David Janes' Code Weblog

February 2, 2012


python · admin · 7:49 pm ·


Times is a small, minimalistic, Python library for dealing with time conversions to and from timezones, for once and for all.

times tries to make working with times and timezones a little less of a clusterfuck and hopefully set a standard of some sort.

See my previous posts on working with pytz and dateutil (and also). I’m looking forward to trying out times.

December 7, 2011

Thoughts on Python 3

python · admin · 7:36 am ·

I’m learning a new language next year (suggestions welcome). I’ve totally ignored Python 3 and plan to continue doing so.

Read Armin Ronacher on “Thoughts on Python 3“.

Because as it stands, Python 3 is the XHTML of the programming language world. It’s incompatible to what it tries to replace but does not offer much besides being more “correct”.

Python 3 kills what makes Python great.

November 15, 2011

Python, Sqlite3, FTS3 & MacOSX

db,python,tips · admin · 8:49 am ·

If you can’t load FTS3 on a Mac, this post on StackOverflow tells you how to solve the problem.

The final bit of magic is in:

from pysqlite2 import dbapi2 as sqlite3

September 18, 2011

Adding alpha levels to images with PIL

code fragments,pil,python,tips · admin · 4:54 am ·

I recently was tasked by a client with replacing a number of images — PNGs with alpha levels, such that parts of the image were transparent — with new pictures. The issue was how to get the exact same alpha level holes in the new images.

Here’s how I did it. I renamed one of the original images “template.png” and assumed that all the source images will the exactly the same size as the template. I then wrote this Python script using the Python Imaging Library.

import sys
import os
import re
import Image

#   Get the template
itemplate = Image.open("template.png")
itemplate.getpixel(( 0, 0 ))
r, g, b, alpha = itemplate.split()

#   Get the JPGs - they must be exactly the same size
for in_file in os.listdir("."):
    if not in_file.endswith(".jpg"):

    isrc = Image.open(in_file)
    if isrc.size != itemplate.size:
    idst = isrc.convert("RGBA")

    idst.save(in_file[:-4] + ".png")

February 28, 2011

Foursquare, Python & OAuth2

authentication,code fragments,python · admin · 11:21 am ·

Foursquare has revved their API, but there’s no Python Library to support it. Here’s how to use it from Python

  1. Get OAuth info from foursquare — the callback URL does not matter _but_ you must record here. https://foursquare.com/oauth/register. Fill in the results into CLIENT_ID, CLIENT_SECRET and CALLBACK_URL
  2. Run this, enter the URL in browser, get code as FS_ACCESS_CODE, add back here
  3. Run this, fill in FS_ACCESS_TOKEN
  4. Run this, you’re authorized: enjoy!


  1. Python OAuth2 from here:  https://github.com/rodbegbie/python-oauth2
  2. This is entirely standing on the shoulder’s of Rod Begbie’s work.


import oauth2
import json
import pprint

OAUTH_BASE = "https://foursquare.com/oauth2/authenticate"



client = oauth2.Client2(CLIENT_ID, CLIENT_SECRET, OAUTH_BASE)

if not CLIENT_ID:
  print "=== Register your Foursquare data here"
  print "=== Copy back CLIENT_ID, CLIENT_SECRET and CALLBACK_URL here"
  print "https://foursquare.com/oauth/"
  headers, content = client.request("https://api.foursquare.com/v2/users/self", 
   access_token = FS_ACCESS_TOKEN)

    "headers" : headers,
    "content" : json.loads(content),
elif not FS_ACCESS_CODE:
  print "=== Enter this URL in your browser."
  print "=== Copy the CODE in the URL that results into FS_ACCESS_CODE"
  print client.authorization_url(redirect_uri = CALLBACK_URL, 
  print "=== Here is your Access Token"
  print "=== Copy into FS_ACCESS_TOKEN as start using Foursquare"
  print client.access_token(FS_ACCESS_CODE, redirect_uri= CALLBACK_URL,

December 24, 2010

Python recipe – sorting strings with numbers in them

code fragments,python · David Janes · 9:16 am ·

Here’s a quick Christmas Eve recipe for sorting lists of strings that have numbers in them at some place.

import re
import string

numeric_rex = re.compile('(\d+)')

def numeric_sorter(a, b):
    av = filter(None, numeric_rex.split(a))
    bv = filter(None, numeric_rex.split(b))

    while av and bv:
        af = av.pop(0)
        bf = bv.pop(0)

        if af[0] in string.digits and bf[0] in string.digits:
            r = cmp(int(af), int(bf))
            r = cmp(af, bf)

        if r != 0:
            return  r

    if av:
        return  1
    elif bv:
        return  -1
        return  0

Here’s an example of it being used:

