Conditions/Transitions¶

Conditions represent choices to move between actions – these are read by the application builder when executing the graph. Note that these will always be specified in order – the first condition that evaluates to True will be the selected action.

class burr.core.action.Condition(
keys: List[str],
resolver: Callable[[State], bool],
name: str = None,
optional_keys: List[str] = None,
)¶
__init__(
keys: List[str],
resolver: Callable[[State], bool],
name: str = None,
optional_keys: List[str] = None,
)¶

Base condition class. Chooses keys to read from the state and a resolver function. If you want a condition that defaults to true, use Condition.default or just default.

Note that you can use a few fundamental operators to build more complex conditions:

  • ~ operator allows you to automatically invert the condition.

  • | operator allows you to OR two conditions together.

  • & operator allows you to AND two conditions together.

Parameters:

  • keys – Keys to read from the state

  • resolver – Function to resolve the condition to True or False

  • name – Name of the condition

__and__(other: Condition) → Condition¶

Combines two conditions with an AND operator. This will return a new condition that is the AND of the two conditions.

To check if both foo is bar and baz is qux:

condition = Condition.when(foo="bar") & Condition.when(baz="qux")
# equivalent to
condition = Condition.when(foo="bar", baz="qux")
Parameters:

other – Other condition to AND with

Returns:

A new condition that is the AND of the two conditions

__or__(other: Condition) → Condition¶

Combines two conditions with an OR operator. This will return a new condition that is the OR of the two conditions.

To check if either foo is bar or baz is qux:

condition = Condition.when(foo="bar") | Condition.when(baz="qux")
Parameters:

other – Other condition to OR with

Returns:

A new condition that is the OR of the two conditions

static expr(expr: str) → Condition¶

Returns a condition that evaluates the given expression. Expression must use only state variables and Python operators. Do not trust that anything else will work.

Do not accept expressions generated from user-inputted text, this has the potential to be unsafe.

You can also refer to this as from burr.core import expr in the API.

Parameters:

expr – Expression to evaluate

Returns:

A condition that evaluates the given expression

static lmda(
resolver: Callable[[State], bool],
state_keys: List[str],
) → Condition¶

Returns a condition that evaluates the given function of State. Note that this is just a simple wrapper over the Condition object.

This does not (yet) support optional (default) arguments.

Parameters:

  • fn

  • state_keys

Returns:

property reads: list[str]¶

Returns the keys from the state that this function reads

Returns:

A list of keys

run(state: State, **run_kwargs) → dict¶

Runs the function on the given state and returns the result. The result is just a key/value dictionary.

Parameters:

  • state – State to run the function on

  • run_kwargs – Additional arguments to the function passed at runtime.

Returns:

Result of the function

classmethod when(**kwargs)¶

Returns a condition that checks if the given keys are in the state and equal to the given values.

You can also refer to this as from burr.core import when in the API.

Parameters:

kwargs – Keyword arguments of keys and values to check – will be an AND condition

Returns:

A condition that checks if the given keys are in the state and equal to the given values