Function: register_function

qgis.core.register_function(function, args='auto', group='custom', usesgeometry=False, referenced_columns=['#!allattributes!#'], handlesnull=False, params_as_list=None, **kwargs)

Register a Python function to be used as a expression function.

The function signature may contain special parameters (in any order at the end of the signature):

If those parameters are present in the function signature, they will be automatically passed to the function, without the need to specify them in the expression.

Functions should return a value compatible with QVariant Eval errors can be raised using parent.setEvalErrorString(“Error message”)

Parameters:

  • function – the Python function to be used as an expression function

  • args – DEPRECATED since QGIS 3.32. Use params_as_list if you want to pass parameters as a list.

  • group – the expression group in which the function should be added

  • usesgeometry – Defines if this expression requires the geometry. By default False.

  • referenced_columns – An array of names of fields on which this expression works. By default [QgsFeatureRequest.ALL_ATTRIBUTES]. Specifying a subset of fields or an empty list will result in a faster execution.

  • handlesnull – Defines if this expression has custom handling for NULL values. If False, the result will always be NULL as soon as any parameter is NULL. False by default.

  • params_as_list – If True, the function will receive the expression parameters as a list. If False, the function will receive the parameters as individual arguments. False by default.

Keyword Arguments:

  • register (bool): Set to False to create the QgsPyExpressionFunction without registering it. Useful for testing puposes. By default True.

  • name (str): If provided, replace the function name

  • helpText (str): If provided, used in the help tooltip instead of the function docstring

Returns: