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The Unweekly Review, 15/05/2011

Sun, 15 May 2011 10:17:00 -0700

Node.js becoming part of the stack?
Worth learning: GNU Coreutils z-commands
Opera Dragonfly 1.0 released - it's really really nice!
http://functionaljobs.com/ - the name says it all
Khan Academy - great approach to e-learning
Google accounts with multiple sessions - somehow I missed that before
Best practices for speeding up websites - from Yahoo
Google Storage
CDN JS - the missing CDN - interesting initiative
A nice Django cheatsheet
http://djangopackages.com/ - dozens of Django apps, not all are worth your attention - but still it's worth checking
Django, MySQL and transactions - watch out developer!

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The Unweekly Review

Sat, 23 Apr 2011 04:48:00 -0700

After two months of silence, I have some great stuff for you today:

http://habilis.net/cronic/ - a cure for Cron's chronic email problem, i.e. anti-spam for Cron
Reference on Named Pipes for those who didn't know them - http://en.wikipedia.org/wiki/Named_pipe
http://www.boxuk.com/blog/the-ultimate-website-launch-checklist
Google Python style guide - http://google-styleguide.googlecode.com/svn/trunk/pyguide.html
PEP on absolute vs relative imports in Python - very useful stuff - http://www.python.org/dev/peps/pep-0328/, http://docs.python.org/whatsnew/2.5.html#pep-328-absolute-and-relative-imports
How to get the user-selected part of the text in html input box? The solution: http://stackoverflow.com/questions/235411/is-there-an-internet-explorer-approved-substitute-for-selectionstart-and-selectio/4207763#4207763.
Tired of `ps aux|grep blah`? Check this out: http://en.wikipedia.org/wiki/Pgrep
A solution to a very tricky problem in Django, when saving a file causes UnicodeDecodeError on one computer but not on the other: http://docs.djangoproject.com/en/dev/howto/deployment/modpython/#if-you-get-a-unicodeencodeerror - it's valid even for mod_wsgi. Further reference: http://stackoverflow.com/questions/2457087/unicodedecodeerror-on-attempt-to-save-file-through-django-default-filebased-backe, http://code.djangoproject.com/ticket/11030#comment:5
Reference on tmpfs, i.e. in-memory file system, that can be used not only for keeping temporary files, but also for e.g. storing MySQL database files during unit testing. http://en.wikipedia.org/wiki/Tmpfs
Django trick to get all ForeignKey dependencies of some model instance: `my_model_instance.._meta.get_all_related_objects()`
Facebook shared the specs of their servers/hardware/data centers: http://opencompute.org/

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PyCuriosities, part 2

Sat, 19 Feb 2011 13:24:52 -0800

This is a follow-up to my first blog entry on curiosities in Python - PyCuriosities, part 1

Next set of tips:

Reversing a string or list (or more general - a sequence) is as simple as making a copy of it with negative increment: sequence[::-1] - which is equivalent to sequence[-1::-1] (see: Extended slices)
Built-in debugger (pdb) is great, but IPython-powered pdb (ipdb) is much better
Built-in SMTP module - smtplib - can raise not only its own SMTPException-s, but also socket.error-s. The same surprise can happen when using e.g. urllib2 - it can raise its own exceptions, httplib exceptions and socket.error-s.
In try..finally blocks, code in finally block is always executed. This can lead to errors if you put such try..finally block inside a function:
- >>> def f():
- >>> try:
- >>> return 1
- >>> finally:
- >>> return 2
- >>> f()
- 2
dict.setdefault(key, val) works like dict.get(key, val), except that in case key is not present in dict, it first sets dict[key] to val. As a result, it doesn't raise KeyError-s.
Collections.defaultdict is like dict.setdefault, but taken to the next level.
The Zip Trick (matrix transposition):
- >>> a = [1, 2, 3]
- >>> b = ['a', 'b', 'c']
- >>> x = zip(a, b)
- >>> x
- [(1, 'a'), (2, 'b'), (3, 'c')]
- >>> zip(*x)
- [(1, 2, 3), ('a', 'b', 'c')]
help('modules') lists all installed Python modules
You can create Python class manually using type(name, base_classes, class_members_dict). It can be used e.g. to create Django forms on the fly, like here.
Python supports so called metaclasses. You might never need them, but it's good to be aware of what they are:

