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Mini Shell
import configparser
import dataclasses
from dataclasses import dataclass
from pathlib import Path
from typing import Callable
from typing import ClassVar
from typing import Optional
from typing import Union
from .helpers import make_path
class ConfigError(BaseException):
pass
class MissingConfig(ConfigError):
pass
class MissingConfigSection(ConfigError):
pass
class MissingConfigItem(ConfigError):
pass
class ConfigValueTypeError(ConfigError):
pass
class _GetterDispatch:
def __init__(self, initialdata, default_getter: Callable):
self.default_getter = default_getter
self.data = initialdata
def get_fn_for_type(self, type_):
return self.data.get(type_, self.default_getter)
def get_typed_value(self, type_, name):
get_fn = self.get_fn_for_type(type_)
return get_fn(name)
def _parse_cfg_file(filespec: Union[Path, str]):
cfg = configparser.ConfigParser()
try:
filepath = make_path(filespec, check_exists=True)
except FileNotFoundError as e:
raise MissingConfig(f"No config file found at {filespec}") from e
else:
with open(filepath, encoding="utf-8") as f:
cfg.read_file(f)
return cfg
def _build_getter(cfg_obj, cfg_section, method, converter=None):
def caller(option, **kwargs):
try:
rv = getattr(cfg_obj, method)(cfg_section, option, **kwargs)
except configparser.NoSectionError as nse:
raise MissingConfigSection(
f"No config section named {cfg_section}"
) from nse
except configparser.NoOptionError as noe:
raise MissingConfigItem(f"No config item for {option}") from noe
except ValueError as ve:
# ConfigParser.getboolean, .getint, .getfloat raise ValueError
# on bad types
raise ConfigValueTypeError(
f"Wrong value type for {option}"
) from ve
else:
if converter:
try:
rv = converter(rv)
except Exception as e:
raise ConfigValueTypeError(
f"Wrong value type for {option}"
) from e
return rv
return caller
def _build_getter_dispatch(cfg_obj, cfg_section, converters=None):
converters = converters or {}
default_getter = _build_getter(cfg_obj, cfg_section, "get")
# support ConfigParser builtins
getters = {
int: _build_getter(cfg_obj, cfg_section, "getint"),
bool: _build_getter(cfg_obj, cfg_section, "getboolean"),
float: _build_getter(cfg_obj, cfg_section, "getfloat"),
str: default_getter,
}
# use ConfigParser.get and convert value
getters.update(
{
type_: _build_getter(
cfg_obj, cfg_section, "get", converter=converter_fn
)
for type_, converter_fn in converters.items()
}
)
return _GetterDispatch(getters, default_getter)
@dataclass
class ReadsCfg:
section_header: ClassVar[str]
converters: ClassVar[Optional[dict]] = None
@classmethod
def from_cfg_file(cls, filespec: Union[Path, str]):
cfg = _parse_cfg_file(filespec)
dispatch = _build_getter_dispatch(
cfg, cls.section_header, converters=cls.converters
)
kwargs = {
field.name: dispatch.get_typed_value(field.type, field.name)
for field in dataclasses.fields(cls)
}
return cls(**kwargs)
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