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config.py
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config.py
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import os
import typing
from collections.abc import MutableMapping
from pathlib import Path
class undefined:
pass
class EnvironError(Exception):
pass
class Environ(MutableMapping):
def __init__(self, environ: typing.MutableMapping = os.environ):
self._environ = environ
self._has_been_read: typing.Set[typing.Any] = set()
def __getitem__(self, key: typing.Any) -> typing.Any:
self._has_been_read.add(key)
return self._environ.__getitem__(key)
def __setitem__(self, key: typing.Any, value: typing.Any) -> None:
if key in self._has_been_read:
raise EnvironError(
f"Attempting to set environ['{key}'], but the value has already been "
"read."
)
self._environ.__setitem__(key, value)
def __delitem__(self, key: typing.Any) -> None:
if key in self._has_been_read:
raise EnvironError(
f"Attempting to delete environ['{key}'], but the value has already "
"been read."
)
self._environ.__delitem__(key)
def __iter__(self) -> typing.Iterator:
return iter(self._environ)
def __len__(self) -> int:
return len(self._environ)
environ = Environ()
class Config:
def __init__(
self,
env_file: typing.Union[str, Path] = None,
environ: typing.Mapping[str, str] = environ,
) -> None:
self.environ = environ
self.file_values: typing.Dict[str, str] = {}
if env_file is not None and os.path.isfile(env_file):
self.file_values = self._read_file(env_file)
def __call__(
self, key: str, cast: typing.Callable = None, default: typing.Any = undefined
) -> typing.Any:
return self.get(key, cast, default)
def get(
self, key: str, cast: typing.Callable = None, default: typing.Any = undefined
) -> typing.Any:
if key in self.environ:
value = self.environ[key]
return self._perform_cast(key, value, cast)
if key in self.file_values:
value = self.file_values[key]
return self._perform_cast(key, value, cast)
if default is not undefined:
return self._perform_cast(key, default, cast)
raise KeyError(f"Config '{key}' is missing, and has no default.")
def _read_file(self, file_name: typing.Union[str, Path]) -> typing.Dict[str, str]:
file_values: typing.Dict[str, str] = {}
with open(file_name) as input_file:
for line in input_file.readlines():
line = line.strip()
if "=" in line and not line.startswith("#"):
key, value = line.split("=", 1)
key = key.strip()
value = value.strip().strip("\"'")
file_values[key] = value
return file_values
def _perform_cast(
self, key: str, value: typing.Any, cast: typing.Callable = None
) -> typing.Any:
if cast is None or value is None:
return value
elif cast is bool and isinstance(value, str):
mapping = {"true": True, "1": True, "false": False, "0": False}
value = value.lower()
if value not in mapping:
raise ValueError(
f"Config '{key}' has value '{value}'. Not a valid bool."
)
return mapping[value]
try:
return cast(value)
except (TypeError, ValueError):
raise ValueError(
f"Config '{key}' has value '{value}'. Not a valid {cast.__name__}."
)