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2683 lines (2240 loc) · 90.7 KB
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"""
Python implementation of the io module.
"""
import os
import abc
import codecs
import errno
import stat
import sys
# Import _thread instead of threading to reduce startup cost
from _thread import allocate_lock as Lock
if sys.platform in {'win32', 'cygwin'}:
from msvcrt import setmode as _setmode
else:
_setmode = None
import io
from io import (__all__, SEEK_SET, SEEK_CUR, SEEK_END)
valid_seek_flags = {0, 1, 2} # Hardwired values
if hasattr(os, 'SEEK_HOLE') :
valid_seek_flags.add(os.SEEK_HOLE)
valid_seek_flags.add(os.SEEK_DATA)
# open() uses st_blksize whenever we can
DEFAULT_BUFFER_SIZE = 8 * 1024 # bytes
# NOTE: Base classes defined here are registered with the "official" ABCs
# defined in io.py. We don't use real inheritance though, because we don't want
# to inherit the C implementations.
# Rebind for compatibility
BlockingIOError = BlockingIOError
# Does open() check its 'errors' argument?
_CHECK_ERRORS = (hasattr(sys, "gettotalrefcount") or sys.flags.dev_mode)
def text_encoding(encoding, stacklevel=2):
"""
A helper function to choose the text encoding.
When encoding is not None, this function returns it.
Otherwise, this function returns the default text encoding
(i.e. "locale" or "utf-8" depends on UTF-8 mode).
This function emits an EncodingWarning if *encoding* is None and
sys.flags.warn_default_encoding is true.
This can be used in APIs with an encoding=None parameter
that pass it to TextIOWrapper or open.
However, please consider using encoding="utf-8" for new APIs.
"""
if encoding is None:
if sys.flags.utf8_mode:
encoding = "utf-8"
else:
encoding = "locale"
if sys.flags.warn_default_encoding:
import warnings
warnings.warn("'encoding' argument not specified.",
EncodingWarning, stacklevel + 1)
return encoding
# Wrapper for builtins.open
#
# Trick so that open() won't become a bound method when stored
# as a class variable (as dbm.dumb does).
#
# See init_set_builtins_open() in Python/pylifecycle.c.
@staticmethod
def open(file, mode="r", buffering=-1, encoding=None, errors=None,
newline=None, closefd=True, opener=None):
r"""Open file and return a stream. Raise OSError upon failure.
file is either a text or byte string giving the name (and the path
if the file isn't in the current working directory) of the file to
be opened or an integer file descriptor of the file to be
wrapped. (If a file descriptor is given, it is closed when the
returned I/O object is closed, unless closefd is set to False.)
mode is an optional string that specifies the mode in which the file is
opened. It defaults to 'r' which means open for reading in text mode. Other
common values are 'w' for writing (truncating the file if it already
exists), 'x' for exclusive creation of a new file, and 'a' for appending
(which on some Unix systems, means that all writes append to the end of the
file regardless of the current seek position). In text mode, if encoding is
not specified the encoding used is platform dependent. (For reading and
writing raw bytes use binary mode and leave encoding unspecified.) The
available modes are:
========= ===============================================================
Character Meaning
--------- ---------------------------------------------------------------
'r' open for reading (default)
'w' open for writing, truncating the file first
'x' create a new file and open it for writing
'a' open for writing, appending to the end of the file if it exists
'b' binary mode
't' text mode (default)
'+' open a disk file for updating (reading and writing)
========= ===============================================================
The default mode is 'rt' (open for reading text). For binary random
access, the mode 'w+b' opens and truncates the file to 0 bytes, while
'r+b' opens the file without truncation. The 'x' mode implies 'w' and
raises an `FileExistsError` if the file already exists.
Python distinguishes between files opened in binary and text modes,
even when the underlying operating system doesn't. Files opened in
binary mode (appending 'b' to the mode argument) return contents as
bytes objects without any decoding. In text mode (the default, or when
't' is appended to the mode argument), the contents of the file are
returned as strings, the bytes having been first decoded using a
platform-dependent encoding or using the specified encoding if given.
buffering is an optional integer used to set the buffering policy.
Pass 0 to switch buffering off (only allowed in binary mode), 1 to select
line buffering (only usable in text mode), and an integer > 1 to indicate
the size of a fixed-size chunk buffer. When no buffering argument is
given, the default buffering policy works as follows:
* Binary files are buffered in fixed-size chunks; the size of the buffer
is chosen using a heuristic trying to determine the underlying device's
"block size" and falling back on `io.DEFAULT_BUFFER_SIZE`.
