Python os.read() Examples

def read_from_fd(self):
        try:
            chunk = os.read(self.fd, self.read_chunk_size)
        except (IOError, OSError) as e:
            if errno_from_exception(e) in _ERRNO_WOULDBLOCK:
                return None
            elif errno_from_exception(e) == errno.EBADF:
                # If the writing half of a pipe is closed, select will
                # report it as readable but reads will fail with EBADF.
                self.close(exc_info=True)
                return None
            else:
                raise
        if not chunk:
            self.close()
            return None
        return chunk 

def read(self, size=None):
        """Return the next size number of bytes from the stream.
           If size is not defined, return all bytes of the stream
           up to EOF.
        """
        if size is None:
            t = []
            while True:
                buf = self._read(self.bufsize)
                if not buf:
                    break
                t.append(buf)
            buf = "".join(t)
        else:
            buf = self._read(size)
        self.pos += len(buf)
        return buf 

def test_dupfile(tmpfile):
    flist = []
    for i in range(5):
        nf = py.io.dupfile(tmpfile, encoding="utf-8")
        assert nf != tmpfile
        assert nf.fileno() != tmpfile.fileno()
        assert nf not in flist
        print_(i, end="", file=nf)
        flist.append(nf)
    for i in range(5):
        f = flist[i]
        f.close()
    tmpfile.seek(0)
    s = tmpfile.read()
    assert "01234" in repr(s)
    tmpfile.close() 

def copyfileobj(src, dst, length=None):
    """Copy length bytes from fileobj src to fileobj dst.
       If length is None, copy the entire content.
    """
    if length == 0:
        return
    if length is None:
        shutil.copyfileobj(src, dst)
        return

    BUFSIZE = 16 * 1024
    blocks, remainder = divmod(length, BUFSIZE)
    for b in range(blocks):
        buf = src.read(BUFSIZE)
        if len(buf) < BUFSIZE:
            raise IOError("end of file reached")
        dst.write(buf)

    if remainder != 0:
        buf = src.read(remainder)
        if len(buf) < remainder:
            raise IOError("end of file reached")
        dst.write(buf)
    return 

def addfile(self, tarinfo, fileobj=None):
        """Add the TarInfo object `tarinfo' to the archive. If `fileobj' is
           given, tarinfo.size bytes are read from it and added to the archive.
           You can create TarInfo objects using gettarinfo().
           On Windows platforms, `fileobj' should always be opened with mode
           'rb' to avoid irritation about the file size.
        """
        self._check("aw")

        tarinfo = copy.copy(tarinfo)

        buf = tarinfo.tobuf(self.format, self.encoding, self.errors)
        self.fileobj.write(buf)
        self.offset += len(buf)

        # If there's data to follow, append it.
        if fileobj is not None:
            copyfileobj(fileobj, self.fileobj, tarinfo.size)
            blocks, remainder = divmod(tarinfo.size, BLOCKSIZE)
            if remainder > 0:
                self.fileobj.write(NUL * (BLOCKSIZE - remainder))
                blocks += 1
            self.offset += blocks * BLOCKSIZE

        self.members.append(tarinfo) 

def handle_signal_wakeup(self):
        """Handle a newly arrived signal.

        This gets called via self._notifier when there's a signal.

        Python will get control here, so the signal will get handled.
        """
        assert self._notifier is not None
        log.destroy.debug("Handling signal wakeup!")
        self._notifier.setEnabled(False)
        read_fd = self._notifier.socket()
        try:
            os.read(int(read_fd), 1)
        except OSError:
            log.destroy.exception("Failed to read wakeup fd.")
        self._notifier.setEnabled(True) 

def init_faulthandler(self):
        """Handle a segfault from a previous run and set up faulthandler."""
        logname = os.path.join(standarddir.data(), 'crash.log')
        try:
            # First check if an old logfile exists.
            if os.path.exists(logname):
                with open(logname, 'r', encoding='ascii') as f:
                    self._crash_log_data = f.read()
                os.remove(logname)
                self._init_crashlogfile()
            else:
                # There's no log file, so we can use this to display crashes to
                # the user on the next start.
                self._init_crashlogfile()
        except OSError:
            log.init.exception("Error while handling crash log file!")
            self._init_crashlogfile() 

