[ allennlp.common.from_params ]
T = TypeVar("T", bound="FromParams")
def takes_arg(obj, arg: str) -> bool
Checks whether the provided obj takes a certain arg. If it's a class, we're really checking whether its constructor does. If it's a function or method, we're checking the object itself. Otherwise, we raise an error.
def takes_kwargs(obj) -> bool
Checks whether a provided object takes in any positional arguments. Similar to takes_arg, we do this for both the init function of the class or a function / method Otherwise, we raise an error
def can_construct_from_params(type_: Type) -> bool
def is_base_registrable(cls) -> bool
Checks whether this is a class that directly inherits from Registrable, or is a subclass of such a class.
def remove_optional(annotation: type)
Optional[X] annotations are actually represented as Union[X, NoneType]. For our purposes, the "Optional" part is not interesting, so here we throw it away.
def infer_params( cls: Type[T], constructor: Callable[..., T] = None )
def create_kwargs( constructor: Callable[..., T], cls: Type[T], params: Params, **extras ) -> Dict[str, Any]
Given some class, a
Params object, and potentially other keyword arguments,
create a dict of keyword args suitable for passing to the class's constructor.
The function does this by finding the class's constructor, matching the constructor
arguments to entries in the
params object, and instantiating values for the parameters
using the type annotation and possibly a from_params method.
Any values that are provided in the
extras will just be used as is.
For instance, you might provide an existing
Vocabulary this way.
def create_extras( cls: Type[T], extras: Dict[str, Any] ) -> Dict[str, Any]
Given a dictionary of extra arguments, returns a dictionary of kwargs that actually are a part of the signature of the cls.from_params (or cls) method.
def pop_and_construct_arg( class_name: str, argument_name: str, annotation: Type, default: Any, params: Params, **extras ) -> Any
Does the work of actually constructing an individual argument for
Here we're in the inner loop of iterating over the parameters to a particular constructor,
trying to construct just one of them. The information we get for that parameter is its name,
its type annotation, and its default value; we also get the full set of
constructing the object (which we may mutate), and any
extras that the constructor might
We take the type annotation and default value here separately, instead of using an
inspect.Parameter object directly, so that we can handle
Union types using recursion on
this method, trying the different annotation types in the union in turn.
def construct_arg( class_name: str, argument_name: str, popped_params: Params, annotation: Type, default: Any, **extras ) -> Any
The first two parameters here are only used for logging if we encounter an error.
Mixin to give a from_params method to classes. We create a distinct base class for this because sometimes we want non-Registrable classes to be instantiatable from_params.
class FromParams: | ... | @classmethod | def from_params( | cls: Type[T], | params: Params, | constructor_to_call: Callable[..., T] = None, | constructor_to_inspect: Callable[..., T] = None, | **extras | ) -> T
This is the automatic implementation of
from_params. Any class that subclasses
Registrable, which itself subclasses
FromParams) gets this
implementation for free. If you want your class to be instantiated from params in the
"obvious" way -- pop off parameters and hand them to your constructor with the same names --
this provides that functionality.
If you need more complex logic in your from
from_params method, you'll have to implement
your own method that overrides this one.
constructor_to_inspect arguments deal with a bit of
redirection that we do. We allow you to register particular
@classmethods on a class as
the constructor to use for a registered name. This lets you, e.g., have a single
Vocabulary class that can be constructed in two different ways, with different names
registered to each constructor. In order to handle this, we need to know not just the class
we're trying to construct (
cls), but also what method we should inspect to find its
constructor_to_inspect), and what method to call when we're done constructing
constructor_to_call). These two methods are the same when you've used a
@classmethod as your constructor, but they are
different when you use the default
constructor (because you inspect
__init__, but call