further down in code…
p1 = os.popen("%s" % self.NEWSCRIPTPATH, "w")

For early Pythons…

#If you are using Python 2.6.6 (not Python 2.7+)
scriptLocation = ""
scriptLocation = os.path.join( os.path.dirname( os.path.realpath( __file__ ) ), scriptLocation )
print scriptLocation

#Further down in code…
p1 = os.popen("%s" % self.NEWSCRIPTPATH, "w")

Posted in Programming, PyCharm, Python, Technology | Tagged: , , , , , , , , , , , , | 6 Comments »

Configure static resources in Django – Python

Posted by Venkatt Guhesan on March 1, 2012

Working on a Django project, one of the first things that one would encounter is configuring Django for static resources such as “css”, “images”, “jpeg” and “js”. In looking at the “StaticResources” link that’s part of the Django documentation, it’s a bit cryptic for someone who’s starting out in Django and Python. So here’s a step-by-step on two ways to configure your static-resources in a Django project.

This method is described in the Django documentation and is probably the preferred approach.

1. Edit “” under your Django project and define the following variables:

STATIC_URL = '/s/'

2. Edit “” and add the following:

from spog import settings
if settings.DEBUG:
    urlpatterns += patterns('',
        (r'^s/(?P<path>.*)$', 'django.views.static.serve',
           {'document_root': settings.STATIC_ROOT}),

Notice the extra comma at the end. That’s very important!

3. Edit your html file, in this example index.html

<link rel="stylesheet" type="text/css" href="/s/css/grid960.css"/>

4. Copy your resources to “C:\Projects\mydjangoproject\static\css\grid960.css”.

5. python runserver 8080

6. Open browser and visit “http://localhost:8080/%5BYOUR_PAGE%5D&#8221;.

If you notice the step-2 syntax, it is wrapped inside a “if settings.DEBUG” if-block. This variable will be false when you deploy to a production environment where you may have something like an Apache Web server serving all your static resources. So when you move to production, you can push all your static resources to be outside the project.

Posted in Django, Python | Tagged: , , , , | Leave a Comment »

How-To Install mod_python and the compile error – apxs:Error: Command failed with rc=65536

Posted by Venkatt Guhesan on December 28, 2011

Below are my steps to installing mod_python under Apache HTTPD in CentOS 6.2.

Download mod_python-3.3.1.tgz or a later version of mod_python available here:

curl -O
tar zxvf mod_python-3.3.1.tgz
cd mod_python-3.3.1

You may encounter the following error at this point:
apxs:Error: Command failed with rc=65536

If so… no worries…

This bug has been addressed here:

Download the patch and (if you can figure out how to patch like I did, I manually opened the file and examined the contents:

diff -rNu mod_python-3.3.1/src/connobject.c mod_python-3.3.1-atomix/src/connobject.c
--- mod_python-3.3.1/src/connobject.c 2006-12-03 05:36:37.000000000 +0100
+++ mod_python-3.3.1-atomix/src/connobject.c 2008-10-02 14:10:02.000000000 +0200
@@ -139,7 +139,7 @@
bytes_read = 0;

while ((bytes_read < len || len == 0) &&
+ !(b == APR_BRIGADE_SENTINEL(bb) ||

const char *data;

Based on the file contents… Edit the following file below the unzipped folder (/mod_python-3.3.1/src/connobject.c)

Change line 142 from

Save the file. And then run “make” again.

This time you should see no errors. The last step is to run “make install” and you’re all set.

Now don’t forget to edit your main config and add
LoadModule python_module /usr/lib64/httpd/modules/
and if your configuration uses ClearModuleList, then also
AddModule mod_python.c

Next, Configure mod_python to work with Apache

Edit your httpd.conf (/etc/httpd/conf/httpd.conf), add:

LoadModule python_module /usr/lib64/httpd/modules/

#Under the AddHandler section

<Directory /var/www/html>
    AddHandler mod_python .py
    PythonHandler myscript
    PythonDebug On

To learn what the “AddHandler” does go here:

Stop and Start Apache HTTPD (/etc/init.d/httpd restart)

You’re all set.

