title: Conditional execution of code segments
body: <p>I am working on a data set using both my laptop and a cloud facility. I want to compute some "computation-heavy" code chunks only when working on the cloud.</p>
  
  <p>So far, I have chosen a not very elegant way to do so. I have added <code>##OPT##</code> prefixes to segments which I want to execute only when in the cloud. I then simply remove these prefixes and run the script when in the cloud.</p>
  
  <p>Now my question: is there a way that I can select in the beginning of the script once whether to execute these segments or not and then skip these segments if the argument is set to "false"? I have tried with if conditions but this is very cumbersome.</p>