def _get(self):
        if not self._getMode:
            return
        buf = os.read(self._rt, _MAXLINE).decode()
        if not buf:
            raise CosimulationError(_error.SimulationEnd)
        e = buf.split()
        for i in range(1, len(e), 2):
            s, v = self._toSigDict[e[i]], e[i + 1]
            if v in 'zZ':
                next = None
            elif v in 'xX':
                next = s._init
            else:
                try:
                    next = int(v, 16)
                    if s._nrbits and s._min is not None and s._min < 0:
                        if next >= (1 << (s._nrbits - 1)):
                            next |= (-1 << s._nrbits)
                except ValueError:
                    next = intbv(0)
            s.next = next

        self._getMode = 0 

def read_from_fd(self):
        try:
            chunk = os.read(self.fd, self.read_chunk_size)
        except (IOError, OSError) as e:
            if errno_from_exception(e) in _ERRNO_WOULDBLOCK:
                return None
            elif errno_from_exception(e) == errno.EBADF:
                # If the writing half of a pipe is closed, select will
                # report it as readable but reads will fail with EBADF.
                self.close(exc_info=True)
                return None
            else:
                raise
        if not chunk:
            self.close()
            return None
        return chunk 

def __next__(self):
        """Return the next item using TarFile's next() method.
           When all members have been read, set TarFile as _loaded.
        """
        # Fix for SF #1100429: Under rare circumstances it can
        # happen that getmembers() is called during iteration,
        # which will cause TarIter to stop prematurely.

        if self.index == 0 and self.tarfile.firstmember is not None:
            tarinfo = self.tarfile.next()
        elif self.index < len(self.tarfile.members):
            tarinfo = self.tarfile.members[self.index]
        elif not self.tarfile._loaded:
            tarinfo = self.tarfile.next()
            if not tarinfo:
                self.tarfile._loaded = True
                raise StopIteration
        else:
            raise StopIteration
        self.index += 1
        return tarinfo

#--------------------
# exported functions
#-------------------- 

def fromtarfile(cls, tarfile):
        """Return the next TarInfo object from TarFile object
           tarfile.
        """
        buf = tarfile.fileobj.read(BLOCKSIZE)
        obj = cls.frombuf(buf, tarfile.encoding, tarfile.errors)
        obj.offset = tarfile.fileobj.tell() - BLOCKSIZE
        return obj._proc_member(tarfile)

    #--------------------------------------------------------------------------
    # The following are methods that are called depending on the type of a
    # member. The entry point is _proc_member() which can be overridden in a
    # subclass to add custom _proc_*() methods. A _proc_*() method MUST
    # implement the following
    # operations:
    # 1. Set self.offset_data to the position where the data blocks begin,
    #    if there is data that follows.
    # 2. Set tarfile.offset to the position where the next member's header will
    #    begin.
    # 3. Return self or another valid TarInfo object. 

def receive_output(self, max_read_size, timeout=0):
        """
        Poll the shell output
        """
        (ready, _, _) = select.select([self._master_fd], [], [], timeout)
        if not ready:
            return None

        try:
            data = os.read(self._master_fd, max_read_size)
        except OSError:
            return None

        return data 

def _handle_read(self):
        try:
            pos = self._read_to_buffer_loop()
        except UnsatisfiableReadError:
            raise
        except Exception as e:
            gen_log.warning("error on read: %s" % e)
            self.close(exc_info=True)
            return
        if pos is not None:
            self._read_from_buffer(pos)
            return
        else:
            self._maybe_run_close_callback() 

def _try_inline_read(self):
        """Attempt to complete the current read operation from buffered data.

        If the read can be completed without blocking, schedules the
        read callback on the next IOLoop iteration; otherwise starts
        listening for reads on the socket.
        """
        # See if we've already got the data from a previous read
        self._run_streaming_callback()
        pos = self._find_read_pos()
        if pos is not None:
            self._read_from_buffer(pos)
            return
        self._check_closed()
        try:
            pos = self._read_to_buffer_loop()
        except Exception:
            # If there was an in _read_to_buffer, we called close() already,
            # but couldn't run the close callback because of _pending_callbacks.
            # Before we escape from this function, run the close callback if
            # applicable.
            self._maybe_run_close_callback()
            raise
        if pos is not None:
            self._read_from_buffer(pos)
            return
        # We couldn't satisfy the read inline, so either close the stream
        # or listen for new data.
        if self.closed():
            self._maybe_run_close_callback()
        else:
            self._add_io_state(ioloop.IOLoop.READ) 

def copyfileobj(src, dst, length=None):
    """Copy length bytes from fileobj src to fileobj dst.
       If length is None, copy the entire content.
    """
    if length == 0:
        return
    if length is None:
        while True:
            buf = src.read(16*1024)
            if not buf:
                break
            dst.write(buf)
        return