To verify, create a file in your DocumentRoot (/var/www/html)


from mod_python import apache

def handler(req):

    req.content_type = "text/plain"
    req.write("Hello World from Apache HTTPD!")

    return apache.OK

As a last step, goto http://<your_ip&gt;:<your_port_80>/

You should see, “Hello World from Apache HTTPD!”. Notice that I didn’t goto “”. And I have pointed to “myscript” in the AddHandler parameter. This “” acts like the Controller in a MVC framework. So if you were installing an application like Django… then Django will act as the gatekeeper passing requests back and forth.

To learn more about the handler, go here:

or here’s an excerpt from that site:

Note that according to the configuration written above, you can also point your browser to any URL ending in .py in the test directory. You can for example point your browser to /test/ and it will be handled by That’s because you explicitely set the handler to always be mptest, whatever the requested file was. If you want to have many handler files named, and so on, and have them accessible on /test/, /test/, etc., then you have to use a higher level handler system such as the mod_python publisher (see 3.1), mpservlets or Vampire. Those are just special mod_python handler that know how to map requests to a dynamically loaded handler.

After writing this blog, I noticed that some users may prefer a PHP like feel. This can be done by adding a “Publisher Handler” (PSP).

Edit your httpd.conf (/etc/httpd/conf/httpd.conf), add:

LoadModule python_module /usr/lib64/httpd/modules/

#Change AddHandler to the following

<Directory /var/www/html>
   AddHandler mod_python .psp .psp_
   PythonHandler mod_python.psp
   PythonDebug On

Stop and start httpd (/etc/init.d/httpd restart).

Now create a file “test.psp” under DocumentRoot (/var/www/html)

import time
weekday = time.strftime('%A', time.localtime(time.time()))
message = 'Today is %s.' % weekday
<h2><%= message %></h2>

When you visit http://<your_ip&gt;:<your_port_80>/test.psp

You should see “Today is —” message.

You can learn more about the PSP handler here:


Posted in mod_python, Python | Tagged: , , | Leave a Comment »

How to upgrade to Python 2.7 on CentOS

Posted by Venkatt Guhesan on December 28, 2011

If you tried upgrading to Python 2.7 on CentOS, you will quickly find out that the RPM’s don’t exist for this in the repos. So here’s a short summary of what I did to upgrade my Python to 2.7 on CentOS.

Based on a few Google searches… I discovered that a few dependent packages are required before you try upgrading to Python 2.7.

yum -y groupinstall 'Development Tools'
yum -y install openssl-devel* ncurses-devel* zlib*.x86_64</pre>
yum -y install bzip2 bzip2-devel bzip2-libs

Next download the latest tar/gzip/tgz available here:

#Download the latest available at this time
curl -O
#Unzip/expand file
tar xfz Python-2.7.tgz
#Change Directory to the unzipped folder
cd Python-2.7
#read README file or you can follow the lines below
#you could also run configure with threads and shared enabled
#./configure --prefix=/opt/python2.7 --with-threads --enable-shared
make install
# Exit from your shell and open a new shell/SSH session
# Use the command below to display which path of python is currently active
which python
#To verify if the install succeeded
python -V
#Use UPPERCASE 'V' - not lower-case.
#Output will be "Python 2.7"
#Sometimes you may need to exit out of your shell
#and them come back in to see the version changes.
#So best exit your current shell prompt and reopen
#a new before checking the version.

You’re all set. You’ve just upgraded to Python 2.7.

The next logical step that you need to perform is to install the setup tools that allows you to install modules. (Please note that setuptools is not available for Python 3.0+, instead use Distrubute available here –

Download the latest setuptools for your version of Python (2.7 in this case) from here:

curl -O

chmod 775 setuptools-0.6c11-py2.7.egg

sh setuptools-0.6c11-py2.7.egg

#This should install the egg here: /usr/local/lib/python2.7/site-packages/

Next you want to install “PIP”, this enables the download and install of modules in Python:

$ curl -O
$ tar xvfz pip-1.0.tar.gz
$ cd pip-1.0
$ python install # may need to be root</pre>

Now you’re all set. Suppose you wanted to install a module called ‘simplejson’.

You can now do this using command syntax like this:

pip install simplejson


Posted in Python | Tagged: , , , | 10 Comments »