Python implementation of the io module.
# 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
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 io.IOBase finalizer log the exception if the close() method fails?
# The exception is ignored silently by default in release build.
_IOBASE_EMITS_UNRAISABLE = (hasattr(sys, "gettotalrefcount") or sys.flags.dev_mode)
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
========= ===============================================================
--------- ---------------------------------------------------------------
'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
'+' open a disk file for updating (reading and writing)
'U' universal newline mode (deprecated)
========= ===============================================================
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.
'U' mode is deprecated and will raise an exception in future versions
of Python. It has no effect in Python 3. Use newline to control
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
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
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
* 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
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
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
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
if not isinstance(file, int):
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)
if modes - set("axrwb+tU") or len(mode) > len(modes):
raise ValueError("invalid mode: %r" % mode)
if creating or writing or appending or updating:
raise ValueError("mode U cannot be combined with 'x', 'w', 'a', or '+'")
warnings.warn("'U' mode is deprecated",
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:
warnings.warn("line buffering (buffering=1) isn't supported in binary "
"mode, the default buffer size will be used",
(creating and "x" or "") +
(reading and "r" or "") +
(writing and "w" or "") +
(appending and "a" or "") +
(updating and "+" or ""),
if buffering == 1 or buffering < 0 and raw.isatty():
buffering = DEFAULT_BUFFER_SIZE
bs = os.fstat(raw.fileno()).st_blksize
except (OSError, AttributeError):
raise ValueError("invalid buffering size")
raise ValueError("can't have unbuffered text I/O")
buffer = BufferedRandom(raw, buffering)
elif creating or writing or appending:
buffer = BufferedWriter(raw, buffering)
buffer = BufferedReader(raw, buffering)
raise ValueError("unknown mode: %r" % mode)
text = TextIOWrapper(buffer, encoding, errors, newline, line_buffering)
# 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
``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.
warnings.warn("_pyio.open_code() may not be using hooks",
open_code = _open_code_with_warning
"""Helper for builtins.open.__doc__
def __get__(self, obj, typ=None):
"open(file, mode='r', buffering=-1, encoding=None, "
"errors=None, newline=None, closefd=True)\n\n" +
"""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 initstdio() in Python/pylifecycle.c.
__doc__ = DocDescriptor()
def __new__(cls, *args, **kwargs):
return open(*args, **kwargs)
# In normal operation, both `UnsupportedOperation`s should be bound to the
UnsupportedOperation = io.UnsupportedOperation
class UnsupportedOperation(OSError, ValueError):
class IOBase(metaclass=abc.ABCMeta):
"""The abstract base class for all I/O classes, acting on streams of
bytes. There is no public constructor.
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
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
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!')
def _unsupported(self, name):
"""Internal: raise an OSError exception for unsupported operations."""
raise UnsupportedOperation("%s.%s() not supported" %
(self.__class__.__name__, name))
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
* 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")
"""Return an int indicating the current stream position."""
def truncate(self, pos=None):
"""Truncate file to size bytes.
Size defaults to the current IO position as reported by tell(). Return
self._unsupported("truncate")
"""Flush write buffers, if applicable.
This is not implemented for read-only and non-blocking streams.
# XXX Should this return the number of bytes written???
"""Flush and close the IO object.
This method has no effect if the file is already closed.
"""Destructor. Calls close()."""
# If getting closed fails, then the object is probably
# in an unusable state, so ignore.
if _IOBASE_EMITS_UNRAISABLE:
# The try/except block is in case this is called at program
# exit time, when it's possible that globals have already been
# deleted, and then the close() call might fail. Since
# there's nothing we can do about such failures and they annoy
# the end users, we suppress the traceback.
"""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().
def _checkSeekable(self, msg=None):
"""Internal: raise UnsupportedOperation if file is not seekable
raise UnsupportedOperation("File or stream is not seekable."
"""Return a bool indicating whether object was opened for reading.
If False, read() will raise OSError.
def _checkReadable(self, msg=None):
"""Internal: raise UnsupportedOperation if file is not readable
raise UnsupportedOperation("File or stream is not readable."
"""Return a bool indicating whether object was opened for writing.
If False, write() and truncate() will raise OSError.
def _checkWritable(self, msg=None):
"""Internal: raise UnsupportedOperation if file is not writable
raise UnsupportedOperation("File or stream is not writable."
"""closed: bool. True iff the file has been closed.
For backwards compatibility, this is a property, not a predicate.
def _checkClosed(self, msg=None):
"""Internal: raise a ValueError if file is closed
raise ValueError("I/O operation on closed file."
def __enter__(self): # That's a forward reference
"""Context management protocol. Returns self (an instance of IOBase)."""
def __exit__(self, *args):
"""Context management protocol. Calls close()"""
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