How to add BOID brain settings to a particle system via python script?

Question

I am trying to use a script to add some rules to the boid brain of a particle system and the operators on website here, https://docs.blender.org/api/current/bpy.ops.boid.html, don't seem to be doing anything. Does anyone know a way to do add various rules to a boid brain system via script?

I am using the following code to add the particle system to an existing selected object in the scene. Everything works up until the last line where I try to add the Boid rule. That line doesn't seem to do anything to the particle system.

#adding particle system with custom particle system settings for smoke explosion below
   
    obj = bpy.context.active_object

    if len(obj.particle_systems) == 0:
        obj.modifiers.new("part", type='PARTICLE_SYSTEM')
        part = obj.particle_systems[0]

        settings = part.settings
        settings.name = 'Bug System'
        settings.count = 1000
        settings.frame_start = 1
        settings.frame_end = (250)
        settings.lifetime = 500
        settings.lifetime_random = 0
        settings.emit_from = 'FACE'
        settings.physics_type = 'BOIDS'
        bpy.context.object.show_instancer_for_render = False
        settings.show_unborn = True
        settings.use_dead = True
        settings.render_type = 'COLLECTION'
        settings.particle_size = 0.05
        settings.size_random = 0.3
        bpy.data.particles["Bug System"].instance_collection = bpy.data.collections[context.scene.spyderfy_tool.my_stringbugsystem]
        settings.show_unborn = False
        settings.use_dead = False
        settings.jitter_factor = 0
        settings.object_factor = 1
        settings.effector_weights.turbulence = 0
        #adding boid brain rules in correct order
        bpy.ops.boid.rule_add(type='FLOCK')
    
    
    return{'FINISHED'}

UPDATE EDIT and Follow Up Question: lemons answer worked for adding the boid rules. The last issue I am having now is adding a goal target via the script as well? Do I need to override something here as well. I've attached the code below. Only the last line is not working. For clarification the "Bug System Goal" object is an Empty that has already been added to the scene.

#adding BOID BRAIN RULES in correct order(help from stackexchange users lemon and batfinger)
        # Copy the current context
        context_override = bpy.context.copy()
        # Override the wanted property
        context_override["particle_settings"] = settings
        # Call the operators
        bpy.ops.boid.rule_add(context_override, type='FLOCK')
        bpy.ops.boid.rule_add(context_override, type='GOAL')
        #conditional to follow bug system goal if checkbox is selected by user
        if (context.scene.spyderfy_tool.my_goalobject == True):
            bpy.data.particles["Bug System"].rules["Goal"].object = bpy.data.objects["Bug System Goal"]

SECOND UPDATE and troubleshooting: Hi Lemon thanks for the response. Using the code you mentioned to add a goal object in my script I get the following error saying that the particle system object has no attribute "settings".

Tried to fill in the gaps in my code that would be specific to my script. I must be overlooking something? The goal assignment code where the error occurs is written last under the conditional statement.

 #Now we adjust our newly appended particle system with custom particle system settings for the boids system below(from article on stackexchange)
   
    obj = bpy.context.active_object

    if len(obj.particle_systems) == 0:
        obj.modifiers.new("part", type='PARTICLE_SYSTEM')
        part = obj.particle_systems[0]

        settings = part.settings
        settings.name = 'Bug System'
        settings.count = 1000
        settings.frame_start = 1
        settings.frame_end = (250)
        settings.lifetime = 500
        settings.lifetime_random = 0
        settings.emit_from = 'FACE'
        settings.physics_type = 'BOIDS'
        bpy.context.object.show_instancer_for_render = False
        settings.show_unborn = True
        settings.use_dead = True
        settings.render_type = 'COLLECTION'
        settings.particle_size = 0.05
        settings.size_random = 0.3
        bpy.data.particles["Bug System"].instance_collection = bpy.data.collections[context.scene.spyderfy_tool.my_stringbugsystem]
        settings.show_unborn = False
        settings.use_dead = False
        settings.jitter_factor = 0
        settings.object_factor = 1
        settings.effector_weights.turbulence = 0
        #adding BOID BRAIN RULES in correct order(help from stack exchange users lemon and batfinger)
        # Copy the current context
        context_override = bpy.context.copy()
        # Override the wanted property
        context_override["particle_settings"] = settings
        # Call the operators
        bpy.ops.boid.rule_del(context_override)
        bpy.ops.boid.rule_del(context_override)
        bpy.ops.boid.rule_add(context_override, type='GOAL')
        bpy.ops.boid.rule_add(context_override, type='SEPARATE')
        bpy.ops.boid.rule_add(context_override, type='FLOCK')
        
        if (context.scene.spyderfy_tool.my_goalobject == True):
            # Get the particle object
            obj = bpy.context.object
            # Get the goal
            empty = bpy.data.objects["Bug System Goal"]

            particle_system = bpy.data.particles["Bug System"]
            # You can also:
            #particle_system = obj.particle_systems["Bug System"]

            # Get the boid part
            boids_part = particle_system.settings.boids #WHERE THE ERROR OCCURS

            # Get the state (it seems there is one boid state)
            state = boids_part.states[0]

            # Get the 'Goal' rule from its index
            # You should know its index as you've set it up earlier
            rule = state.rules[1] # '1' is an example, so
            # Or:
            #rule = state.rules['Goal'] # But may be the same name several times

            # Assign the empty as goal
            rule.object = empty

Not sure where I am going wrong here.