On many systems, the buffer will typically be 4096 or 8192 bytes long.
* "Interactive" text files (files for which isatty() returns True)
use line buffering. Other text files use the policy described above
for binary files.
encoding is the str name of the encoding used to decode or encode the
file. This should only be used in text mode. The default encoding is
platform dependent, but any encoding supported by Python can be
passed. See the codecs module for the list of supported encodings.
errors is an optional string that specifies how encoding errors are to
be handled---this argument should not be used in binary mode. Pass
'strict' to raise a ValueError exception if there is an encoding error
(the default of None has the same effect), or pass 'ignore' to ignore
errors. (Note that ignoring encoding errors can lead to data loss.)
See the documentation for codecs.register for a list of the permitted
encoding error strings.
newline is a string controlling how universal newlines works (it only
applies to text mode). It can be None, '', '\n', '\r', and '\r\n'. It works
as follows:
* On input, if newline is None, universal newlines mode is
enabled. Lines in the input can end in '\n', '\r', or '\r\n', and
these are translated into '\n' before being returned to the
caller. If it is '', universal newline mode is enabled, but line
endings are returned to the caller untranslated. If it has any of
the other legal values, input lines are only terminated by the given
string, and the line ending is returned to the caller untranslated.
* On output, if newline is None, any '\n' characters written are
translated to the system default line separator, os.linesep. If
newline is '', no translation takes place. If newline is any of the
other legal values, any '\n' characters written are translated to
the given string.
closedfd is a bool. If closefd is False, the underlying file descriptor will
be kept open when the file is closed. This does not work when a file name is
given and must be True in that case.
The newly created file is non-inheritable.
A custom opener can be used by passing a callable as *opener*. The
underlying file descriptor for the file object is then obtained by calling
*opener* with (*file*, *flags*). *opener* must return an open file
descriptor (passing os.open as *opener* results in functionality similar to
passing None).
open() returns a file object whose type depends on the mode, and
through which the standard file operations such as reading and writing
are performed. When open() is used to open a file in a text mode ('w',
'r', 'wt', 'rt', etc.), it returns a TextIOWrapper. When used to open
a file in a binary mode, the returned class varies: in read binary
mode, it returns a BufferedReader; in write binary and append binary
modes, it returns a BufferedWriter, and in read/write mode, it returns
a BufferedRandom.
It is also possible to use a string or bytearray as a file for both
reading and writing. For strings StringIO can be used like a file
opened in a text mode, and for bytes a BytesIO can be used like a file
opened in a binary mode.
"""
if not isinstance(file, int):
file = os.fspath(file)
if not isinstance(file, (str, bytes, int)):
raise TypeError("invalid file: %r" % file)
if not isinstance(mode, str):
raise TypeError("invalid mode: %r" % mode)
if not isinstance(buffering, int):
raise TypeError("invalid buffering: %r" % buffering)
if encoding is not None and not isinstance(encoding, str):
raise TypeError("invalid encoding: %r" % encoding)
if errors is not None and not isinstance(errors, str):
raise TypeError("invalid errors: %r" % errors)
modes = set(mode)
if modes - set("axrwb+t") or len(mode) > len(modes):
raise ValueError("invalid mode: %r" % mode)
creating = "x" in modes
reading = "r" in modes
writing = "w" in modes
appending = "a" in modes
updating = "+" in modes
text = "t" in modes
binary = "b" in modes
if text and binary:
raise ValueError("can't have text and binary mode at once")
if creating + reading + writing + appending > 1:
raise ValueError("can't have read/write/append mode at once")
if not (creating or reading or writing or appending):
raise ValueError("must have exactly one of read/write/append mode")
if binary and encoding is not None:
raise ValueError("binary mode doesn't take an encoding argument")
if binary and errors is not None:
raise ValueError("binary mode doesn't take an errors argument")
if binary and newline is not None:
raise ValueError("binary mode doesn't take a newline argument")
if binary and buffering == 1:
import warnings
warnings.warn("line buffering (buffering=1) isn't supported in binary "
"mode, the default buffer size will be used",
RuntimeWarning, 2)
raw = FileIO(file,
(creating and "x" or "") +
(reading and "r" or "") +
(writing and "w" or "") +
(appending and "a" or "") +
(updating and "+" or ""),
closefd, opener=opener)
result = raw
try:
line_buffering = False
if buffering == 1 or buffering < 0 and raw.isatty():
buffering = -1
line_buffering = True
if buffering < 0:
buffering = DEFAULT_BUFFER_SIZE
try:
bs = os.fstat(raw.fileno()).st_blksize
except (OSError, AttributeError):
pass
else:
if bs > 1:
buffering = bs
if buffering < 0:
raise ValueError("invalid buffering size")
if buffering == 0:
if binary:
return result
raise ValueError("can't have unbuffered text I/O")
if updating:
buffer = BufferedRandom(raw, buffering)
elif creating or writing or appending:
buffer = BufferedWriter(raw, buffering)
elif reading:
buffer = BufferedReader(raw, buffering)
else:
raise ValueError("unknown mode: %r" % mode)
result = buffer
if binary:
return result
encoding = text_encoding(encoding)
text = TextIOWrapper(buffer, encoding, errors, newline, line_buffering)
result = text
text.mode = mode
return result
except:
result.close()
