laboneq.workflow.reference

Module for workflow reference.

notset = object() module-attribute

Reference(ref, default=notset)

A reference class.

A Reference is a placeholder for objects used while a workflow graph is being constructed.

If tasks are the nodes in the workflow graph, then references define the edges.

For example, in a workflow definition like:

@workflow
def add_and_multiply(a, b):
    c = add_task(a, 2)
    d = multiply_task(c, 3)

the values a, b, c and d are all references. By tracking where references are used, the graph builder can determine how inputs and outputs are passed between tasks in the graph.

References also track some Python operations performed on them, so one can also use references like a["value"]. This creates a reference for "the item named 'value' from reference 'a'".

When a workflow graph is run, the references are used to determine the input values to the next task from the outputs returned by the earlier tasks.

The following operations are supported

• getitem()
• getattr()
• eq()

Notes on specific Python operations

Equality comparison

For equality comparison, especially with booleans, use == instead of is. Equality with is will always return False.

Parameters:

Name	Type	Description	Default
ref	object	An object this reference points to.	required
default	object	Default value of ref.	notset

add_overwrite(one, other)

Add an overwrite to an reference.

are_equal(one, other)

Check if two references are equal.

get_default(reference)

Get reference default value.

get_ref(reference)

Return an object the reference points to.

resolve_to_value(ref, states, *, only_ref=False)

Resolve reference.

The resolve order is following:

* Look value from `states`
* Iterate over overwritten values and return the first one that
    exists in `states` or is constant

Parameters:

Name	Type	Description	Default
ref	Reference	Root reference	required
states	dict	A mapping of reference to actual values	required
only_ref	bool	Check only the root reference	False

Raises:

Type	Description
WorkflowError	Value cannot be resolved.

unwrap(reference, value)

Unwrap the reference and any operations done on it.