Showing posts from 2008

One of the things I like the least about my real job, and much of the contract work that I do is that i'm usually the only programmer working on each task. So, it's been very fun to work on a project with Josh Livni (His writeup). We got together one afternoon, and by the time we left, we had a reasonable start of what we call landsummary, we've since put in a fair bit of work sprinkled here and there. Josh set up an AWS server--it's nice for me to have fewer sys-admin duties too.
What's actually on display is fairly modest. What it does is takes a user-drawn square, circle, or arbitrary polygon, and uses that to summarize the NLCD dataset along with some census data. The things that make it more than lame are that it's very fast, it can easily be extended to summarize any raster dataset, and we have a sorta cool API (not documented) which allows us or anyone to query the data with a WKT Polygon and request a particular service -- currently nlcd, population, we…

python interval tree

EDIT: added a couple points inline.

I'm obsessed with trees lately -- of the CS variety, not the plant variety. Although we are studying poplar, so I'll be using trees to study trees.
I'd tried a couple times to implement an interval tree from scratch following the Wikipedia entry.
Today I more or less did that in python. It's the simplest possible form. There's no insertion (though that's trivial to add), it just takes a list of 'things' with start and stop attributes and creates a tree with a .find() method.
The wikipedia entry that baffled me was about storing 2 copies of each node's intervals--one sorted by start and the other by stop. I didn't do that as I think in most cases it won't improve lookup time. I figure if you have 1 million elements and a tree of depth 16, then you have on average 15 intervals per node (actually fewer since there are the non-leaf nodes). So I just brute force each of those nodes and move to the next. I think th…

twill with XHTML (not viewing HTML)

Since I couldn't find this anywhere, I'll add it here for those who have the same problem:

I was trying to test a website with twill and got this at the end of my traceback:

raise BrowserStateError("not viewing HTML")
BrowserStateError: not viewing HTML

After spending a bunch of time making sure that, yes, it was spitting out HTML, I figured out that it specifically means that twill (actually mechanize) doesnt like XHTML.

You can likely fix it by adding this at the top of the script:

b = twill.get_browser()
b._browser._factory.is_html = True
twill.browser = b

Presumably, there's a real reason that check is in place, but works-4-me...

appengine memcache memoize decorator

[NOTE: see the 2nd comment below about using a tuple as a key. better to just use pickle.dumps]
I've been playing with google appengine lately. I'm working on a fun, pointless side project. Here's what I came up with for a cache decorator that pulls from memcache based on the args, kwargs and function name if no explicit key is given. The code for creating a key from those is from the recipe linked in the docstring.
a decorator to use memcache on google appengine.
optional arguments:
`key`: the key to use for the memcache store
`time`: the time to expiry sent to memcache

if no key is given, the function name, args, and kwargs are
used to create a unique key so that the same function can return
different results when called with different arguments (as

NOTE: actual usage is simpler as:
def some_function():

but doctest doesnt seem to like that.

>>> import time

>>> def slow_fn():
... time.sleep(1.1)

genedex.fasta with numpy.memmap

EDIT: added job posting to comments.
I've been working a bit on genedex, I'm still not happy with the way it stores features. Which is a huge pickle of dictionaries where every dictionary is a 'feature' that looks like: {'name':'At2g26540', 'start': 1234, 'stop': 3456, 'strand': 1, 'chr': 2}. So the only way to do a search is by location--and that is _very_ fast, thanks to rtree, but there's no way to search by name or any other attribute--and an entire organism is loaded into memory at once--that part actually works out ok, but it feels dirty. I quickly wrote an SQLAlchemy backed interface to a simple db schema do allow this sort of searching here: That already supports Feature.upstream(), downstream(), etc. methods, but it will work nicely once python supports sqlite rtree without any extra work--for now, it just uses BTree indexes on the st…

choosing django

I prefer sqlalchemy and genshi (or mako) and was therefore looking at using turbogears, but I saw a demo of the django admin, and that sold me. Certainly the templating language did not. Before this, I'd only used in my projects. These are the things I've liked/noted:

The first and most important: community. (Oddly enough, as I write this there are 666 projects tagged as django. 'turbogears', 'tg2', 'tg' give less than 50 projects combined. Think someone might have already written what you need? yep.
Also, a great site:, where I've learned a lot just by reading, and saved myself a lot of time, by extending ideas there.
And the development is active.

