22 Jan 10 Testing Your First Django App
Dougal Matthews wrote a great blog post entitled “Testing Your First Django App“. This is something that I have been meaning to do for a long time now, but didn’t know how to get started. Much to my surprise (I guess I shouldn’t be), Python supports the xUnit style of testing via the standard library package unittest. Since we are now using CxxTest at work, this is quite familiar to me now. Dougal’s blog entry shows some nice ways of testing Django web applications without using a server by mocking up requests and examining responses from your view functions. Very cool!
31 Dec 09 Python and SSH
I was fooling around with my webcam, and I got to wondering if I could write a small Python script to upload a snapshot to my webserver periodically. Since I was planning on uploading a new snapshot every ten minutes or so, I’d rather use SFTP to avoid sending my login and password unencrypted so frequently. I had already used FTP in Python before in a backup script, but I didn’t know if the Python standard library had a solution for SSH. After a bit of Googling, I discovered the 3rd party Python module Paramiko (the name is a combination of the Esperanto words for “paranoid” and “friend” — I love that), which allows you to do all kinds of SSH2 operations, including SFTP. Paramiko is extremely well documented (thank-you!) and I had no problems at all using it to accomplish my task. I also found this great introductory article by Python core developer Jesse Noller that was helpful in getting up to speed on it quickly.
Since I was using my webcam from Windows XP, I decided to write my script under the new 1.7.1 version of Cygwin that came out recently. You’ll need to get both the Paramiko package and the python-crypto package.
Happy New Year everyone!
13 Dec 09 Python Subprocess Popen and Windows
I was writing a Python script to automate some Subversion-related tasks at work last week on Windows. The Python code was calling the Subversion command-line client applications using the Python subprocess module. I don’t know why exactly, but I had passed in the parameter shell=True to the subprocess.Popen function. I probably did this because I saw a lot of examples on the web, and you know, monkey-see, monkey-do. In hindsight, these examples were probably for Unix. It turned out that this caused a lot of problems. The Subversion clients started complaining when handed filenames that contained “special” characters like ampersands. And when they got to the files that had both ampersands and spaces, all kinds of crazy errors were produced. I was pulling my hair out, trying to escape the special characters and/or use quotes around the filename, but I could not come up with a combination that would work for all the different filenames the script encountered. Finally, as I stared at the code, I somehow got the idea to try switching that shell=True to shell=False. Suddenly, everything worked perfectly. I undid all the escaping and quoting and everything worked as expected.
So I’m not sure what shell=True does on Windows, and it certainly isn’t documented. I do not recommend using it unless you know what is happening in the implementation. Interestingly, shell=False is the default. I should have left it that way. 
Tags: python, subprocess, svn, windows
30 Nov 09 Using the Python Shell in Vi Mode
The Python shell is an invaluable tool for trying things out and experimenting with the language. Wouldn’t it be great if you could use the Python shell in Vi mode? Much to my surprise, it turns out you can.
Python leverages the GNU Readline Library in its shell code. The Readline library is used in a number of open source projects, notably the BASH shell. The Readline library looks for a configuration file at startup in a number of places. On Unix-like operating systems, the configuration file can be found at ~/.inputrc and falls back to /etc/inputrc.
One line is all you need in your ~/.inputrc file:
set editing-mode vi
Unfortunately I don’t know how to make this work under Windows.
18 Nov 09 Vim: Different Settings For Different File Types
Old habits die hard. I have been using 3 space indents for C and C++ code for as long as I have been a programmer. A little over a year ago I dove head-first into Python, and eventually discovered PEP 8. PEP 8 is basically the style guide for the Python community. I read it with great interest and took just about everything to heart, except for the recommended 4-space indents. I just could not shake my old habit.
Eventually as I got more and more excited about Python I decided to wholly embrace the customs of the community. But how could I easily tell my favorite editor Vim to use 4-space indents for just Python code? I still do a lot of C++ at work, and I still like 3-space indents in other file types.
