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"""Abstract I/O mode container.
Mode strings are used in in `~fs.base.FS.open` and
`~fs.base.FS.openbin`.
"""
from __future__ import print_function, unicode_literals
import typing
from ._typing import Text
if typing.TYPE_CHECKING:
from typing import FrozenSet, Set, Union
__all__ = ["Mode", "check_readable", "check_writable", "validate_openbin_mode"]
# https://docs.python.org/3/library/functions.html#open
class Mode(typing.Container[Text]):
"""An abstraction for I/O modes.
A mode object provides properties that can be used to interrogate the
`mode strings <https://docs.python.org/3/library/functions.html#open>`_
used when opening files.
Example:
>>> mode = Mode('rb')
>>> mode.reading
True
>>> mode.writing
False
>>> mode.binary
True
>>> mode.text
False
"""
def __init__(self, mode):
# type: (Text) -> None
"""Create a new `Mode` instance.
Arguments:
mode (str): A *mode* string, as used by `io.open`.
Raises:
ValueError: If the mode string is invalid.
"""
self._mode = mode
self.validate()
def __repr__(self):
# type: () -> Text
return "Mode({!r})".format(self._mode)
def __str__(self):
# type: () -> Text
return self._mode
def __contains__(self, character):
# type: (object) -> bool
"""Check if a mode contains a given character."""
assert isinstance(character, Text)
return character in self._mode
def to_platform(self):
# type: () -> Text
"""Get a mode string for the current platform.
Currently, this just removes the 'x' on PY2 because PY2 doesn't
support exclusive mode.
"""
return self._mode
def to_platform_bin(self):
# type: () -> Text
"""Get a *binary* mode string for the current platform.
This removes the 't' and adds a 'b' if needed.
"""
_mode = self.to_platform().replace("t", "")
return _mode if "b" in _mode else _mode + "b"
def validate(self, _valid_chars=frozenset("rwxtab+")):
# type: (Union[Set[Text], FrozenSet[Text]]) -> None
"""Validate the mode string.
Raises:
ValueError: if the mode contains invalid chars.
"""
mode = self._mode
if not mode:
raise ValueError("mode must not be empty")
if not _valid_chars.issuperset(mode):
raise ValueError("mode '{}' contains invalid characters".format(mode))
if mode[0] not in "rwxa":
raise ValueError("mode must start with 'r', 'w', 'x', or 'a'")
if "t" in mode and "b" in mode:
raise ValueError("mode can't be binary ('b') and text ('t')")
def validate_bin(self):
# type: () -> None
"""Validate a mode for opening a binary file.
Raises:
ValueError: if the mode contains invalid chars.
"""
self.validate()
if "t" in self:
raise ValueError("mode must be binary")
@property
def create(self):
# type: () -> bool
"""`bool`: `True` if the mode would create a file."""
return "a" in self or "w" in self or "x" in self
@property
def reading(self):
# type: () -> bool
"""`bool`: `True` if the mode permits reading."""
return "r" in self or "+" in self
@property
def writing(self):
# type: () -> bool
"""`bool`: `True` if the mode permits writing."""
return "w" in self or "a" in self or "+" in self or "x" in self
@property
def appending(self):
# type: () -> bool
"""`bool`: `True` if the mode permits appending."""
return "a" in self
@property
def updating(self):
# type: () -> bool
"""`bool`: `True` if the mode permits both reading and writing."""
return "+" in self
@property
def truncate(self):
# type: () -> bool
"""`bool`: `True` if the mode would truncate an existing file."""
return "w" in self or "x" in self
@property
def exclusive(self):
# type: () -> bool
"""`bool`: `True` if the mode require exclusive creation."""
return "x" in self
@property
def binary(self):
# type: () -> bool
"""`bool`: `True` if a mode specifies binary."""
return "b" in self
@property
def text(self):
# type: () -> bool
"""`bool`: `True` if a mode specifies text."""
return "t" in self or "b" not in self
def check_readable(mode):
# type: (Text) -> bool
"""Check a mode string allows reading.
Arguments:
mode (str): A mode string, e.g. ``"rt"``
Returns:
bool: `True` if the mode allows reading.
"""
return Mode(mode).reading
def check_writable(mode):
# type: (Text) -> bool
"""Check a mode string allows writing.
Arguments:
mode (str): A mode string, e.g. ``"wt"``
Returns:
bool: `True` if the mode allows writing.
"""
return Mode(mode).writing
def validate_open_mode(mode):
# type: (Text) -> None
"""Check ``mode`` parameter of `~fs.base.FS.open` is valid.
Arguments:
mode (str): Mode parameter.
Raises:
`ValueError` if mode is not valid.
"""
Mode(mode)
def validate_openbin_mode(mode, _valid_chars=frozenset("rwxab+")):
# type: (Text, Union[Set[Text], FrozenSet[Text]]) -> None
"""Check ``mode`` parameter of `~fs.base.FS.openbin` is valid.
Arguments:
mode (str): Mode parameter.
Raises:
`ValueError` if mode is not valid.
"""
if "t" in mode:
raise ValueError("text mode not valid in openbin")
if not mode:
raise ValueError("mode must not be empty")
if mode[0] not in "rwxa":
raise ValueError("mode must start with 'r', 'w', 'a' or 'x'")
if not _valid_chars.issuperset(mode):
raise ValueError("mode '{}' contains invalid characters".format(mode))
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