Python, Virtualenv and Docker

Unsurprisingly I use some very popular Scientific Python packages like Numpy, Scipy and Scikit Learn. These packages don't get on that well with virtualenv and pip as they take a lot of external dependencies to build. These dependencies can be optional libraries like libblas and libatlas which if present will make Numpy run faster, or required dependencies like a fortran compiler.

Back in the good old days you wouldn't pin all your dependency versions down and you'd end up with a precarious mix of apt-get installed and pip installed packages. Working with other developers, especially on different operating system update schedules could be a pain. It was time to update your project when it breaks because of a dependency upgraded by the operating system.

Does virtualenv fully solve this? No, not when you have hard requirements on the binaries that must be installed at a system level.

Docker being at a lower level gives you much more control without adding too much extra complexity. For several projects now I've created a standard operating environment (SOE) docker image and we test and deploy our code running inside this or a derivative of this container.

As a public example I've created a base container for Docker which includes all of the required binaries to build numpy, scipy and cryptography from source - find it on docker hub, or pull it straight to your computer:

    docker pull hardbyte/python3

Bluetooth with Python 3.3

Since about version 3.3 Python supports Bluetooth sockets natively. To put this to the test I got hold of an iRacer from sparkfun . To send to New Zealand the cost was $60. The toy has an on-board Bluetooth radio that supports the RFCOMM transport protocol. The drive protocol is dead easy, you send single byte instructions when a direction or speed change is required. The bytes are broken into two nibbles: 0xXY where X is the direction and Y is the speed. For example the byte 0x16 means forwards at mid-speed. I was surprised to note the car continues carrying out the last given demand! I let pairing get dealt with by the operating system. The code to create a Car object that is drivable over Bluetooth is very straight forward in pure Python: import socket import time class BluetoothCar : def __init__ ( self , mac_address = "00:12:05:09:98:36" ): self . socket = socket . socket ( socket . AF_BLUETOOTH , socket . SOCK_STREAM , socket .

Matplotlib in Django

The official django tutorial is very good, it stops short of displaying data with matplotlib - which could be very handy for dsp or automated testing. This is an extension to the tutorial. So first you must do the official tutorial! Complete the tutorial (as of writing this up to part 4). Adding an image to a view To start with we will take a static image from the hard drive and display it on the polls index page. Usually if it really is a static image this would be managed by the webserver eg apache. For introduction purposes we will get django to serve the static image. To do this we first need to change the template. Change the template At the moment poll_list.html probably looks something like this: <h1>Django test app - Polls</h1> {% if object_list %} <ul> {% for object in object_list %} <li><a href="/polls/{{object.id}}">{{ object.question }}</a></li> {% endfor %} </ul> {% else %} <p>No polls

Python and Gmail with IMAP

Today I had to automatically access my Gmail inbox from Python. I needed the ability to get an unread email count, the subjects of those unread emails and then download them. I found a Gmail.py library on sourceforge, but it actually opened the normal gmail webpage and site scraped the info. I wanted something much faster, luckily gmail can now be accessed with both pop and imap. After a tiny amount of research I decided imap was the better albiet slightly more difficult protocol. Enabling imap in gmail is straight forward, it was under labs. The address for gmail's imap server is: imap.gmail.com:993 Python has a library module called imaplib , we will make heavy use of that to access our emails. I'm going to assume that we have already defined two globals - username and password. To connect and login to the gmail server and select the inbox we can do: import imaplib imap_server = imaplib . IMAP4_SSL ( "imap.gmail.com" , 993 ) imap_server . login ( use

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