>>> items = [ "Item1", "Item10", "Item", "Item9", "Item100", "ItemLogo", ]
>>> items.sort()
>>> pprint.pprint(items)
['Item', 'Item1', 'Item10', 'Item100', 'Item9', 'ItemLogo']
>>> items.sort(numeric_sorter)
>>> pprint.pprint(items)
['Item', 'Item1', 'Item9', 'Item10', 'Item100', 'ItemLogo']

January 11, 2010

How to add XCode '#pragma mark'-like sections for Python code

python,tips · David Janes · 7:43 am ·

Just add in your Python comments:

# MARK: comment
# TODO: comment
# FIXME: comment
# !!!: comment
# ???: comment

From here.

November 16, 2009

PIL, libjpeg, jpeg and Mac OS/X Snow Leopard

macintosh,python,tips · David Janes · 7:47 am ·

If you want to the use the Python Imaging Library on Mac OS/X Snow Leopard, these instructions appear to be the best way to to get libjpeg installed:

1. Download the source from http://libjpeg.sourceforge.net/

2. Extract, configure, make:

tar zxvf jpegsrc.v6b.tar.gz
cd jpeg-6b
cp /usr/share/libtool/config/config.sub .
cp /usr/share/libtool/config/config.guess .
./configure --enable-shared --enable-static

3. You may need to create the following directories:

sudo mkdir -p /usr/local/include
sudo mkdir -p /usr/local/lib
sudo mkdir -p /usr/local/man/man1

4. Now you can install it as usual.

sudo make install

I used to use Fink on Leopard, but it didn’t seem to work to well this time. If you’ve previously made an attempt at installing PIL, make sure to rm -rf build.

Django 1.1 and ImageField

code fragments,django,python,tips · David Janes · 7:42 am ·

Having recently upgraded to Django 1.1, I suddenly started getting the error messages that look like:

  File "/Library/Python/2.6/site-packages/django/db/models/fields/related.py", line 257, in __get__
    rel_obj = QuerySet(self.field.rel.to).get(**params)
  File "/Library/Python/2.6/site-packages/django/db/models/query.py", line 300, in get
    num = len(clone)
  File "/Library/Python/2.6/site-packages/django/db/models/query.py", line 81, in __len__
    self._result_cache = list(self.iterator())
  File "/Library/Python/2.6/site-packages/django/db/models/query.py", line 251, in iterator
    obj = self.model(*row[index_start:aggregate_start])
  File "/Library/Python/2.6/site-packages/django/db/models/base.py", line 324, in __init__
    signals.post_init.send(sender=self.__class__, instance=self)
  File "/Library/Python/2.6/site-packages/django/dispatch/dispatcher.py", line 166, in send
    response = receiver(signal=self, sender=sender, **named)
  File "/Library/Python/2.6/site-packages/django/db/models/fields/files.py", line 368, in update_dimension_fields
    (self.width_field and not getattr(instance, self.width_field))
AttributeError: 'Icon' object has no attribute 'width'

The issue turns out to be that you can’t just define the ImageField in your model, you also have to explicitly define the fields that will store the width and height fields for the image field. The sql generation tools for Django don’t do it for you.

For various reasons, I can’t do that this at this moment so I made the following I hack which I strongly recommend you don’t use (for efficiency reasons, as with this the height & width have to be computed every time you access the image). This is added to site-packages/django/db/models/fields around line 367.

if self.width_field and not hasattr(instance, self.width_field):
     dimension_fields_filled = False
     dimension_fields_filled = not(
          (self.width_field and not getattr(instance, self.width_field))
          or (self.height_field and not getattr(instance, self.height_field))

The proper solutions probably involve:

  • not adding the hack above and explicitly adding the fields, as per here
  • updating the documentation (here and here) to say “you also have to add the fields to the DB”
  • making syncdb/sql automatically generate the width & height fields

October 24, 2009

Fizz Buzz in one line of Python

code fragments,python · David Janes · 5:58 am ·

Since Libin points to “Fizz Buzz” in one line of Ruby, I feel it’s only fair to do it in one line of Python:

print [ not i % 15 and "Fizz Buzz" or not i % 5 and "Buzz" or not i % 3 and "Fizz" or i for i in xrange(1, 101) ]

My preference is to really have a few more brackets in there, for clarity but apparently terseness is considered a virtue in and off itself sometimes. There’s other implementations of this in one line of Python:

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