How to use ordered transitions with conditions

[schaefer01]

Again, perhaps I am coding this wrong without understanding the true behavior.

The section on the main page is titled "ordered transitions"

My assumption is, I am checking for transitions that cannot occur, but they do occur.

Perhaps I could use an example showing how the check operation behaves when bad behavior does occur?

the code:

states = ['A', 'B', 'C']
machine = Machine(states=states, initial='A')
machine.add_ordered_transitions(['A', 'C', 'B'])
machine.add_ordered_transitions(conditions=['check_A2B','check_C2A','check_B2C'])
print(machine.state)

A
machine.next_state()
True
print(machine.state)
C
machine.next_state()
True
print(machine.state)
B
machine.next_state()
True
print(machine.state)
A

[aleneum]

Hello @schaefer01,

machine.add_ordered_transitions(['A', 'C', 'B']) will create ordered transitions from A -next_state-> C -next_state-> B and a cyclic back reference to A. The second call machine.add_ordered_transitions(conditions=['check_A2B','check_C2A','check_B2C']) will not use the previously created transitions but create a set of new ones. The documentations states:

states : list - A list of state names defining the order of the transitions. E.g., ['A', 'B', 'C'] will generate transitions for A --> B, B --> C, and C --> A (if loop is True). If states is None, all states in the current instance will be used.

So, transitions will create transitions A -next_state[check_A2B]-> B -next_state[check_C2A]-> C -next_state[check_B2C]-> A but none of them will actually be evaluated since your first set of transitions will always be succesfull. What you probably want to do is pass conditions and state order at the same call.

from transitions import Machine

class Model:

    def check_A2C(self):
        return True
    
    def check_C2B(self):
        return True
    
    def check_B2A(self):
        return False

model = Model()
machine = Machine(model, states=["A", "B", "C"], initial="A")
machine.add_ordered_transitions(
    ["A", "C", "B"], conditions=["check_A2C", "check_C2B", "check_B2A"]
)
assert model.is_A()
assert model.next_state()
assert model.is_C()
assert model.next_state()
assert model.is_B()
assert not model.next_state() # transition unsucessful
assert model.is_B()  # we are still in B since check_B2A failed

[schaefer01]

Thank you.
I understand how it is easier to document proper use than to predict and document all the possible ways new developers can misunderstand and do the wrong thing.