pythonapacheweb-servicesobspy

Obspy.read() not working when called from mod_python apache module

I'm trying to make a simple web service which reads an MSEED file and outputs some information on that.

The most reasonable choice seemed to be using python with the excellent obspy module (A Python Toolbox for seismology/seismological observatories), which is widely used in the seismological community.

I succed in reading a file and getting some information from it with this simple python code:

import obspy
import numpy
import sys


my_filename = "SOME FILE"
my_start_time =  "2012-01-01T08:00:00"
my_end_time =  "2012-01-01T09:00:00"

dt = obspy.UTCDateTime(my_start_time)
et = obspy.UTCDateTime(my_end_time)
st = obspy.read(my_filename, starttime=dt, endtime=et)
....then do something....

Now, if I want to implement it as a web service, among the several different choiche I can install the mod_python on Apache, and invoke such script in a bit different way.

I do as follows (the script is in a file called test.py):

from mod_python import util
import obspy
import numpy
import sys

def index(req):
    [...]
    startdate="2012-01-01T08:00:01"
    enddate="2012-01-01T08:10:00"
    myfilename=" SOME FILE"
    dt = obspy.UTCDateTime(startdate)
    et = obspy.UTCDateTime(enddate)

    ##### read file
    st = obspy.read(my_filename, starttime=dt, endtime=et) ******
    [...]

What happens is that on the last line it hangs without giving any error. when invoking the script from my server http://localhost.my/cgi-bin/test.py it works well until the last line, then after that it doesn't even print anything but, again WITHOUT OUTPUT ERRORS

Eveno more weird, if I change the last line with

st = obspy.read(my_filename, headonly=True)

then it works.

What I tried:

  1. Changing permission to files/folders. The script and the file are in my /var/www/cgi-bin directory. Assigning readable to everyone to files and directory did not work
  2. moving files to different folders
  3. changing the owner of the file/dir (to www-data)

But it still doesn't work.

I don't understand if it is a problem of the obspy module or some limitation to the apache mod_python.

Any idea about how to solve this issue?

Solution

  • The best answer I received from obspy github issue page was the following

    It seems to be related to a memory allocation issue. You could try to update to the latest ObsPy repository version as we recently made some changes to that and see if that resolves your issue. I am pretty sure that it is not a permissions related issue.

    Otherwise, if you are not tied to using mod_python, you could try out one of the very many and oftentimes very good Python web frameworks. If you just need it for a simple webservice, a microframework might suit you well:

    http://flask.pocoo.org/ http://www.pylonsproject.org/ http://www.cherrypy.org/ Of course Django might also appeal to you.

    Cheers!