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