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61 lines
1.3 KiB
Python
61 lines
1.3 KiB
Python
import contextlib
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import enum
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import os
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from typing import NamedTuple
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from typing import Tuple
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from typing import Union
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class _Unset(enum.Enum):
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UNSET = 1
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UNSET = _Unset.UNSET
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class Var(NamedTuple):
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name: str
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default: str = ''
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SubstitutionT = Tuple[Union[str, Var], ...]
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ValueT = Union[str, _Unset, SubstitutionT]
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PatchesT = Tuple[Tuple[str, ValueT], ...]
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def format_env(parts, env):
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return ''.join(
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env.get(part.name, part.default) if isinstance(part, Var) else part
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for part in parts
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)
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@contextlib.contextmanager
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def envcontext(patch, _env=None):
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"""In this context, `os.environ` is modified according to `patch`.
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`patch` is an iterable of 2-tuples (key, value):
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`key`: string
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`value`:
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- string: `environ[key] == value` inside the context.
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- UNSET: `key not in environ` inside the context.
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- template: A template is a tuple of strings and Var which will be
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replaced with the previous environment
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"""
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env = os.environ if _env is None else _env
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before = env.copy()
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for k, v in patch:
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if v is UNSET:
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env.pop(k, None)
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elif isinstance(v, tuple):
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env[k] = format_env(v, before)
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else:
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env[k] = v
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try:
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yield
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finally:
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env.clear()
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env.update(before)
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