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PyCuriosities, part 1

Sun, 13 Feb 2011 13:41:01 -0800

Here are some interesting, non-obvious things about Python language:

Logical operators and and or do not return boolean value - they return the last evaluated value. For example:
- ('a' and 'b') == 'b'
- ('' and 'b') == ''
- ('a' or 'b') == 'a'
- ('' or 'b') == 'b'
a == b is not the same as a is b. The former tests for equality and is just a syntactic sugar for a.__eq__(b) (well, not quite, but read this http://stackoverflow.com/questions/2281222/why-when-in-python-does-x-y-call-y-eq-x for details). The latter is a syntactic sugar for something like id(a) == id(b) (at least in 2.x line of CPython), i.e. it checks if both a and b point to the same object in memory.
Small integers are "cached" in 2.x line of CPython, for details read this: http://stackoverflow.com/questions/306313/python-is-operator-behaves-unexpectedly-with-integers
Python 2.x has a built-in profiler called Hotshot, which output file is compatible with KCacheGrind, a profile data visualization program
Default recursion limit in CPython 2.x is set to 1000 (http://docs.python.org/library/sys.html#sys.getrecursionlimit)
To check if given object is a string (str or unicode), just use isinstance(obj, basestring), where basestring is a base class for both str and unicode types
Python has a set of interesting string codecs. Some examples:
- s.encode('base64')
- s.encode('zip')
- s.encode('rot13')
- s.encode('string_escape')
If you need to embed a multi-line string in a nested block of code then you probably don't want to start each line of that string at the beginning of each code line - you rather prefer to keep it indented same as the surrounding code block. Still, you probably want it to print without the leading blanks. In such case textwrap.dedent is your friend

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The Unweekly Review

Tue, 25 Jan 2011 10:29:00 -0800

http://superuser.com/questions/231273/what-are-the-windows-a-and-b-drives-used-for - do you feel old now :-) ?
http://superuser.com/questions/10997/find-what-package-a-file-belongs-to-in-ubuntu-debian
http://headjs.com/ - the only script in your head! This looks really interesting, I'm planning to try it soon.
Varnish Cache - also something to try out eventually
DjangoCon EU - for those who missed it
less for gzipped files - very useful
"make any web page printer friendly"
Amazon Simple Email Service - new stuff from Amazon

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Slow urllib2

Tue, 25 Jan 2011 10:10:00 -0800

On different occasions I noticed that urllib2 (as well as lower-level httplib) was slow at opening remote pages, which was strange as usually GET was doing much better in terms of performance. A few days ago, being tired of this strange problem, I said "enough!" to myself.

A quick scan on what was going on behind the curtains revealed that it was the DNS lookup in Python library that was the bottleneck, and that the whole problem had been known for some time:

Fortunately, according to this message, it should be possible to fix the problem by messing with DNS configuration.

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Python's logging.TimedRotatingFileHandler quirk

Tue, 25 Jan 2011 09:49:00 -0800

If you're a logging module addict like me, you might want (at some point) to use its TimedRotatingFileHandler with when parameter set to "midnight". Unfortunately, this setup doesn't work in a general case, because the rollover happens only when log file is written to at a later date than it was opened!

Details of this problem are described here:

One of the possible solutions (described here), is to use logrotate for rolling logs over, and then make use of WatchedFileHandled (that works in a similar way to tail -F).

