Class: register_function

class 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): - feature: the QgsFeature related to the current evaluation - parent: the QgsExpressionFunction parent - context: the QgsExpressionContext related to the current evaluation

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”)

  • 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 field names on which this expression works. By default [QgsFeatureRequest.ALL_ATTRIBUTES]. Can be set to None for slightly faster evaluation.

  • 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