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