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# standard imports
import typing
# bsie imports
from bsie.utils import bsfs, errors, safe_load, unpack_qualified_name
# inner-module imports
from . import base
# exports
__all__: typing.Sequence[str] = (
'ExtractorBuilder',
)
## code ##
class ExtractorBuilder():
"""Build `bsie.base.Extractor instances.
It is permissible to build multiple instances of the same extractor
(typically with different arguments), hence the ExtractorBuilder
receives a list of build specifications. Each specification is
a dict with a single key (extractor's qualified name) and a dict
to be used as keyword arguments.
Example: [{'bsie.extractor.generic.path.Path': {}}, ]
"""
# build specifications
_specs: typing.List[typing.Dict[str, typing.Dict[str, typing.Any]]]
def __init__(self, specs: typing.List[typing.Dict[str, typing.Dict[str, typing.Any]]]):
self._specs = specs
def __iter__(self) -> typing.Iterator[int]:
"""Iterate over extractor specifications."""
return iter(range(len(self._specs)))
def build(self, index: int) -> base.Extractor:
"""Return an instance of the n'th extractor (n=*index*)."""
# get build instructions
specs = self._specs[index]
# check specs structure. expecting[{name: {kwargs}}]
if not isinstance(specs, dict):
raise TypeError(f'expected a dict, found {bsfs.typename(specs)}')
if len(specs) != 1:
raise TypeError(f'expected a dict of length one, found {len(specs)}')
# get name and args from specs
name = next(iter(specs.keys()))
kwargs = specs[name]
# check kwargs structure
if not isinstance(kwargs, dict):
raise TypeError(f'expected a dict, found {bsfs.typename(kwargs)}')
# check name and get module/class components
module_name, class_name = unpack_qualified_name(name)
# import extractor class
cls = safe_load(module_name, class_name)
try: # build and return instance
return cls(**kwargs)
except Exception as err:
raise errors.BuilderError(f'failed to build extractor {name} due to {bsfs.typename(err)}: {err}') from err
## EOF ##
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