They actually are quite different.
In VENUS, as you know, a liquid class specifies many parameters, like aspiration flow rate, volume correction, etc. The user has to specify the liquid class using a string.
In PyLabRobot, a liquid class is basically an enumeration of the different types of liquid that one would use (water, DNA, glycerol, etc.) See https://github.com/PyLabRobot/pylabrobot/blob/main/pylabrobot/liquid_handling/liquid_classes/abstract.py. The default is water. Each robot (LiquidHandlerBackend) can use this information about the type of liquid to determine the best aspiration/dispense parameters. Note that this is intended to fill in parameters with value Default, and that user specified parameters should always take precedence. This ‘filling in of defaults’ is done on a parameter-by-parameter basis, so if you specify a flow rate for example, the best volume correction curve will still be found automatically. If no flow rate were specified, that parameter would also have a ‘smart default’.
In the STAR backend specifically, which is the one used for Hamilton robots, the available information is combined to find the best VENUS liquid class. That is done by combining the PLR Liquid Class (say “water”), with other information (such as whether an operation is an aspiration or dispense, whether it’s a jet or surface dispense, etc.). Using this combination, the best VENUS Liquid Class is found (see https://github.com/PyLabRobot/pylabrobot/blob/main/pylabrobot/liquid_handling/liquid_classes/hamilton.py#L122). Currently, no option exists to manually specify a liquid class in STAR, but I could add that if you want.
The venus liquid classes that exist in PyLabRobot can be edited by editing the Python file, but I would not necessarily recommend this. It would be much better if we could just have the user pass a liquid class using a parameter, in case they want to override the automatic selection. Let me know if you need that.
This is not the default behavior, or necessarily recommended, since it complicates robot agnosticism, and ‘plain’ parameters are much simpler and more expressive. So I would recommend setting the parameters in LiquidHandler:
- https://docs.pylabrobot.org/_autosummary/pylabrobot.liquid_handling.liquid_handler.LiquidHandler.aspirate.html
- https://docs.pylabrobot.org/_autosummary/pylabrobot.liquid_handling.liquid_handler.LiquidHandler.dispense.html
Or, if need be, using backend_kwargs (parameters that are ignored by LiquidHandler and passed along to the backend, so basically the parameters you see here):
- https://docs.pylabrobot.org/_autosummary/pylabrobot.liquid_handling.backends.hamilton.STAR.STAR.aspirate.html
- https://docs.pylabrobot.org/_autosummary/pylabrobot.liquid_handling.backends.hamilton.STAR.STAR.dispense.html
If anything here sounds imperfect, I’m happy to discuss alternatives!
Hope that helps!