Version: Next

Interfaces

MAGDA interfaces are not strict interfaces known from programming languages but classes encapsulating results that are passed between modules. They can be understood as a data contract. However, the main concept is still similar to real interfaces - it is a way to accept multiple predecessors of a module that returns a result of the same data type.

Idea#

An exemplary use case is when a given module is preceded by different modules having different logic in every experiment pipeline, but always expecting the same data type. A solution for that could be to assign a common interface for predecessors' results and accept such interface as input in the given module. See the example below:

TeapotModule accepts predecessors returning TeaLeaves. Alternative types of tea, that can be used in separate runtimes, have to produce results exactly of the same kind.

Interfaces can be defined as easily as:

from magda.module.module import Module
# Common interfaceclass TeaLeaves(Module.Interface):    ...
# Types of tea in alphabetical order@register('black-tea')@produce(TeaLeaves)@finalizeclass BlackTeaGetter(Module.Runtime):    def run(self, *args, **kwargs):        ...
@register('green-tea')@produce(TeaLeaves)@finalizeclass GreenTeaGetter(Module.Runtime):    def run(self, *args, **kwargs):        ...
@register('white-tea')@produce(TeaLeaves)@finalizeclass WhiteTeaGetter(Module.Runtime):    def run(self, *args, **kwargs):        ...
# Final module@register('teapot')@accept(TeaLeaves)@finalizeclass TeapotModule(Module.Runtime):    def run(self, *args, **kwargs):        ...

An interface has to inherit from the Module.Interface class. TeapotModule implements Module.Runtime, which can take as its input only modules that produce results coherent with the data type it accepts (in this case TeaLeaves). This has to be defined using the @accept decorator before the definition of TeapotModule and the @produce decorator in tea getters.

A following, YAML configuration file is consistent with the example above and is a valid pipeline structure:

modules:  - name: tea-getter    type: green-tea
  - name: small-teapot    type: teapot    depends_on:      - tea-getter

Modules: tea-getter is of type GreenTeaGetter, that produces a correct data interface (TeaLeaves), which is acceptable by TeapotModule. That is why it can be a valid predecessor of small-teapot.

Decorator `@produce`#

We use @produce decorator above the definition of a class in order to specify the interface of the module's output. The @produce decorator may accept only a single interface and the result returned in this module's run function always has to be of that interface. @produce will be described in detail in the section devoted to Modules. Below you can see a correct definition of a submodule.

@produce(CorrectDataInterface)@finalizeclass Submodule(Module.Runtime):    def run(self, *args, **kwargs):        important_string = 'This is important'        # some logic happens here        return CorrectDataInterface(important_string)

Submodule should produce a result of type CorrectDataInterface, which is done in the run function.

Do all single values have to be encapsulated in interfaces?#

When the @produce decorator is not defined, a module can return a value of any type, as shown below:

@finalizeclass Submodule(Module.Runtime):    def run(self, *args, **kwargs):        important_magic_integer = 7        # some logic happens here        return important_magic_integer

However, when @produce decorator was defined, even a value of primitive type has to be encapsulated in an interface. In such a case, this is the only valid data contract in MAGDA. Even if it is a float or an integer, it has to be enclosed within an object.

@produce(CustomInteger)@finalizeclass Submodule(Module.Runtime):    def run(self, *args, **kwargs):        important_magic_integer = 7        # some logic happens here        return CustomInteger(important_magic_integer)

Examples of incorrect usage#

Please, have a look at the following examples that are incorrect.

A module cannot produce multiple interfaces:

@produce(CorrectInterface, AdditionalCorrectInterface) # Wrong: should be just one argument@finalizeclass ModuleIncorrectSample(Module.Runtime):    ...

A module cannot produce not an interface (i.e. another module):

@finalizeclass CorrectAnotherModule(Module.Runtime):    ...
@produce(CorrectAnotherModule) # Wrong: should be a class inheriting from ModuleInterface@finalizeclass ModuleSample(Module.Runtime):    ...

A module cannot produce an interface that is not inheriting from ModuleInterface:

class IncorrectInterface(ABC):    ...
@produce(IncorrectInterface) # Wrong: should be a class inheriting from ModuleInterface@finalizeclass ModuleIncorrectSample(Module.Runtime):    ...

A module cannot produce null or empty interface:

@produce(None)  # Wrong: should be an interface@finalizeclass ModuleIncorrectSample(Module.Runtime):    ...
@produce()  # Wrong: should be skipped@finalizeclass ModuleIncorrectAnotherSample(Module.Runtime):    ...

A correct advanced example#

Below you can find a more complicated, correct example for an imaginary pipeline of making a Caffè Americano. For details and questions related to accessing results from concrete modules by their interfaces, refer to Modules.

from magda.decorators import register, finalize, accept, produce, exposefrom magda.module import Module
class Liquid(Module.Interface):    def __init__(self, liquid_type: str, volume: str):        self.liquid_type = liquid_type        self.volume = volume
@register('coffee-machine-dispenser')@produce(Liquid)@finalizeclass CoffeeMachineDispenser(Module.Runtime):    def run(self, data, request, *args, **kwargs):        coffee_type = self.shared_parameters['coffee']        liquid_type = self.parameters['liquid']        # Returns agreed (@produce) interface        return Liquid(            liquid_type=liquid_type,            volume=self.get_volume(coffee_type, request),        )
@register('mug')@accept(Liquid)@finalizeclass Mug(Module.Runtime):    def run(self, data, *args, **kwargs):        parts = data.of(Liquid)  # the results of modules producing liquids        fluid_mechanics = self.context['fluid-mechanics']        content = fluid_mechanics.mix(parts)        return content

modules:  - name: coffee-dispenser    type: coffee-machine-dispenser    parameters:      liquid: coffee
  - name: water-dispenser    type: coffee-machine-dispenser    parameters:      liquid: water
  - name: coding-mug    type: mug    expose: caffe-americano    depends_on:      - coffee-dispenser      - water-dispenser
shared_parameters:  coffee: americano

Idea#

Decorator @produce#

Do all single values have to be encapsulated in interfaces?#

Examples of incorrect usage#

A correct advanced example#

Decorator `@produce`#