Second, django.contrib.* User authentication is simple, and check google-code for various alterations on the theme.
admin. This was what first made me decide on django. And now, new-forms admin is in trunk. This gives you a pretty nice CRUD interface for models in your…

pylab matplotlib imagemap

UPDATE 7-10-08:
+ add example for scatter plot
+ link to ken-ichi
Figuring how to make a client side image map from a matplotlib image has stumped me more than once. Andrew Dalke does have a working example. Below, I have the minimal example.

It's simple once you get the steps right: just use mpl's transform() to convert the data into the image's coordinate system. Then flip the y-axis as required by the imagemap, then do the normal imagemap stuff and save the html. The only real gotcha, is to make sure to put the dpi in the call to savefig().

import pylab
import sys
import random

name = 'imap'

# make some fake data
xs = range(15)
ys = [random.choice(xs) for i in range(len(xs))]

xys = zip(xs, ys)

# can also use : f = pylab.subplot(121)
f, = pylab.plot(xs, ys, 'ro')
dpi = f.figure.get_dpi()
height = f.figure.get_figheight() * dpi

# convert the x,y coords into image coords.
transform = f.get_transform()
icoords = transform.transform(xys)

# the minimal 'template' to g…

binary search over intervals

[EDIT: update location of code repo]

This isn't particularly advanced or clever, it's just a simple implementation--less code than anything else I could come up with.

Binary search is easy. Just look at the python std library implementation (and the C API version). When you play the game with a friend of guessing a number between 0 and 100, you guess 50, your friend tells you "higher", you guess 75. That's pretty much binary search. It takes about 7 guesses max to guess a number between 0 and 100. It just requires that the numbers be in order.
Interval search is more difficult. It's not just looking for a single value, but rather for a range of values that overlap a given interval. Also, you can't sort on just start, because some intervals are longer than others, so when sorting by start, the stops may be out of order. So, you have to arrange some protocol. In all the examples I've seen, including the explanation here, that means storing not only the s…


I agree with every report I've seen. Wherecamp was awesome. I've been telling people, and I'm still sure it's true, that I met exactly zero people who I'd physically seen before. Ordinarily, I avoid meetings, but this is a good format and seems to attract good people. It's fun to meet and work with people who are really into what they do. The talks are less "talky" and more like chat sessions--which is possible when the groups are small.

There was also plenty of time to hack, which was the original reason I went. During and after, I learned some simple things which I'm trying to incorporate into my usual workflow:
In the shell, background a job with "ctrl + z" then get back to it with %i where i is the number shown in the output from "jobs". That's a trick from jlivni.

From crschmidt, I added:
alias doctest="nosetests --with-doctest --doctest-extension=.txt"
to my .bash_aliases. Which let's me do:
doctest tests/

slicehost, trac, wherecamp

I have a development "server" here beside me. It's actually a budget laptop that sold for $799 2 years ago. It's a xubuntu machine, hosting a trac instance, a development server for mapping stuff, postgresql/postgis, mapserver, mysql, and couple svn repos, anything I do for contracting, etc. Oh, and it's also hosting a couple of sites for the multi-national company that my gf works for! all of their servers are windows machines (long rant suppressed).
It used to get warm, so propped it up on 4 tuna cans, 1 for each corner, now it stays cooler. Yep, it's a sweet setup.
Anyway, I pay AT&T or SBC --or whatever they are now called-- for static IP's and a supposedly faster internet connection. My 1 year contract for that is nearly up, so I'm switching to slicehost.

