#!/usr/bin/python3

r"""
Split up a file and yield its pieces based on some line terminator.

Usage looks like:
    $ /usr/local/cpython-3.6/bin/python3
    Python 3.6.0 (default, Apr 22 2017, 09:17:19)
    [GCC 5.4.0 20160609] on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import readline0
    >>> file_ = open('/etc/shells', 'r')
    >>> for line in readline0.readline0(file_=file_, separator=b'\n'):
    ...     print(line)
    ...
    b'# /etc/shells: valid login shells'
    b'/bin/sh'
    b'/bin/dash'
    b'/bin/bash'
    b'/bin/rbash'
    >>>

Of course separator need not be a newline; it defaults to a null byte.
"""

# This software is the proprietary property of The Regents of the University of California ("The Regents") Copyright (c)
# 1993-2006 The Regents of the University of California, Irvine campus. All Rights Reserved.

# Redistributions of source code must retain the above copyright notice, this list of conditions and the following
# disclaimer.

# Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following
# disclaimer in the documentation and/or other materials provided with the distribution.

# Neither the name of The Regents nor the names of its contributors may be used to endorse or promote products derived
# from this software without specific prior written permission.

# The end-user understands that the program was developed for research purposes and is advised not to rely exclusively
# on the program for any reason.

# THE SOFTWARE PROVIDED IS ON AN "AS IS" BASIS, AND THE REGENTS AND CONTRIBUTORS HAVE NO OBLIGATION TO PROVIDE
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import io
import os
import sys
import typing
import collections.abc


def readline0(
    file_: typing.Union[typing.BinaryIO, int] = sys.stdin.buffer, separator: bytes = b"\0", blocksize: int = 2**16
) -> collections.abc.Iterator[bytes]:
    """
    Instantiate Readline0 class and yield what we get back.

    file_ defaults to sys.stdin, separator defaults to a null, and blocksize defaults to 64K.
    """
    readline0_obj = Readline0(file_, separator, blocksize)
    # FIXME: This should become a yield from eventually.
    for line in readline0_obj.sequence():
        yield line


class Readline0:
    """Yield a series of blocks, separated by separator."""

    # This class assumes that there will be a null once in a while.  If you feed it with a huge block of data that has
    # no nulls (line separators), woe betide you.
    def __init__(self, file_: typing.Union[typing.BinaryIO, int], separator: bytes, blocksize: int) -> None:
        """Initialize."""
        self.file_ = file_
        self.blocksize = blocksize
        self.separator = separator

    def get(self, length: int) -> bytes:
        """Read up to `length` bytes from self.file_."""
        if isinstance(self.file_, int):
            assert isinstance(self.file_, int)
            return os.read(self.file_, length)
        elif isinstance(self.file_, io.IOBase):
            assert isinstance(self.file_, io.IOBase)
            block: bytes = self.file_.read(length)
            return block
        else:
            raise TypeError("self.file_ is neither an int nor a io.IOBase")

    def sequence(self) -> typing.Iterator[bytes]:
        """Generate each field (line) in turn."""
        buffer = b""
        while True:
            chunk = self.get(self.blocksize)
            if not chunk:
                if buffer:
                    yield buffer
                break
            buffer += chunk
            while self.separator in buffer:
                line, buffer = buffer.split(self.separator, 1)
                yield line