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import abc
import io
import itertools
import os
import pathlib
from typing import Any, BinaryIO, Iterable, Iterator, NoReturn, Text, Optional
from typing import runtime_checkable, Protocol
from typing import Union
StrPath = Union[str, os.PathLike[str]]
__all__ = ["ResourceReader", "Traversable", "TraversableResources"]
class ResourceReader(metaclass=abc.ABCMeta):
"""Abstract base class for loaders to provide resource reading support."""
@abc.abstractmethod
def open_resource(self, resource: Text) -> BinaryIO:
"""Return an opened, file-like object for binary reading.
The 'resource' argument is expected to represent only a file name.
If the resource cannot be found, FileNotFoundError is raised.
"""
# This deliberately raises FileNotFoundError instead of
# NotImplementedError so that if this method is accidentally called,
# it'll still do the right thing.
raise FileNotFoundError
@abc.abstractmethod
def resource_path(self, resource: Text) -> Text:
"""Return the file system path to the specified resource.
The 'resource' argument is expected to represent only a file name.
If the resource does not exist on the file system, raise
FileNotFoundError.
"""
# This deliberately raises FileNotFoundError instead of
# NotImplementedError so that if this method is accidentally called,
# it'll still do the right thing.
raise FileNotFoundError
@abc.abstractmethod
def is_resource(self, path: Text) -> bool:
"""Return True if the named 'path' is a resource.
Files are resources, directories are not.
"""
raise FileNotFoundError
@abc.abstractmethod
def contents(self) -> Iterable[str]:
"""Return an iterable of entries in `package`."""
raise FileNotFoundError
class TraversalError(Exception):
pass
@runtime_checkable
class Traversable(Protocol):
"""
An object with a subset of pathlib.Path methods suitable for
traversing directories and opening files.
Any exceptions that occur when accessing the backing resource
may propagate unaltered.
"""
@abc.abstractmethod
def iterdir(self) -> Iterator["Traversable"]:
"""
Yield Traversable objects in self
"""
def read_bytes(self) -> bytes:
"""
Read contents of self as bytes
"""
with self.open('rb') as strm:
return strm.read()
def read_text(self, encoding: Optional[str] = None) -> str:
"""
Read contents of self as text
"""
with self.open(encoding=encoding) as strm:
return strm.read()
@abc.abstractmethod
def is_dir(self) -> bool:
"""
Return True if self is a directory
"""
@abc.abstractmethod
def is_file(self) -> bool:
"""
Return True if self is a file
"""
def joinpath(self, *descendants: StrPath) -> "Traversable":
"""
Return Traversable resolved with any descendants applied.
Each descendant should be a path segment relative to self
and each may contain multiple levels separated by
``posixpath.sep`` (``/``).
"""
if not descendants:
return self
names = itertools.chain.from_iterable(
path.parts for path in map(pathlib.PurePosixPath, descendants)
)
target = next(names)
matches = (
traversable for traversable in self.iterdir() if traversable.name == target
)
try:
match = next(matches)
except StopIteration:
raise TraversalError(
"Target not found during traversal.", target, list(names)
)
return match.joinpath(*names)
def __truediv__(self, child: StrPath) -> "Traversable":
"""
Return Traversable child in self
"""
return self.joinpath(child)
@abc.abstractmethod
def open(self, mode='r', *args, **kwargs):
"""
mode may be 'r' or 'rb' to open as text or binary. Return a handle
suitable for reading (same as pathlib.Path.open).
When opening as text, accepts encoding parameters such as those
accepted by io.TextIOWrapper.
"""
@abc.abstractproperty
def name(self) -> str:
"""
The base name of this object without any parent references.
"""
class TraversableResources(ResourceReader):
"""
The required interface for providing traversable
resources.
"""
@abc.abstractmethod
def files(self) -> "Traversable":
"""Return a Traversable object for the loaded package."""
def open_resource(self, resource: StrPath) -> io.BufferedReader:
return self.files().joinpath(resource).open('rb')
def resource_path(self, resource: Any) -> NoReturn:
raise FileNotFoundError(resource)
def is_resource(self, path: StrPath) -> bool:
return self.files().joinpath(path).is_file()
def contents(self) -> Iterator[str]:
return (item.name for item in self.files().iterdir())
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