raise
# Define a default pure-Python implementation for open_code()
# that does not allow hooks. Warn on first use. Defined for tests.
def _open_code_with_warning(path):
"""Opens the provided file with mode ``'rb'``. This function
should be used when the intent is to treat the contents as
executable code.
``path`` should be an absolute path.
When supported by the runtime, this function can be hooked
in order to allow embedders more control over code files.
This functionality is not supported on the current runtime.
"""
import warnings
warnings.warn("_pyio.open_code() may not be using hooks",
RuntimeWarning, 2)
return open(path, "rb")
try:
open_code = io.open_code
except AttributeError:
open_code = _open_code_with_warning
# In normal operation, both `UnsupportedOperation`s should be bound to the
# same object.
try:
UnsupportedOperation = io.UnsupportedOperation
except AttributeError:
class UnsupportedOperation(OSError, ValueError):
pass
class IOBase(metaclass=abc.ABCMeta):
"""The abstract base class for all I/O classes.
This class provides dummy implementations for many methods that
derived classes can override selectively; the default implementations
represent a file that cannot be read, written or seeked.
Even though IOBase does not declare read or write because
their signatures will vary, implementations and clients should
consider those methods part of the interface. Also, implementations
may raise UnsupportedOperation when operations they do not support are
called.
The basic type used for binary data read from or written to a file is
bytes. Other bytes-like objects are accepted as method arguments too.
Text I/O classes work with str data.
Note that calling any method (even inquiries) on a closed stream is
undefined. Implementations may raise OSError in this case.
IOBase (and its subclasses) support the iterator protocol, meaning
that an IOBase object can be iterated over yielding the lines in a
stream.
IOBase also supports the :keyword:`with` statement. In this example,
fp is closed after the suite of the with statement is complete:
with open('spam.txt', 'r') as fp:
fp.write('Spam and eggs!')
"""
### Internal ###
def _unsupported(self, name):
"""Internal: raise an OSError exception for unsupported operations."""
raise UnsupportedOperation("%s.%s() not supported" %
(self.__class__.__name__, name))
### Positioning ###
def seek(self, pos, whence=0):
"""Change stream position.
Change the stream position to byte offset pos. Argument pos is
interpreted relative to the position indicated by whence. Values
for whence are ints:
* 0 -- start of stream (the default); offset should be zero or positive
* 1 -- current stream position; offset may be negative
* 2 -- end of stream; offset is usually negative
Some operating systems / file systems could provide additional values.
Return an int indicating the new absolute position.
"""
self._unsupported("seek")
def tell(self):
"""Return an int indicating the current stream position."""
return self.seek(0, 1)
def truncate(self, pos=None):
"""Truncate file to size bytes.
Size defaults to the current IO position as reported by tell(). Return
the new size.
"""
self._unsupported("truncate")
### Flush and close ###
def flush(self):
"""Flush write buffers, if applicable.
This is not implemented for read-only and non-blocking streams.
"""
self._checkClosed()
# XXX Should this return the number of bytes written???
__closed = False
def close(self):
"""Flush and close the IO object.
This method has no effect if the file is already closed.
"""
if not self.__closed:
try:
self.flush()
finally:
self.__closed = True
def __del__(self):
"""Destructor. Calls close()."""
try:
closed = self.closed
except AttributeError:
# If getting closed fails, then the object is probably
# in an unusable state, so ignore.
return
if closed:
return
# If close() fails, the caller logs the exception with
# sys.unraisablehook. close() must be called at the end at __del__().
self.close()
### Inquiries ###
def seekable(self):
"""Return a bool indicating whether object supports random access.
