part-1.md

Session 3.1: Templating and launching shell commands (13:00 - 14:00)

Exercise: Based on a program input template create a series of files (45 min)

Consider the following example POV-Ray input file:

// source: http://www.csb.yale.edu/userguides/graphics/povray/demo.pov.html

#include "colors.inc"

background { color Cyan }

camera {
  location <0.0, 2.0, -3.0>
  look_at <0.0, 1.0, 2.0>
}

sphere {
  <0.0, 1.0, 2.0>, 2.0
  texture {
    pigment { color Yellow }
  }
}

light_source { <2.0, 4.0, -3.0> color White}

Imagine you wish to create many (tens or hundreds) input files where you vary either the sphere radius or the sphere origin or both. Create a script to create many input files.

Together:

• Discuss strategies on how to tackle this problem.

In pairs:

• Try to solve this problem.
• It is also totally fine if you prefer to work on a similar example which is closer to your domain or workflow.

Together:

• Discuss possible solutions.

Running a shell command out of Python (15 min)

Write a Python script which executes a shell command.

First, using os.system(), e.g.:

import os
os.system('echo hello from your shell')

Then, using subprocess.check_output() e.g.:

import subprocess
output = subprocess.check_output(['echo', 'hello', 'from', 'your', 'shell'])

• Discuss when it could be useful to execute a shell command or a binary from Python.
• Discuss the advantages/disadvantages of the two approaches.