# Conditions

Regular events fire only when a channel *changes* state. A condition, in contrast, is
evaluated when a state is entered: if the configured channel (or global timer) is
already in the specified state, the corresponding `Condition{N}` event fires
immediately. This allows states to be skipped based on the current state of a channel
rather than waiting for a change to occur.

In this example, Condition2 is met while `Port2` is high. If that is the case when
the state Port2Light is entered, the `Condition2` event fires and the state
machine advances to Port3Light without waiting for the one-second state timer to
expire.

![image](state_machines/examples/conditions__light.svg)![image](state_machines/examples/conditions__dark.svg)

### Python

```python
from bpod_core.fsm import StateMachine

fsm = StateMachine()

fsm.set_condition(
    index=2,
    channel='Port2',
    value=True,  # condition is true when Port2 is high
)

fsm.add_state(
    name='Port1Light',
    timer=1,
    transitions={'Tup': 'Port2Light'},
    actions={'PWM1': 255},
)
fsm.add_state(
    name='Port2Light',
    timer=1,
    transitions={'Tup': 'Port3Light', 'Condition2': 'Port3Light'},
    actions={'PWM2': 255},
)
fsm.add_state(
    name='Port3Light',
    timer=1,
    transitions={'Tup': '>exit'},
    actions={'PWM3': 255},
)
```

### JSON

```json
{
  "states": {
    "Port1Light": {
      "timer": 1.0,
      "transitions": {
        "Tup": "Port2Light"
      },
      "actions": {
        "PWM1": 255
      }
    },
    "Port2Light": {
      "timer": 1.0,
      "transitions": {
        "Tup": "Port3Light",
        "Condition2": "Port3Light"
      },
      "actions": {
        "PWM2": 255
      }
    },
    "Port3Light": {
      "timer": 1.0,
      "transitions": {
        "Tup": ">exit"
      },
      "actions": {
        "PWM3": 255
      }
    }
  },
  "conditions": {
    "2": {
      "channel": "Port2",
      "value": true
    }
  }
}
```

### YAML

```yaml
states:
  Port1Light:
    timer: 1.0
    transitions:
      Tup: Port2Light
    actions:
      PWM1: 255
  Port2Light:
    timer: 1.0
    transitions:
      Tup: Port3Light
      Condition2: Port3Light
    actions:
      PWM2: 255
  Port3Light:
    timer: 1.0
    transitions:
      Tup: '>exit'
    actions:
      PWM3: 255
conditions:
  2:
    channel: Port2
    value: true
```