If False, seek(), tell() and truncate() will raise OSError.
This method may need to do a test seek().
"""
return False
def _checkSeekable(self, msg=None):
"""Internal: raise UnsupportedOperation if file is not seekable
"""
if not self.seekable():
raise UnsupportedOperation("File or stream is not seekable."
if msg is None else msg)
def readable(self):
"""Return a bool indicating whether object was opened for reading.
If False, read() will raise OSError.
"""
return False
def _checkReadable(self, msg=None):
"""Internal: raise UnsupportedOperation if file is not readable
"""
if not self.readable():
raise UnsupportedOperation("File or stream is not readable."
if msg is None else msg)
def writable(self):
"""Return a bool indicating whether object was opened for writing.
If False, write() and truncate() will raise OSError.
10BC8
"""
return False
def _checkWritable(self, msg=None):
"""Internal: raise UnsupportedOperation if file is not writable
"""
if not self.writable():
raise UnsupportedOperation("File or stream is not writable."
if msg is None else msg)
@property
def closed(self):
"""closed: bool. True iff the file has been closed.
For backwards compatibility, this is a property, not a predicate.
"""
return self.__closed
def _checkClosed(self, msg=None):
"""Internal: raise a ValueError if file is closed
"""
if self.closed:
raise ValueError("I/O operation on closed file."
if msg is None else msg)
### Context manager ###
def __enter__(self): # That's a forward reference
"""Context management protocol. Returns self (an instance of IOBase)."""
self._checkClosed()
return self
def __exit__(self, *args):
"""Context management protocol. Calls close()"""
self.close()
### Lower-level APIs ###
# XXX Should these be present even if unimplemented?
def fileno(self):
"""Returns underlying file descriptor (an int) if one exists.
An OSError is raised if the IO object does not use a file descriptor.
"""
self._unsupported("fileno")
def isatty(self):
"""Return a bool indicating whether this is an 'interactive' stream.
Return False if it can't be determined.
"""
self._checkClosed()
return False
### Readline[s] and writelines ###
def readline(self, size=-1):
r"""Read and return a line of bytes from the stream.
If size is specified, at most size bytes will be read.
Size should be an int.
The line terminator is always b'\n' for binary files; for text
files, the newlines argument to open can be used to select the line
terminator(s) recognized.
"""
# For backwards compatibility, a (slowish) readline().
if hasattr(self, "peek"):
def nreadahead():
readahead = self.peek(1)
if not readahead:
return 1
n = (readahead.find(b"\n") + 1) or len(readahead)
if size >= 0:
n = min(n, size)
return n
else:
def nreadahead():
return 1
if size is None:
size = -1
else:
try:
size_index = size.__index__
except AttributeError:
raise TypeError(f"{size!r} is not an integer")
else:
size = size_index()
res = bytearray()
while size < 0 or len(res) < size:
b = self.read(nreadahead())
if not b:
break
res += b
if res.endswith(b"\n"):
break
return bytes(res)
def __iter__(self):
self._checkClosed()
return self
def __next__(self):
line = self.readline()
if not line:
raise StopIteration
return line
def readlines(self, hint=None):
"""Return a list of lines from the stream.
hint can be specified to control the number of lines read: no more
lines will be read if the total size (in bytes/characters) of all
lines so far exceeds hint.
"""
if hint is None or hint <= 0:
return list(self)
n = 0
lines = []
for line in self:
lines.append(line)
n += len(line)
if n >= hint:
break
return lines
def writelines(self, lines):
"""Write a list of lines to the stream.
Line separators are not added, so it is usual for each of the lines
provided to have a line separator at the end.
"""
self._checkClosed()
for line in lines:
self.write(line)
io.IOBase.register(IOBase)
class RawIOBase(IOBase):
"""Base class for raw binary I/O."""
# The read() method is implemented by calling readinto(); derived
# classes that want to support read() only need to implement
# readinto() as a primitive operation. In general, readinto() can be
# more efficient than read().
# (It would be tempting to also provide an implementation of
# readinto() in terms of read(), in case the latter is a more suitable
# primitive operation, but that would lead to nasty recursion in case
# a subclass doesn't implement either.)
def read(self, size=-1):
"""Read and return up to size bytes, where size is an int.
