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import re |
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from abc import ABCMeta, abstractmethod |
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from typing import Iterator, Mapping, Optional, Pattern |
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_posix_variable: Pattern[str] = re.compile( |
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r""" |
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\$\{ |
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(?P<name>[^\}:]*) |
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(?::- |
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(?P<default>[^\}]*) |
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)? |
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\} |
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""", |
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re.VERBOSE, |
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) |
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class Atom(metaclass=ABCMeta): |
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def __ne__(self, other: object) -> bool: |
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result = self.__eq__(other) |
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if result is NotImplemented: |
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return NotImplemented |
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return not result |
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@abstractmethod |
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def resolve(self, env: Mapping[str, Optional[str]]) -> str: ... |
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class Literal(Atom): |
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def __init__(self, value: str) -> None: |
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self.value = value |
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def __repr__(self) -> str: |
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return f"Literal(value={self.value})" |
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def __eq__(self, other: object) -> bool: |
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if not isinstance(other, self.__class__): |
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return NotImplemented |
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return self.value == other.value |
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def __hash__(self) -> int: |
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return hash((self.__class__, self.value)) |
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def resolve(self, env: Mapping[str, Optional[str]]) -> str: |
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return self.value |
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class Variable(Atom): |
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def __init__(self, name: str, default: Optional[str]) -> None: |
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self.name = name |
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self.default = default |
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def __repr__(self) -> str: |
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return f"Variable(name={self.name}, default={self.default})" |
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def __eq__(self, other: object) -> bool: |
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if not isinstance(other, self.__class__): |
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return NotImplemented |
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return (self.name, self.default) == (other.name, other.default) |
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def __hash__(self) -> int: |
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return hash((self.__class__, self.name, self.default)) |
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def resolve(self, env: Mapping[str, Optional[str]]) -> str: |
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default = self.default if self.default is not None else "" |
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result = env.get(self.name, default) |
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return result if result is not None else "" |
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def parse_variables(value: str) -> Iterator[Atom]: |
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cursor = 0 |
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for match in _posix_variable.finditer(value): |
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(start, end) = match.span() |
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name = match["name"] |
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default = match["default"] |
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if start > cursor: |
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yield Literal(value=value[cursor:start]) |
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yield Variable(name=name, default=default) |
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cursor = end |
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length = len(value) |
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if cursor < length: |
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yield Literal(value=value[cursor:length]) |
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