I'm not a sys-admin, I sorta do that for 4 gentoo (not my choice) machines at $work, and my strategy is to set up, rsnapshot and never, ever emerge -u world. ever. So far, it's mostly…

openlayers, genomes and image-maps

In response to Titus' post on using imagemaps for genomic visualization:
Why are imagemaps so popular in genomics? As an extreme and unfair comparison, just imagine if was an image map.
Given a CGI script that can accept a url like &start=1024&stop=2048&chr=3 and return an appropriate image, you can provide a substantial set of tools using openlayers, which is developed by what must be one of the largest and active developer communities in GIS. (Yes, I am an openlayers fan-boy.)
You can do that with a small addition to openlayers which I updated a couple weeks ago to OL version 2.6. In that update, I removed > 140 lines of code. So, it's now even less of a change to OL. Maybe when 2.7 comes out, I'll figure out how to provide a patch that allows an extra argument to the OpenLayers.Map constructor that limits panning to the horizontal direction -- in which case genome-browser will cease to exist and only the single file containing OpenLay…

seqfind: levenshtein + bktree

I've copied this recipe that I modified before, and added the BK Tree structure in cython. It's in my repo here.
Check it out with:svn checkout
or easy_install withsudo easy_install

It's now using the Damerau-Levenshtein distance which is more sensible for bioinformatics where transpositions are frequent.

Bearophile's original implementation used a tuple, which made sense, but in Cython, it's more efficient to use an object where the properties can be typed--as a class is converted to a c-struct--so there is no conversion when appending to a python array -- if i understand the generated c code correctly.

Using an object also allows arbitrary info to be passed along with the word when creating the tree, again, this is important for bio-informatics when the string is something like "actgcc ... acgtc" and it's useful to attach some annotation to it like:

words = [Wor…

flash (n)back

The PNAS article linked here found subjects could improve IQ with training. I've written a simple flash version of their protocol over a couple long evenings in haxe/flash.

The article methods list 2 stimuli, a moving box, and spoken letters. The test subject is to respond (click in my case) when the box position or the spoken letter is the same as it was 2 time steps ago. Where 2 is increased as the subject gets better. I didn't do sound, I just show a big letter. Clearly, the logical thing to do is use it for a couple weeks and then implement the sound when I'm smarter. (I've never really used swfmill, but I think that'd be useful here...)

The article is ambiguous about when the letter is to sound, I've made both the letter and the box appear at the same time. The default, as in the article is to have 3 seconds between events, and to show the box for 0.5 seconds. I also add some indication of whether the answer was correct (green +) or not (red -). That actua…

levenshtein in cython

EDIT(2): fix markup for <char *> casts ... fix malloc (see comments. thanks Bao).
NOTE: using a kwarg for limit slows things down. setting that to a required arg and using calloc for m2 speed things up to nearly as fast as the pylevenshtein.

Well, it seems to be popular to code up the levenshtein. I actually have a use for this and wanted to practice some Cython, so I've written a version. I used bearophile's recipe, wikibooks, this (from k4st on reddit) and this for reference. It follows bearophile's code closely, using only O(m) space instead of O(mn).

cdef extern from "stdlib.h":
ctypedef unsigned int size_t
size_t strlen(char *s)
void *malloc(size_t size)
void free(void *ptr)
int strcmp(char *a, char *b)

cdef inline size_t imin(int a, int b, int c):
if a < b:
if c < a:
return c
return a
if c < b:
return c
return b

cpdef int levenshtein(char *a, char *b, int limit=100):
cdef int m = strlen(a)…

numpy to tiff via gdal

EDIT: 7 months later I came back to this and found an error. update in the code below with old line commented out.

Rather than venting about a project I've recently decoupled myself from, I'll try to do something constructive... I also posted this to the gispython mailing list, but I've had to figure it out a couple times, so I'll put it here for the record. Given an N * N numpy array, and a bounding box, it's actually fairly simple to make a georeferenced tiff:

from osgeo import gdal, gdal_array
import numpy
from osgeo.gdalconst import GDT_Float64

xsize, ysize = 10, 10
a = numpy.random.random((xsize, ysize)).astype(numpy.float64)

xmin, xmax = -121., -119.
ymin, ymax = 41., 43.

driver = gdal.GetDriverByName('GTiff')
# bad: out = driver.Create('a.tiff', a.shape[0], a.shape[1], 1, GDT_Float64)
# the args to Create are 'name', xsize, ysize. and .shape[0] is rows, which is y.
driver.Create('a.tiff', a.shape[1], a.shape[0], 1, GDT_Float64)


python script as wsgi, cgi, or standalone

See below for original, I realized this could be done cleanly with a decorator.
The decorator wrapplication takes the number of the port to use when called as a standalone server. The EMiddle class is unnecessary, it's just used as middleware to update the environ to show it came via wsgi. If there's a cleaner way, let me know.

import os

class EMiddle(object):
def __init__(self, app): = app
def __call__(self, env, start_response):
env['hello'] = 'wsgi'
return, start_response)

def wrapplication(port):
def wrapper(wsgi_app):
if 'TERM' in os.environ:
print "serving on port: %i" % port
os.environ['hello'] = 'standalone'
from wsgiref.simple_server import make_server
make_server('', port, wsgi_app).serve_forever()

elif 'CGI' in os.environ.get('GATEWAY_INTERFACE',''):

Genedex: query genomic features and sequence

Normally, I don't write libraries, I figure smarter people than I should do such things, and I should just use them. But, I got tired enough of writing one-off scripts for genomic feature manipulation-- find the upstream, downstream neighbors and get the sequence -- and I saw enough of the pieces coming together that I decided to build it. I'd complained before about how rtree didn't support 1D indicies. Not only is this not a problem, it's beneficial. Genomic features should have strand information, so that's the 2nd dimension. Then rtree does containment queries, so it's simple to find only the features on a given strand. I realized this about the same time that the docstring for numpy's memmap went from 0 lines to about 100, and it was enhanced to take a filehandle, not just a filename. This means you can send in a start position and a shape to the numpy.memmap constuctor and it can create a numpy array of only that chunk. This means that it's possib…

comparative genomics with openlayers

Traditional genome browsers, look like this. In fact, I think that's the most popular genome-browser used--gbrowse. They display information in tracks, so any layer of annotation you just add on to the bottom of the image (after making the image taller). This doesnt work for genome-browser, the hack of openlayers to support only horizontal scrolling, because you if you have 2 adjacent tiles, if one has more features than the next, there's not guarantee that they'll be the same height, and no guarantee that a feature that's on both images will align correctly.

I was just hacking around, trying to test some work I'd done and realized that you can have annotation layers with OpenLayers, just add another map, and tie them together!

So that's 2 OpenLayers.Map() instances. What makes this easy is the new Map.panTo() methods in OpenLayers 2.6 (which is in release candidate 1). So, the top map registers for 'move' and 'zoomend' events with callbacks that…

featureserver authentication

As the name implies, featureserver serves vector features to various formats from a number of datasources, including OGR -- which means pretty much any vector format. That's extremely powerful. Really. That means, for instance, that when you're working on a really cool project and all anyone wants to know is if they can see it in KML/Google Earth, it's no extra work. Just point them to the REST-ful url like "", and continue working on the cool project. Likewise for all.gml, .atom, etc. And, if you have a project with spatial data, if you put it in a format that featureserver understands, it's displayable, and editable in openlayers.

The next thing people want in a web application is some sort of user restrictions. In featureserver, by default, anyone can do any of the CRUD operations on any feature. I've been playing with a soon-to-be-open-sourced PPGIS (apparently the trendy acronym for that is now VGI) project wher…

reading code

A fasta file of rice genomic sequence is 355MB. It's not easy to understand how large that is. This is an attempt to come up with a quick metric.
So, I downloadedUlysses.
wc shows it to have 267235 words. Some googling says the average person can read 250 words per - minute. So that's 267,235 / 250 / 60 = 17.8 hours. Well, it's hard to believe anyone can really read Ulysses in 18 hours but... good enough.
So on the rice fasta file i ran:grep -v ">" rice.fasta | wc -cto get rid of the 12 header lines (1 per chromosome) and only count sequence (should be within 12 characters counting the extra new-lines). That gives 372,077,765 characters. The average word-size in ulysses is 5. I rounded up to 6. So, the rice sequence has the equivalent of 372,077,765 / 6 = 62,012,960 words
So, at 250 words per minute, it'd take:
62012960 / 250 / 60 = 4,134 hours to read the rice genome. That's 172 days. Also, from what I know, the plot is hard to follow.
Genome size varies wi…

point partitioning

After you spend all day banging your head against your own problems, sometimes it's just nice to bang it on something else for a bit.
This question came through on the postgis mailing list and it seemed like a good diversion. I think it's a very clear description of the problem. To quote:
I have around 300,000 points, each with a lat, lon and altitude (also converted to geometry). I need to get a subset of those points, where none of them are within 5m (or some other arbitrary distance) of each other. It doesnt matter which points get picked over another, as long as whatever the data set it creates, that none of the points are within that 5m radius and that relatively most of the points are used

So, I hacked up a quick solution. It's probably inefficient -- deleting keys from a dict, and removing entries from an rtree index. But, it's easy to understand, and (without the plotting) it runs in about 2 minutes for the requested 300000 points.
When plotting, the image looks …

OGR python projection

OGR Projection

If you're using shapely and you need to do projections, you'll either have a lot of boilerplate or a function like this one. Actually, even in OGR, there's a lot of bioler plate involved in transforming....

from osgeo import ogr
from shapely.wkb import loads

def project(geom, to_epsg=900913, from_epsg=4326):
"""utility function to do quick projection with ogr,
to and from shapely objects
>>> from shapely.geometry import LineString
>>> l = LineString([[-121, 43], [-122, 42]])
>>> lp = project(l, from_epsg=4326, to_epsg=26910)
>>> lp.wkt
'LINESTRING (663019.0700828594854102 4762755.6415722491219640, 582818.0692490270594135 4650259.8474613213911653)'

to_srs = ogr.osr.SpatialReference()

from_srs = ogr.osr.SpatialReference()

ogr_geom = ogr.CreateGeometryFromWkb(geom.wkb)

spatially explicit metapopulation models in scipy.

Making Pretty Pictures
I started to learn to program about 5 years ago running population ecology models in mathematica. Yesterday, I found an old mma notebook with a model modified to include differential parasitoid dispersal to adjacent host cells depending on the host density in those cells. It's bascially a discrete-time Nicholson-Bailey model. But in a grid of cells, where each cell contains a population of hosts (H) and parasitoids (P) that give birth, die, eat, and get eaten according to the NB model. Each generation, following birth/reproduction/predation, the hosts and parasitoids disperse. The hosts disperse equally to the 8 surrounding cells in their neigbhorhood. The parasitoids can move irrespective of host densities when the aggregation parameter (eta) is 0. When aggregation is 1 (eta == 1), the parasitoids move to adjacent cells in exact proportion to host densities in each of the surrounding cells. muH and muP (i'm too lazy to figure out how to write the symbols…

rtree: know your nearest neigbhors

My computer spends a lot of time looking for neighbors of a given location-- even more so for bio, than for geo. This is what I've learned about the options for doing smarter search so far.

SELECT * from (
(SELECT * FROM ((SELECT * FROM feature WHERE start<= ? ORDER BY start DESC LIMIT 1) UNION (SELECT * FROM feature where start>= ?
ORDER BY start LIMIT 1)) as u)
(SELECT * FROM ((SELECT * FROM feature where stop<= ? ORDER BY stop DESC LIMIT 1) UNION (SELECT * FROM feature where stop>= ?
ORDER BY stop LIMIT 1)) as v)
) as w
ORDER BY ABS((start + stop)/2 - ?) LIMIT 1

if you fill in ? with an integer location, that query will return the closest feature most of the time. It's verbose if not ugly, and that's only for 1 dimension. It can return the wrong feature in certain cases.... You have to write it like that in MySQL, because it doesnt support functional indexes, so as soon as you do something like:
ORDER BY ABS((start + stop)/2 - ?)
it's no longer an inde…

What a Shapely genome you have!

This might be a case of if you have a really cool hammer, everything looks like a nail, but it was fun mixing tools from different disciplines.

After finding synteny, there's a bunch of paired genes whose neighbors are also pairs. Paired (homologous) genes have similar sequence because they have some function and can't change without loss of function. Non-gene sequence between the paired genes is mostly randomized via mutation, deletion, etc. But, there is non-gene sequence that is conserved between the genes. These CNS's-- conserved non-coding sequences--are usually sites that bind stuff that regulates the expression of a gene.
That looks like this.

With one gene on the top, and its pair below, both yellow. Pink lines in the foreground connect putative CNSs (similar sequences) between these genes. That the lines cross is bad. CNSs occur right at the level of noise. So even though a similar sequence occurs near both genes, it could be by chance. It is possible to reduce thi…

flash, vi, fcsh

All my flash tinkering has been in VIM-- no IDE, no XML, just actionscript. It's a little tough to deal with the adobe compiler as it takes about 11 seconds to compile a large project like modestmaps on my machine. That's not good for a guess-and-check programmer. The typing does catch some errors.

The worldkit project compiles instantaneously with mtasc (the predecessor to haxe)--likewise for the as2 branch of modestmaps. The flash compiler shell drops the compile time for as3 modestmaps to under 3 seconds, so I've added this to my .bash_aliases:

alias fcsh="/usr/bin/rlwrap /opt/src/flex2/bin/fcsh"

the rlwrap is to use readline in the flash shell--meaning I can just press up-arrow to get the previous compile command. By default, one has to paste or type the entire command again.
With that, it's close to a reasonable workflow.

synteny mapping

Living in Synteny
I've been working on automating synteny mapping between any pairs of genomes. Synteny is where there's a stretch of DNA or genes in some order on chromosomeA of organismX and due to a shared evolutionary history, you can find a similar stretch of genes in order on chromosomeB of organismY. Often there are small losses and inversions, but between closely related organisms like man and mouse, there's still a lot of synteny.
Plants can undergo polyploidy, following which, a species can have 2 entire copies of its genome. Over time, much of the duplicated cruft is lost, and the homologous chromosomes diverge, but if the divergence is not too great, it's still possible (actually common) to find synteny within the genome of a single organism--as well as between organisms.
I've written my own algorithm to find synteny which uses python sets, and numpy array slicing to do the heavy lifting. It is quite clever [wink]. And it _almost_ works but it's ...…

open source gis and flash maps part two

Mash Flap
I started looking into flash mapping stuff lately. For the patch I submitted to worldkit, Mikel gave me commit access! So, now the svn version of worldkit can be compiled with mtasc by typing "make". I feel unreasonably proud of that, given that much of what I did was some global search and replace stuff in VI, and then read and fixed mtasc compiler errors until they went away. It was good fun.
Michal Migurski saw in that same post that I mentioned modestmaps and gave me some good ideas on getting WMS going. I just figured out how to get that working and posted a message to their overly web2.0 forums. Hopefully someone with some real actionscript skillz will clean it up. A mapping library without a good WMS interface is much less useful for most of the stuff I do.

I haven't decided whether to use modestmaps or worldkit, or both. The time stuff the Mikel has done in worldkit is very cool and I haven't really looked at that yet. But I have a time based pr…