Returns an empty bytes object on EOF, or None if the object is
set not to block and has no data to read.
"""
if size is None:
size = -1
if size < 0:
return self.readall()
b = bytearray(size.__index__())
n = self.readinto(b)
if n is None:
return None
del b[n:]
return bytes(b)
def readall(self):
"""Read until EOF, using multiple read() call."""
res = bytearray()
while data := self.read(DEFAULT_BUFFER_SIZE):
res += data
if res:
return bytes(res)
else:
# b'' or None
return data
def readinto(self, b):
"""Read bytes into a pre-allocated bytes-like object b.
Returns an int representing the number of bytes read (0 for EOF), or
None if the object is set not to block and has no data to read.
"""
self._unsupported("readinto")
def write(self, b):
"""Write the given buffer to the IO stream.
Returns the number of bytes written, which may be less than the
length of b in bytes.
"""
self._unsupported("write")
io.RawIOBase.register(RawIOBase)
from _io import FileIO
RawIOBase.register(FileIO)
class BufferedIOBase(IOBase):
"""Base class for buffered IO objects.
The main difference with RawIOBase is that the read() method
supports omitting the size argument, and does not have a default
implementation that defers to readinto().
In addition, read(), readinto() and write() may raise
BlockingIOError if the underlying raw stream is in non-blocking
mode and not ready; unlike their raw counterparts, they will never
return None.
A typical implementation should not inherit from a RawIOBase
implementation, but wrap one.
"""
def read(self, size=-1):
"""Read and return up to size bytes, where size is an int.
If the argument is omitted, None, or negative, reads and
returns all data until EOF.
If the argument is positive, and the underlying raw stream is
not 'interactive', multiple raw reads may be issued to satisfy
the byte count (unless EOF is reached first). But for
interactive raw streams (XXX and for pipes?), at most one raw
read will be issued, and a short result does not imply that
EOF is imminent.
Returns an empty bytes array on EOF.
Raises BlockingIOError if the underlying raw stream has no
data at the moment.
"""
self._unsupported("read")
def read1(self, size=-1):
"""Read up to size bytes with at most one read() system call,
where size is an int.
"""
self._unsupported("read1")
def readinto(self, b):
"""Read bytes into a pre-allocated bytes-like object b.
Like read(), this may issue multiple reads to the underlying raw
stream, unless the latter is 'interactive'.
Returns an int representing the number of bytes read (0 for EOF).
Raises BlockingIOError if the underlying raw stream has no
data at the moment.
"""
return self._readinto(b, read1=False)
def readinto1(self, b):
"""Read bytes into buffer *b*, using at most one system call
Returns an int representing the number of bytes read (0 for EOF).
Raises BlockingIOError if the underlying raw stream has no
data at the moment.
"""
return self._readinto(b, read1=True)
def _readinto(self, b, read1):
if not isinstance(b, memoryview):
b = memoryview(b)
b = b.cast('B')
if read1:
data = self.read1(len(b))
else:
data = self.read(len(b))
n = len(data)
b[:n] = data
return n
def write(self, b):
"""Write the given bytes buffer to the IO stream.
Return the number of bytes written, which is always the length of b
in bytes.
Raises BlockingIOError if the buffer is full and the
underlying raw stream cannot accept more data at the moment.
"""
self._unsupported("write")
def detach(self):
"""
Separate the underlying raw stream from the buffer and return it.
After the raw stream has been detached, the buffer is in an unusable
state.
"""
self._unsupported("detach")
io.BufferedIOBase.register(BufferedIOBase)
class _BufferedIOMixin(BufferedIOBase):
"""A mixin implementation of BufferedIOBase with an underlying raw stream.
This passes most requests on to the underlying raw stream. It
does *not* provide implementations of read(), readinto() or
write().