My first attempt was to use a Vim modeline embedded right in my source files. At the bottom of my Python files I placed this line:
# vim: set sw=4 ts=4:
When Vim first opens a file, it scans the first and last few lines in the file, looking for modelines, and will use the settings just for that file.
This obviously worked, but soon I found it ugly and distracting to have that at the bottom of each file. And sometimes I would forget to put it there, and not realize it until a bunch of code had been written.
It turns out there is a far easier way, but it took some digging to discover. Vim has a very elaborate system of determing file types. If you peek into your Vim installation directory, you’ll see a ftplugin directory. This directory is full of little files that get executed once the type of a file has been determined. Some people on the Web suggest that you should modify these files directly. Thus I could modify the ftplugin/python.vim file, and place my tabstop and shiftwidth settings in there. But you would be modifying a Vim file, and your changes would get lost the next time you upgrade Vim.
There is a much better solution. After Vim executes the python.vim file in the ftplugins directory, it looks for a file called ~/.vim/after/ftplugin/python.vim (on Unix; on Windows I’ve had luck with C:\Progam Files\Vim\vimfiles\after\ftplugin\python.vim). If this file exists, it will be executed after the “official” python.vim file.
Inside your personal python.vim file, the documentation says to use the “setlocal” instead of “set” command. Thus, my file looks like:
setlocal tabstop=4 setlocal shiftwidth=4
Although to be honest, I’ve used the regular set for some time (by accident) without seeing any strange effects.
Happy Vimming!
Tags: vim
24 Sep 09 I <3 Vim
I love the text editor Vim. I started using Vi because I really didn’t know any better around 1988 when I was first teaching myself C on my trusty Amiga 500. Not long after that I discovered Vim which sported many improvements over the venerable Vi. Sometime around 1993-1994 I started hacking Vim. I added a complete ARexx port to Vim so that you could script it. Alas, a new version of Vim came out right after I finished, and author Bram Moolenaar had changed the code so much I felt it was impossible to merge my changes into the new version. This was when I was a young pup programmer, and I was unfamiliar with revision control and difference/merging tools. I had fun doing it anyway, so I just chalked it up to experience.
I have used Vim on every programming task at every job I’ve had. I’m constantly learning new things about it, and the commands and keystrokes are now part of my DNA. I don’t even think how to execute commands anymore and I am often hard pressed to recall them to others learning Vim. I have to sit at a keyboard with Vim running in order to understand what my fingers are doing.
A while back, I discovered the auto-complete feature, where you type Ctrl-n in insert mode and Vim will attempt to complete the word you are typing based on all the words in all buffers and how frequently they occur. This is incredibly handy when programming to quickly pound out those function and variable names. I used “imap <S-Tab> <C-n>” in my .vimrc file to map this to shift-tab, which I felt was more convenient.
I also picked up a really handy way to cycle through all your buffers. I used the tab and shift-tab mapping mentioned in that Vim tip. Combine that with Vim’s tab feature I can very easily find the file I am looking for.
And finally I had another big “wow, Vim can do that?” moment just last week. Since version 7, Vim has sported an “omni-complete” framework. Basically it is an architecture for people to hang code completion routines into Vim. In fact, right out of the box, Vim 7 has support for Javascript, CSS, and yes, even Python! Python completion is only available if you are using a version of Vim that has been compiled with Python support (e.g. on Ubuntu). Imagine my shock when I was editing a CSS file and I typed “display:” and then hit Ctrl-X Ctrl-O for the first time and a drop down list of all the possible values (inline, block, none, etc) appeared! No more hunting for that w3schools website. And the Python support is just as handy. Type “os.path.” followed by Ctrl-X Ctrl-O and you can see all the entities and function in the os.path module. I had no idea!
So all of this reminds me it is time to once again donate to the Vim project. Thanks Bram for all your amazing work you do on this invaluable tool.
P.S. I have no interest in the great editor holy war. Use a tool that you find intuitive and useful and learn it, back to front. I’m sure there is nothing wrong with other popular editors. But for me, Vim is it. I can’t imagine how many hours of productivity it has given me over the years.
Tags: vim
