Things I learnt implementing a custom procedure

nsriram

This information can be useful for those will use inline scripts for more flexibility. Some things to be aware of:

1. Difference between "prepare" and "run" tabs. These can also be called in python script as functions prepare() and run(). Needless to say "run" happens only when the object is run but prepare usually happens before that. If there is a trialsequence that is defined, one can call it by exp.items["trialsequence"].prepare() and exp.items["trialsequence"].run() In inline scripts sometimes you will get an error message saying that so and so variable is not defined before use. Chances are that you need to move those definitions in the prepare phase and all will be well (especially for global vars). So maybe if you have a fixed set of global vars, one can make a single global vars inline script with all the definitions and initializations in the prepare phase. Subsequent scripts can all execute solely from the run tab and conceptually that is easier to think about.

2. Understanding exp.get("varname") and exp.set("varname",value). These are handy because they can create or modify variable values outside the current scope. However it appears that if the set is done within a for loop, for example, then the scope may not be as global as one might think it is. Takes getting used to how scope works in OpenSesame.

3. A bigger hammer that can be used is the global varname to ensure that varname is available in all scopes for read as well as modify. But in case you are modifying, take care to declare global varname in the inline script before modification. It seems that exp.set can be used to modify global variables but even direct python code also seems to works such as globalvariable += 1 increment operator.

4. When using scripting, for some of the keyobjects they can be turned off in the main sequence. That is replace run if always with run if never. Reason being that we wish to control their execution using scripts.

5. While using inline scripting, I did not use the loop object and did not use the facilities in the logger (except to modify the script view to log exactly the things of interest).

6. I preferred to use the print x to debug rather than look at the variable inspector (too much clutter) and just see the debug window printing various values.

That's all I can think of. I got tripped by scoping and the distinction between prepare and run (this is a key concept) and the usefulness of global variables.