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Emacs (and Emacs config) update

Thu, 30 Dec 2010 15:53:00 -0800

Today I've upgraded my Emacs 23.1 - which is the default version in Ubuntu 10.04 - to the latest 23.2 release. The whole process has been very smooth, thanks to Michael Olson&Co who did all the hard work and shared the results here: https://launchpad.net/~ubuntu-elisp/+archive/ppa.

My overall impression is that the new Emacs seems to be "snappier" and have some additional small goodies here and there (or maybe they are just bug fixes?). It also has a bundled JavaScript major mode, which works great for my own scripts. Having such nice working environment, I've done my homework and updated my Emacs config in order to fix a few problems I've been living with for too long - here's the link: https://github.com/tomaszzielinski/My-Emacs-config/commit/85560cb7e8da2ba7fe7b827d0ea16606f50f7749

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The Weekly Review

Thu, 30 Dec 2010 04:27:00 -0800

Irregular as usual, but hot as always:

If you are using Xapian full-text search library in Ubuntu, and want to try its inspection tools (delve, quest: http://xapian.org/docs/admin_notes.html#inspecting-a-database), do not hesitate to apt-get install xapian-tools package;
Git-ize your bash prompt: http://hocuspokus.net/2009/07/add-git-and-svn-branch-to-bash-prompt/;
Soup recipe - take one python and one cucumber: http://lettuce.it/ https://github.com/heynemann/pyccuracy;
Are you a sociopath tired of delicious things? http://pinboard.in/ - antisocial bookmarking;
http://ubuntuforums.org/showthread.php?t=1315929 - when: import os; os.system("beep") stops working in Ubuntu 10.04

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Changing MySQL/InnoDb log buffer size (lifesaver hint)

Thu, 30 Dec 2010 04:12:00 -0800

The default configuration of MySQL is far from optimal. That's why one of my first steps after the installation is to tweak /etc/mysql/my.cnf.

You can find a nice reference configurations on a few pages around the web, and one of my favourite ones is: http://www.mysqlperformanceblog.com/2007/11/01/innodb-performance-optimization-basics/

One of the parameters they advise to tune is innodb_log_buffer_size. But there is a catch you have to be aware of - if you change that parameter's value, you also have to stop the MySQL service, remove InnoDb log files: http://www.mysqlperformanceblog.com/2007/11/01/innodb-performance-optimization-basics/#comment-364739, and then restart the service again.

Happy tuning!

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The Weekly Review

Sun, 12 Dec 2010 09:30:00 -0800

This time "weekly" is a wrong word, but let's uphold the tradition :-)

Browser inside browser: http://browserling.com/ - an easy way to check what Bill does to your pages
The game layer on top of the world: http://www.ted.com/talks/seth_priebatsch_the_game_layer_on_top_of_the_world.html - what might happen (in a good way) to our lives in the next decade
Capture your sessions: http://codebutler.com/firesheep
Chrome Web Store: https://chrome.google.com/webstore/ - how to convert a free weekend to a few bucks more :-)
Facebook Beta Tier: http://developers.facebook.com/blog/post/438 - do not let FB to break your build
HIDS: http://ubuntuforums.org/showthread.php?t=1477662 - how to protect your Ubuntu from a malicious software
Cross-browser Javascript caret position getter: http://stackoverflow.com/questions/235411/is-there-an-internet-explorer-approved-substitute-for-selectionstart-and-selectio/4207763#4207763; http://code.google.com/p/rangyinputs/

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10 tips on branding through social media for startups and small businesses

Tue, 16 Nov 2010 15:46:00 -0800

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From "it's just a C dialect" to really knowing it

Tue, 16 Nov 2010 15:35:42 -0800

I can use jQuery. I know how to debug problems with my JavaScript code. I know it's a prototype-based language. But I only understand it enough to be a decent web developer. And it was some time ago when JavaScript became a first-class citizen in the family of serious programming languages. That's why I've decided to gather a bunch of JS-related resources in one place and start learning it seriously. Here's the incomplete list assembled from my bookmarks: