from the desk of stinkpot

strip all non-alphanumerics or all non-letters from a string in python

Lawrence David — Tue, 16 Mar 2010 15:38:29 +0000

to strip all the non-letters from a python string named ‘my_str’, you can use the following one-liner:

”.join([c for c in my_str if c.isalpha()])

to strip all the non-alphanumeric characters from that python string, use the slightly modified:

”.join([c for c in my_str if c.isalnum()])

use fast fourier transform (fft) to perform low-pass filtering

Lawrence David — Sun, 13 Dec 2009 22:27:23 +0000

here’s an easy way to do low-pass signal filtering in matlab:

function [s_data_v] = fftsmooth(data_v,freq_n)
% use fft low pass filter to smoothen out a signal

fft_data_v = fft(data_v);
s_fft_data_v = zeros(1,length(data_v));
s_fft_data_v(1:freq_n) = fft_data_v(1:freq_n);
s_fft_data_v(end-freq_n:end) = fft_data_v(end-freq_n:end);
s_data_v = real(ifft(s_fft_data_v));

move x-axis to top of matlab figure

Lawrence David — Sat, 05 Dec 2009 23:35:54 +0000

to move the x-axis on a figure from the bottom of your plot to the top, adjust the ‘xaxislocation’ variable of your current axis handle:

matlab>> set(gca,’XAxisLocation’,'top’)

install macports emacs in snow leopard

Lawrence David — Tue, 24 Nov 2009 18:14:32 +0000

when trying to install emacs using macports on my new snow leopard install, i got the following error:

foo://opt/local/sudo port install emacs
—> Computing dependencies for emacs
—> Fetching emacs
—> Verifying checksum(s) for emacs
—> Extracting emacs
—> Applying patches to emacs
—> Configuring emacs
—> Building emacs
Error: Target org.macports.build returned: shell command ” cd “/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_editors_emacs/work/emacs-22.3″ && /usr/bin/make -j2 all ” returned error 2
Command output:                            __la_symbol_ptr 0×100152070    0×628
__program_vars   0×1001526a0     0×28
__const          0×1001526e0    0×730
__data           0×100152e20 0×1df3e8
__bss            0×100332220 0×51830
__common         0×100383a60 0×103f9
3 LC_SEGMENT_64          72 __LINKEDIT       0×100394000 0×46000
4 unknown                48
5 LC_SYMTAB              24
6 LC_DYSYMTAB            80
7 LC_LOAD_DYLINKER       32
8 LC_UUID                24
9 LC_UNIXTHREAD         184
10 LC_LOAD_DYLIB          64
11 LC_LOAD_DYLIB          56
0×100dfc080 (sz:   0×3f24/ 0×3f28)
0×100d00000 (sz: 0×4a6d5/ 0xfc080)
0×100afc080 (sz:   0×3f25/ 0×3f28)
0×100a00000 (sz: 0xfc07f/ 0xfc080)
0×1017f8000 (sz:   0×26ca/ 0×7fa0)
0×101000000 (sz: 0×26a7fd/0×7f8000)
0×10044c000 (sz:        0/ 0×1000)
— Load Commands written to Output File —
Writing segment __PAGEZERO       @        0 (       0/0×100000000 @          0)
Writing segment __TEXT           @        0 (0×152000/0×152000 @ 0×100000000)
Writing segment __DATA           @ 0×152000 (0×242000/0×242000 @ 0×100152000)
section __nl_symbol_ptr at 0×152000 - 0×152070 (sz:     0×70)
section __la_symbol_ptr at 0×152070 - 0×152698 (sz:    0×628)
make[1]: *** [emacs] Error 1
make: *** [src] Error 2

Error: Status 1 encountered during processing.

to resolve:

download the patch file found here.
install the patch: foo://opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_ports_editors_emacs/work/emacs-22.3/sudo patch -p0 < ~/Downloads/emacs-snow-leopard.patch
sudo port install emacs

get aac playback working in squeezeboxcenter in debian

Lawrence David — Wed, 11 Nov 2009 02:44:46 +0000

upgraded from squeezebox center 7.1 to 7.4 today and my aac playback broke.

to fix, i had to add the following lines to my convert.conf file:

mov mp3 * *
# FB:{BITRATE=-B %B}
[faad] -w -f 2 $FILE$ | [lame] –resample 44100 –silent -q $QUALITY$ $BITRATE$ -x -r - -

mov wav * *
# F
[faad] -w -f 2 $FILE$

mp4 mp3 * *
# FB:{BITRATE=-B %B}
[faad] -w -f 2 $FILE$ | [lame] –resample 44100 –silent -q $QUALITY$ $BITRATE$ -x -r - -

aac mp3 * *
# FB:{BITRATE=-B %B}
[faad] -w -f 2 $FILE$ | [lame] –resample 44100 –silent -q $QUALITY$ $BITRATE$ -x -r - -

aac playback still wasn’t working, so i went to:

settings -> advanced ->logging

and enabled “debug” logging for player.source.

parsing the logfile output revealed the following line:

[09-11-10 21:20:08.1582] Slim::Player::Song::open (548) Tokenized command “/usr/share/squeezeboxserver/Bin/i386-linux/faad” -w -f 2 “/home/lad/Music/iTunes/iTunes Music/A Fine Frenzy/One Cell In The Sea/04 You Picked Me 1.m4a” | “/usr/local/bin/lame” –resample 44100 –silent -q 9 -B 320 -x -r - - & |

strangely, trying to execute:

> /usr/share/squeezeboxserver/Bin/i386-linux/faad

led to an error where linux claimed the file faad didn’t exist. removing the faad file from /usr/share/squeezeboxserver/Bin/i386-linux/ caused squeezebox center to search for faad in the default linux location (/usr/bin).

i reloaded and suddenly, angels sang.

how to restore from a time machine smartbundle

Lawrence David — Sat, 07 Nov 2009 22:15:47 +0000

let’s say you’ve gone and done something rash and created a DIY time capsule. how do you restore from the backup if your hard drive goes belly up?

get a working hard drive and install a fresh copy of os x
create a new user (try and give that user a username different from your old user name)
log on as the new user. connect to the server hosting your smartbundle backup.
drag the smart bundle to disk utility’s left pane. double click to mount.
open “migration assistant” and select restore from a “time machine backup.”
cross your fingers and hope for the best!

remove matlab tickmarks (but keep labels)

Lawrence David — Mon, 14 Sep 2009 17:28:54 +0000

to set the length of tickmarks to 0, try this command:

>> set(gca,’Ticklength’,[0 0])

using python to do perl-like text manipulation

Lawrence David — Tue, 07 Apr 2009 15:04:51 +0000

to do string substitutions in python, use the “re” module and the “sub” function:

>>> import re

…

>>> test = “2545423/1-4242:0.3245″

>>> test ; re.sub(”/\d-\d*:”,”:”,test)
‘2545423/1-4242:0.3245′
‘2545423:0.3245′

and, to match a group and then use it in the substitution, use parentheses and the \ operation:

>>> new_boot_s = re.sub(”(\d+:)”,”n\\1″,boot_s)

handle ps2pdf dependency errors with ghostscript

Lawrence David — Tue, 07 Apr 2009 03:49:03 +0000

while trying to upgrade my packages, i got caught with the following error:

Removing ghostscript …
Purging font configuration of gs…
No alternatives for ps2pdf.
dpkg: error processing ghostscript (–remove):
subprocess pre-removal script returned error exit status 1
Errors were encountered while processing:
ghostscript
E: Sub-process /usr/bin/dpkg returned an error code (1)

to solve it, i edited the following file:

/var/lib/dpkg/info$ sudo emacs ghostscript.prerm

by commenting out the lines referring to ps2pdf. after that, sudo apt-get install -f worked!

wait for an executed subprocess to complete in python

Lawrence David — Mon, 09 Mar 2009 15:32:16 +0000

if you call a shell process from python, your script will normally trundle along without pausing for that process to complete. if you’d like the process to finish before your script continues on, use the communicate method:

proc = sub.Popen(my_job,stdout=sub.PIPE)
stdout,stderr = proc.communicate()