    BUFSIZE = 16 * 1024
    blocks, remainder = divmod(length, BUFSIZE)
    for b in range(blocks):
        buf = src.read(BUFSIZE)
        if len(buf) < BUFSIZE:
            raise IOError("end of file reached")
        dst.write(buf)

    if remainder != 0:
        buf = src.read(remainder)
        if len(buf) < remainder:
            raise IOError("end of file reached")
        dst.write(buf)
    return 

def test_stdin_nulled_by_default(self):
        print ("XXX this test may well hang instead of crashing")
        print ("XXX which indicates an error in the underlying capturing")
        print ("XXX mechanisms")
        cap = self.getcapture()
        py.test.raises(IOError, "sys.stdin.read()")
        out, err = cap.reset() 

def compute(self) -> None:
        """If active, read output from the cava program.
        Make sure that the most recent frame is always fully available,
        Stores incomplete frames for the next update."""
        # do not compute if no program uses cava
        if self.consumers == 0:
            return
        # read the fifo until we get to the current frame
        while True:
            try:
                read = os.read(
                    self.cava_fifo, self.frame_length - len(self.growing_frame)
                )
                if read == b"":
                    return
                self.growing_frame += read
            except OSError as e:
                if e.errno == errno.EAGAIN or e.errno == errno.EWOULDBLOCK:
                    # there were not enough bytes for a whole frame, keep the old frame
                    return

            # we read a whole frame, update the factors
            if len(self.growing_frame) == self.frame_length:
                # vol = max(0.01, self.lights.base.musiq.player.volume)
                # self.current_frame = [int(b) / 255 / vol for b in self.growing_frame]
                self.current_frame = [int(b) / 255 for b in self.growing_frame]
                self.growing_frame = b"" 

def exec_cc(cmd, args):
    """
    Execute with current context.
    Yes, you're right -- I'm naming it after call/cc.

    Return a generator.
        The first yielded one is the status of
        the execution of subprocess command.

        The following ones are the the buffer batches of stderr,
        each of which is a Python 'bytes' object
    """
    file = cmd
    err_in, err_out = os.pipe()
    out_in, out_out = os.pipe()
    if os.fork():
        _, status = os.wait()
        os.close(err_out)
        os.close(out_out)
        yield status
        while True:
            load = os.read(err_in, 1024)
            if not load:
                break
            yield load
    else:
        # for child process
        os.close(err_in)
        os.close(out_in)
        os.dup2(err_out, sys.stderr.fileno())
        os.dup2(out_out, sys.stdout.fileno())

        os.execvpe(file, [cmd, *args], dict(os.environ))
        # in case that os.execvp fails
        sys.exit(127) 

def print_(self):
        if isinstance(self.stdin, TextIOWrapper):
            s = self.stdin.read()
            print(s, end='' if s.endswith('\n') else '\n', file=self.outfp)
        elif isinstance(self.stdin, str):
            print(self.stdin, end='' if self.stdin.endswith('\n') else '\n',
                  file=self.outfp)
        elif self.lastResultIsList:
            print('\n'.join(self.stdin), file=self.outfp)
        else:
            print(self.stdin, file=self.outfp) 

def _handle_read(self):
        try:
            pos = self._read_to_buffer_loop()
        except UnsatisfiableReadError:
            raise
        except Exception as e:
            gen_log.warning("error on read: %s" % e)
            self.close(exc_info=True)
            return
        if pos is not None:
            self._read_from_buffer(pos)
            return
        else:
            self._maybe_run_close_callback() 

def read_until_close(self, callback=None, streaming_callback=None):
        """Asynchronously reads all data from the socket until it is closed.

