Pass data on the fly to factory_boy factory using custom RelatedFactoryList class

factory.py

import copy

from factory import RelatedFactoryList


class RelatedFactoryVariableList(RelatedFactoryList):
    """This factory allows you to specify how many related objects do you
    want to create, but also allows you to define the data for each related
    object. 
    
    Usage example:
    
    # This will create 4 objects
    FooFactory(bars__size=4)
     
    # This will create 3 objects, with different data for each one
    FooFactory(bars__data=[{"name": "a"}, {"name": "b"}, {"name": "c"}])
    
    # Based on answer here: https://github.com/FactoryBoy/factory_boy/issues/767
    
    """

    def call(self, instance, step, context):
        size = context.extra.pop("size", None)
        data = context.extra.pop("data", [])
        if size and data:
            if size != len(data):
                raise TypeError(
                    "RelatedFactoryVariableList you can only use data or size, not both."
                )

        if not size and not data:
            size = self.size

        if size and not data:
            # Generate size number of objects
            return [
                super(RelatedFactoryList, self).call(instance, step, context)
                for i in range(size)
            ]
        results = []
        for d in data:
            # Create copy of PostGenerationContext object
            copied_context = copy.deepcopy(context)
            if isinstance(d, dict):
                # Update data for each factory instance
                copied_context.extra.update(d)
            results.append(
                super(RelatedFactoryList, self).call(
                    instance, step, copied_context
                )
            )
        return results