Answer 1

You need to override the context. Context properties are described here. And more specifically, for particle settings, here.

To make it work, just add the following to your code:

# Copy the current context
context_override = bpy.context.copy()
# Override the wanted property
context_override["particle_settings"] = settings
# Call the operator
bpy.ops.boid.rule_add(context_override, type='FLOCK')

To assign an object as goal, you can:

import bpy

# Get the particle object
obj = bpy.context.object
# Get the goal
empty = bpy.data.objects["Empty"]

settings = bpy.data.particles["ParticleSettings"]
# You can also:
# settings = obj.particles_systems["ParticleSettings"].settings

# Get the boid part
boids_part = settings.boids

# Get the state (it seems there is one boid state)
state = boids_part.states[0]
# Or:
#state = boids_part.states['State']

# Get the 'Goal' rule from its index
# You should know its index as you've set it up earlier
rule = state.rules[2] # '2' is an example, so
# Or:
#rule = state.rules['Goal'] # But may be the same name several times

# Assign the empty as goal
rule.object = empty

Answer 2

Some further notes on this.

AFAIC @lemon has provided the answer re which member is required to override. This is a little TL;DR ...looked at this prior to answer having tried "particle_system"., didn't work, put in the look at later.

The properties panel has what is known as 'BUTTONS' context which contains particle_system, particle_system_editable and particle_settings See https://docs.blender.org/api/current/bpy.context.html#bpy.context.particle_system

This is where the particle settings are displayed. If we view source in the particle tab, opening UI file bl_ui/poperties_particle.py can see that a little helper function is included to get the particle settings from context. Notice it uses either the context member available or those pinned to the panel.

def particle_get_settings(context):
    if context.particle_system:
        return context.particle_system.settings
    elif isinstance(context.space_data.pin_id, bpy.types.ParticleSettings):
        return context.space_data.pin_id
    return None

One wonders why it doesn't use context.particle_settings. Since you are adding a new system, and quite likely not from the properties space will not use this.. moving on.

Other things to look for are the setting of a context pointer in a draw method, eg in this case something like

def draw(self, context):
    self.layout.context_pointer_set(
            "particle_settings",
            particle_get_settings(context)
            )
    self.layout.operator("boid.foo")

Not used here but another way to set a context member. THe operator "boid.foo" would use the context.particle_settings a returned from the method Not used in this case moving on...

Using the reference

In as much as you have checked for no particle systems before adding one, and referencing it as the zeroth time of the objects particle systems... Can instead get the particle system from the new modifiers reference.

>>> mod = C.object.modifiers.new("Foo", type='PARTICLE_SYSTEM')
>>> ps = mod.particle_system
>>> settings = ps.settings
>>> mod
bpy.data.objects['Cube'].modifiers["Foo"]

>>> ps
bpy.data.objects['Cube'].particle_systems["Foo"]

>>> settings
bpy.data.particles['Foo']

Setting to boids, adds two default rules separate and flock, in that order.

>>> settings.physics_type = 'BOIDS'
>>> settings.boids.states['State'].rules[:]
[bpy.data.particles['Foo'].rules["Separate"], bpy.data.particles['Foo'].rules["Flock"]]

Note that using settings.boids.active_boid_state.rule avoids the need for state name.

Finding the override.

A usual rule of thumb to find an override, armed with the big possibility that outside of properties area need to set one of the aforementioned particlish context members, can check using the operators poll method.

>>> override = {
...     "particle_system" : ps,
...     "particle_editable_system" : ps,
...     "particle_settings" : settings,
...     }


>>> bpy.ops.boid.rule_add.poll()
True

>>> bpy.ops.boid.rule_add()
{'CANCELLED'}

Which is a bummer, if there was a poll error could try polling against different context members... but alas in this instance the boid operators poll regardless.

>>> bpy.ops.boid.rule_add.poll(override)
True

>>> bpy.ops.boid.rule_add.poll({"snoo" : 'LUMP'})
True

Sheesh, not much luck, moving on

>>> bpy.ops.boid.rule_move_up(override)
{'FINISHED'}

At last, the Eureka moment of seeing 'FINISHED' indicating the operator has done its thing.

Cleaning the slate.

Ok, using the single context override as suggested by @lemon

May be simpler to remove the two default rules and rebuild rather than a list shuffle.

>>> while settings.boids.active_boid_state.rules:
...     bpy.ops.boid.rule_del({"particle_settings" : settings})
...     
{'FINISHED'}
{'FINISHED'}

Note, am of the opinion since 2.8 can pass only the overridden props to the operator.

Add the new rules in order.

Example. Add the new rules based on some data. If the rule is a goal, set the goal object to some previously set target object.

>>> state = settings.boids.active_boid_state
>>> rules = ('FLOCK', 'GOAL', 'FIGHT', 'FLOCK')
>>> for rule in rules:
...     bpy.ops.boid.rule_add({"particle_settings" : settings}, type=rule)
...     if rule == 'GOAL':
...         state.active_boid_rule.object = target_object
...     
{'FINISHED'}
{'FINISHED'}
{'FINISHED'}
{'FINISHED'}