        If a ``streaming_callback`` is given, it will be called with chunks
        of data as they become available, and the final result will be empty.
        Otherwise, the result is all the data that was read.
        If a callback is given, it will be run with the data as an argument;
        if not, this method returns a `.Future`.

        Note that if a ``streaming_callback`` is used, data will be
        read from the socket as quickly as it becomes available; there
        is no way to apply backpressure or cancel the reads. If flow
        control or cancellation are desired, use a loop with
        `read_bytes(partial=True) <.read_bytes>` instead.

        .. versionchanged:: 4.0
            The callback argument is now optional and a `.Future` will
            be returned if it is omitted.

        """
        future = self._set_read_callback(callback)
        self._streaming_callback = stack_context.wrap(streaming_callback)
        if self.closed():
            if self._streaming_callback is not None:
                self._run_read_callback(self._read_buffer_size, True)
            self._run_read_callback(self._read_buffer_size, False)
            return future
        self._read_until_close = True
        try:
            self._try_inline_read()
        except:
            if future is not None:
                future.add_done_callback(lambda f: f.exception())
            raise
        return future 

def read_bytes(self, num_bytes, callback=None, streaming_callback=None,
                   partial=False):
        """Asynchronously read a number of bytes.

        If a ``streaming_callback`` is given, it will be called with chunks
        of data as they become available, and the final result will be empty.
        Otherwise, the result is all the data that was read.
        If a callback is given, it will be run with the data as an argument;
        if not, this method returns a `.Future`.

        If ``partial`` is true, the callback is run as soon as we have
        any bytes to return (but never more than ``num_bytes``)

        .. versionchanged:: 4.0
            Added the ``partial`` argument.  The callback argument is now
            optional and a `.Future` will be returned if it is omitted.
        """
        future = self._set_read_callback(callback)
        assert isinstance(num_bytes, numbers.Integral)
        self._read_bytes = num_bytes
        self._read_partial = partial
        self._streaming_callback = stack_context.wrap(streaming_callback)
        try:
            self._try_inline_read()
        except:
            if future is not None:
                future.add_done_callback(lambda f: f.exception())
            raise
        return future 

def read_until(self, delimiter, callback=None, max_bytes=None):
        """Asynchronously read until we have found the given delimiter.

        The result includes all the data read including the delimiter.
        If a callback is given, it will be run with the data as an argument;
        if not, this method returns a `.Future`.

        If ``max_bytes`` is not None, the connection will be closed
        if more than ``max_bytes`` bytes have been read and the delimiter
        is not found.

        .. versionchanged:: 4.0
            Added the ``max_bytes`` argument.  The ``callback`` argument is
            now optional and a `.Future` will be returned if it is omitted.
        """
        future = self._set_read_callback(callback)
        self._read_delimiter = delimiter
        self._read_max_bytes = max_bytes
        try:
            self._try_inline_read()
        except UnsatisfiableReadError as e:
            # Handle this the same way as in _handle_events.
            gen_log.info("Unsatisfiable read, closing connection: %s" % e)
            self.close(exc_info=True)
            return future
        except:
            if future is not None:
                future.add_done_callback(lambda f: f.exception())
            raise
        return future 

def read_until_regex(self, regex, callback=None, max_bytes=None):
        """Asynchronously read until we have matched the given regex.

        The result includes the data that matches the regex and anything
        that came before it.  If a callback is given, it will be run
        with the data as an argument; if not, this method returns a
        `.Future`.

        If ``max_bytes`` is not None, the connection will be closed
        if more than ``max_bytes`` bytes have been read and the regex is
        not satisfied.

        .. versionchanged:: 4.0
            Added the ``max_bytes`` argument.  The ``callback`` argument is
            now optional and a `.Future` will be returned if it is omitted.
        """
        future = self._set_read_callback(callback)
        self._read_regex = re.compile(regex)
        self._read_max_bytes = max_bytes
        try:
            self._try_inline_read()
        except UnsatisfiableReadError as e:
            # Handle this the same way as in _handle_events.
            gen_log.info("Unsatisfiable read, closing connection: %s" % e)
            self.close(exc_info=True)
            return future
        except:
            if future is not None:
                # Ensure that the future doesn't log an error because its
                # failure was never examined.
                future.add_done_callback(lambda f: f.exception())
            raise
        return future 

def read_from_fd(self):
        """Attempts to read from the underlying file.

        Returns ``None`` if there was nothing to read (the socket
        returned `~errno.EWOULDBLOCK` or equivalent), otherwise
        returns the data.  When possible, should return no more than
        ``self.read_chunk_size`` bytes at a time.
        """
        raise NotImplementedError() 

def read_from_fd(self):
        if self._ssl_accepting:
            # If the handshake hasn't finished yet, there can't be anything
            # to read (attempting to read may or may not raise an exception
            # depending on the SSL version)
            return None
        try:
            # SSLSocket objects have both a read() and recv() method,
            # while regular sockets only have recv().
            # The recv() method blocks (at least in python 2.6) if it is
            # called when there is nothing to read, so we have to use
            # read() instead.
            chunk = self.socket.read(self.read_chunk_size)
        except ssl.SSLError as e:
            # SSLError is a subclass of socket.error, so this except
            # block must come first.
            if e.args[0] == ssl.SSL_ERROR_WANT_READ:
                return None
            else:
                raise
        except socket.error as e:
            if e.args[0] in _ERRNO_WOULDBLOCK:
                return None
            else:
                raise
        if not chunk:
            self.close()
            return None
        return chunk 

def _maybe_add_error_listener(self):
        # This method is part of an optimization: to detect a connection that
        # is closed when we're not actively reading or writing, we must listen
        # for read events.  However, it is inefficient to do this when the
        # connection is first established because we are going to read or write
        # immediately anyway.  Instead, we insert checks at various times to
        # see if the connection is idle and add the read listener then.
        if self._pending_callbacks != 0:
            return
        if self._state is None or self._state == ioloop.IOLoop.ERROR:
            if self.closed():
                self._maybe_run_close_callback()
            elif (self._read_buffer_size == 0 and
                  self._close_callback is not None):
                self._add_io_state(ioloop.IOLoop.READ) 

def _read_from_buffer(self, pos):
        """Attempts to complete the currently-pending read from the buffer.

        The argument is either a position in the read buffer or None,
        as returned by _find_read_pos.
        """
        self._read_bytes = self._read_delimiter = self._read_regex = None
        self._read_partial = False
        self._run_read_callback(pos, False) 

def _try_inline_read(self):
        """Attempt to complete the current read operation from buffered data.

        If the read can be completed without blocking, schedules the
        read callback on the next IOLoop iteration; otherwise starts
        listening for reads on the socket.
        """
        # See if we've already got the data from a previous read
        self._run_streaming_callback()
        pos = self._find_read_pos()
        if pos is not None:
            self._read_from_buffer(pos)
            return
        self._check_closed()
        try:
            pos = self._read_to_buffer_loop()
        except Exception:
            # If there was an in _read_to_buffer, we called close() already,
            # but couldn't run the close callback because of _pending_callbacks.
            # Before we escape from this function, run the close callback if
            # applicable.
            self._maybe_run_close_callback()
            raise
        if pos is not None:
            self._read_from_buffer(pos)
            return
        # We couldn't satisfy the read inline, so either close the stream
        # or listen for new data.
        if self.closed():
            self._maybe_run_close_callback()
        else:
            self._add_io_state(ioloop.IOLoop.READ) 

def _maybe_run_close_callback(self):
        # If there are pending callbacks, don't run the close callback
        # until they're done (see _maybe_add_error_handler)
        if self.closed() and self._pending_callbacks == 0:
            futures = []
            if self._read_future is not None:
                futures.append(self._read_future)
                self._read_future = None
            if self._write_future is not None:
                futures.append(self._write_future)
                self._write_future = None
            if self._connect_future is not None:
                futures.append(self._connect_future)
                self._connect_future = None
            if self._ssl_connect_future is not None:
                futures.append(self._ssl_connect_future)
                self._ssl_connect_future = None
            for future in futures:
                future.set_exception(StreamClosedError(real_error=self.error))
            if self._close_callback is not None:
                cb = self._close_callback
                self._close_callback = None
                self._run_callback(cb)
            # Delete any unfinished callbacks to break up reference cycles.
            self._read_callback = self._write_callback = None
            # Clear the buffers so they can be cleared immediately even
            # if the IOStream object is kept alive by a reference cycle.
            # TODO: Clear the read buffer too; it currently breaks some tests.
            self._write_buffer = None