Sier2 Blocks

This library provides useful blocks for sier2.

A block is implemented as:

class MyBlock(Block):
    ...

The Block class inherits from param.Parameterized, and uses parameters as described at https://param.holoviz.org/user_guide/Parameters.html. There are three kinds of parameters:

• Input parameters start with in_. These parameters are set before a block is executed.
• Output parameters start with out_. The block sets these in its execute() method.
• Block parameters start with block_. These are reserved for use by blocks.

A typical block will have at least one input parameter, and an execute() method that is called when an input parameter value changes.

class MyBlock(Block):
    in_value = param.String(label='Input Value')
    out_upper = param.String(label='Output value)

    def execute(self):
        self.out_value = self.in_value.upper()
        print(f'New value is {self.out_value}')

The block parameter block_pause_execution allows a block to act as an "input" block, particularly when the block hsa a GUI interface. When set to True and dag execution reaches this block, the block's prepare() method is called, then the dag stops executing. This allows the user to interact with a user interface.

The dag is then restarted using dag.execute_after_input(input_block) (typically by a "Continue" button in the GUI.) When the dag is continued at this block, the block's execute() method is called, and dag execution continues.

Many blocks are optimised for use with Panel, and have a specified __panel__ method. This should return a panel-interpretable object which is displayed within a card when used in a PanelDag. If __panel__ is not defined, the in_ params will be used to automatically generate one.