"""
def __init__(self, raw):
self._raw = raw
### Positioning ###
def seek(self, pos, whence=0):
new_position = self.raw.seek(pos, whence)
if new_position < 0:
raise OSError("seek() returned an invalid position")
return new_position
def tell(self):
pos = self.raw.tell()
if pos < 0:
raise OSError("tell() returned an invalid position")
return pos
def truncate(self, pos=None):
self._checkClosed()
self._checkWritable()
# Flush the stream. We're mixing buffered I/O with lower-level I/O,
# and a flush may be necessary to synch both views of the current
# file state.
self.flush()
if pos is None:
pos = self.tell()
# XXX: Should seek() be used, instead of passing the position
# XXX directly to truncate?
return self.raw.truncate(pos)
### Flush and close ###
def flush(self):
if self.closed:
raise ValueError("flush on closed file")
self.raw.flush()
def close(self):
if self.raw is not None and not self.closed:
try:
# may raise BlockingIOError or BrokenPipeError etc
self.flush()
finally:
self.raw.close()
def detach(self):
if self.raw is None:
raise ValueError("raw stream already detached")
self.flush()
raw = self._raw
self._raw = None
return raw
### Inquiries ###
def seekable(self):
return self.raw.seekable()
@property
def raw(self):
return self._raw
@property
def closed(self):
return self.raw.closed
@property
def name(self):
return self.raw.name
@property
def mode(self):
return self.raw.mode
def __getstate__(self):
raise TypeError(f"cannot pickle {self.__class__.__name__!r} object")
def __repr__(self):
modname = self.__class__.__module__
clsname = self.__class__.__qualname__
try:
name = self.name
except AttributeError:
return "<{}.{}>".format(modname, clsname)
else:
return "<{}.{} name={!r}>".format(modname, clsname, name)
### Lower-level APIs ###
def fileno(self):
return self.raw.fileno()
def isatty(self):
return self.raw.isatty()
class BytesIO(BufferedIOBase):
"""Buffered I/O implementation using an in-memory bytes buffer."""
# Initialize _buffer as soon as possible since it's used by __del__()
# which calls close()
_buffer = None
def __init__(self, initial_bytes=None):
buf = bytearray()
if initial_bytes is not None:
buf += initial_bytes
self._buffer = buf
self._pos = 0
def __getstate__(self):
if self.closed:
raise ValueError("__getstate__ on closed file")
return self.__dict__.copy()
def getvalue(self):
"""Return the bytes value (contents) of the buffer
"""
if self.closed:
raise ValueError("getvalue on closed file")
return bytes(self._buffer)
def getbuffer(self):
"""Return a readable and writable view of the buffer.
"""
if self.closed:
raise ValueError("getbuffer on closed file")
return memoryview(self._buffer)
def close(self):
if self._buffer is not None:
self._buffer.clear()
super().close()
def read(self, size=-1):
if self.closed:
raise ValueError("read from closed file")
if size is None:
size = -1
else:
try:
size_index = size.__index__
except AttributeError:
raise TypeError(f"{size!r} is not an integer")
else:
size = size_index()
if size < 0:
size = len(self._buffer)
if len(self._buffer) <= self._pos:
return b""
newpos = min(len(self._buffer), self._pos + size)
b = self._buffer[self._pos : newpos]
self._pos = newpos
return bytes(b)
def read1(self, size=-1):
"""This is the same as read.
"""
return self.read(size)
def write(self, b):
if self.closed:
raise ValueError("write to closed file")
if isinstance(b, str):
raise TypeError("can't write str to binary stream")
with memoryview(b) as view:
n = view.nbytes # Size of any bytes-like object
if n == 0:
return 0
pos = self._pos
if pos > len(self._buffer):
# Inserts null bytes between the current end of the file
# and the new write position.
padding = b'\x00' * (pos - len(self._buffer))
self._buffer += padding
self._buffer[pos:pos + n] = b
self._pos += n
return n
def seek(self, pos, whence=0):
if self.closed:
raise ValueError("seek on closed file")
try:
pos_index = pos.__index__
except AttributeError:
raise TypeError(f"{pos!r} is not an integer")
else:
pos = pos_index()
if whence == 0:
if pos < 0:
raise ValueError("negative seek position %r" % (pos,))
self._pos = pos
elif whence == 1:
self._pos = max(0, self._pos + pos)
elif whence == 2:
self._pos = max(0, len(self._buffer) + pos)
else:
raise ValueError("unsupported whence value")
return self._pos
def tell(self):
if self.closed:
raise ValueError("tell on closed file")
return self._pos
def truncate(self, pos=None):
if self.closed:
raise ValueError("truncate on closed file")
if pos is None:
pos = self._pos
else:
try:
pos_index = pos.__index__
except AttributeError:
raise TypeError(f"{pos!r} is not an integer")
else:
pos = pos_index()
if pos < 0:
raise ValueError("negative truncate position %r" % (pos,))
del self._buffer[pos:]
return pos
def readable(self):
if self.closed:
raise ValueError("I/O operation on closed file.")