Computing permutations with a recursive generator expression

#!/usr/bin/python2.5
def permute(li):
    """Generate all permutations of a sequence
    >>> for i in permute([1,2,3]): print i
    (1, 2, 3)
    (1, 3, 2)
    (2, 1, 3)
    (2, 3, 1)
    (3, 1, 2)
    (3, 2, 1)"""
    return ((i,)+j for i in li for j in (permute([k for k in li if k is not i])
                                         if len(li) > 1 else [()] ) )

import doctest
doctest.testmod(verbose=True)

LCARS 4.2 released

Here is another photo and a screenshot of our new theme, Okuda:

 

The changelog has details on what else is new. To install or upgrade, just use this .install file. After installing, select a theme and a background and then reboot for everything to be properly reloaded.

The install process is unfortunately rather slow, usually taking between 1 and 3 minutes, due to the numerous cache files which must be updated post-install. Starting with this release, the themes’ postinst scripts now run gtk-update-icon-cache on the icon themes’ directories, and lcars-extras runs it on the hicolor icon theme in postinst and postrm. The Okuda theme includes a font, so it runs fc-cache. And, as before, all of the themes run hildon-theme-cacher (which is the slowest of the three types of cache). I’m not sure why hildon-theme-cacher needs to be run on the device; it seems like it would make more sense (and be quicker for users) to pre-generate those gtkrc cache files as part of the themes’ build process. Oh well.

Enjoy the new themes, and please let us know if you make modified versions! :)

Preview of our new Maemo theme

Ian and I have been working on a new release of our LCARS packages, featuring a number of bug fixes as well as a new theme called “Okuda”:

If all goes well, we should be ready to release this within the next 48 hours. All four of our themes now include icon templates, which we’re slicing with hildon-theme-slicer (the same way that the main theme template is processed). This is what the icon template for the Okuda theme looks like:

Anyone else wishing to create a hildon-theme-tools (and ThemeMaker) compatible layout definition might find this Python script helpful:

#!/usr/bin/python2.5
"""Generate a hildon-theme-tools layout from variously sized images.
Edit script to specify desired margin, width, and origin (dx,dy).
usage: hildon-theme-layout-grid-generator.py `find icons|sort|grep png`
"""

__author__ = "Leif Ryge <leif @synthesize.us>"
__license__ = "no rights reserved / public domain"

from sys import argv
from PIL import Image

margin, width, dx,dy = 10, 600, 0,0 # margin, output width, starting coords
sizes = {}

for f in argv[1:]: sizes.setdefault(Image.open(f).size,[]).append(f)

print "[Main]\nTemplateWidth=%s\nTemplateHeight=%s\n\n[Elements]" % (width, \
    sum((h+margin)*(len(sizes[w,h])/(width/(w+margin))+1) for w,h in sizes) )

for w,h in sorted(sizes):
    column = width / (w+margin)
    row = 1 + len(sizes[w,h]) / column
    print "# %s images are %sx%s (%sx%s grid)" % (len(sizes[w,h]),w,h,column,row)
    for i, f in enumerate(sizes[w,h]):
        print "%s=%s,%s,%s,%s" % (f, dx+(i%column)*(w+margin),
                                     dy+(i/column)*(h+margin),w,h)
    dy = dy+row*(h+margin)

The actual template can then be created from existing images using Nokia’s hildon-theme-regenerator tool.

Memoization in one line

The memoization decorator in the Python Decorator Library has served me well, but, after reading stupid lambda tricks, I started thinking about how it could be reduced to a single expression. This is the result:

memoize = lambda f: (lambda d={}: lambda *a: d.setdefault(a, a in d or f(*a)))()

Unlike the original, mine doesn’t catch the case of the memoized function being called with unhashable (mutable) arguments. It doesn’t seem like that is a likely scenario, though.

Here is another version which also works with functions taking named arguments:

memo_with_named_args = lambda f: (lambda d={}: lambda *a,**kw: \
    (lambda *k: d.setdefault(k, k in d or f(*a,**kw)))(tuple(kw.items()),a) )()