def _open(self):
"""
Open the file stream associated with this corpus view. This
will be called performed if any value is read from the view
while its file stream is closed.
"""
if isinstance(self._fileid, PathPointer):
self._stream = self._fileid.open(self._encoding)
elif self._encoding:
self._stream = SeekableUnicodeStreamReader(open(self._fileid, "rb"), self._encoding)
else:
self._stream = open(self._fileid, "rb")
class StreamBackedCorpusView(AbstractLazySequence):
"""
A 'view' of a corpus file, which acts like a sequence of tokens:
it can be accessed by index, iterated over, etc. However, the
tokens are only constructed as-needed -- the entire corpus is
never stored in memory at once.
The constructor to ``StreamBackedCorpusView`` takes two arguments:
a corpus fileid (specified as a string or as a ``PathPointer``);
and a block reader. A "block reader" is a function that reads
zero or more tokens from a stream, and returns them as a list. A
very simple example of a block reader is:
>>> def simple_block_reader(stream):
... return stream.readline().split()
This simple block reader reads a single line at a time, and
returns a single token (consisting of a string) for each
whitespace-separated substring on the line.
When deciding how to define the block reader for a given
corpus, careful consideration should be given to the size of
blocks handled by the block reader. Smaller block sizes will
increase the memory requirements of the corpus view's internal
data structures (by 2 integers per block). On the other hand,
larger block sizes may decrease performance for random access to
the corpus. (But note that larger block sizes will *not*
decrease performance for iteration.)
Internally, ``CorpusView`` maintains a partial mapping from token
index to file position, with one entry per block. When a token
with a given index *i* is requested, the ``CorpusView`` constructs
it as follows:
1. First, it searches the toknum/filepos mapping for the token
index closest to (but less than or equal to) *i*.
2. Then, starting at the file position corresponding to that
index, it reads one block at a time using the block reader
until it reaches the requested token.
The toknum/filepos mapping is created lazily: it is initially
empty, but every time a new block is read, the block's
initial token is added to the mapping. (Thus, the toknum/filepos
map has one entry per block.)
In order to increase efficiency for random access patterns that
have high degrees of locality, the corpus view may cache one or
more blocks.
:note: Each ``CorpusView`` object internally maintains an open file
object for its underlying corpus file. This file should be
automatically closed when the ``CorpusView`` is garbage collected,
but if you wish to close it manually, use the ``close()``
method. If you access a ``CorpusView``'s items after it has been
closed, the file object will be automatically re-opened.
:warning: If the contents of the file are modified during the
lifetime of the ``CorpusView``, then the ``CorpusView``'s behavior
is undefined.
:warning: If a unicode encoding is specified when constructing a
``CorpusView``, then the block reader may only call
``stream.seek()`` with offsets that have been returned by
``stream.tell()``; in particular, calling ``stream.seek()`` with
relative offsets, or with offsets based on string lengths, may
lead to incorrect behavior.
:ivar _block_reader: The function used to read
a single block from the underlying file stream.
:ivar _toknum: A list containing the token index of each block
that has been processed. In particular, ``_toknum[i]`` is the
token index of the first token in block ``i``. Together
with ``_filepos``, this forms a partial mapping between token
indices and file positions.
:ivar _filepos: A list containing the file position of each block
that has been processed. In particular, ``_toknum[i]`` is the
file position of the first character in block ``i``. Together
with ``_toknum``, this forms a partial mapping between token
indices and file positions.
:ivar _stream: The stream used to access the underlying corpus file.
:ivar _len: The total number of tokens in the corpus, if known;
or None, if the number of tokens is not yet known.
:ivar _eofpos: The character position of the last character in the
file. This is calculated when the corpus view is initialized,
and is used to decide when the end of file has been reached.
:ivar _cache: A cache of the most recently read block. It
is encoded as a tuple (start_toknum, end_toknum, tokens), where
start_toknum is the token index of the first token in the block;
end_toknum is the token index of the first token not in the
block; and tokens is a list of the tokens in the block.
"""
def __init__(self, fileid, block_reader=None, startpos=0, encoding="utf8"):
"""
Create a new corpus view, based on the file ``fileid``, and
read with ``block_reader``. See the class documentation
for more information.
:param fileid: The path to the file that is read by this
corpus view. ``fileid`` can either be a string or a
``PathPointer``.
:param startpos: The file position at which the view will
start reading. This can be used to skip over preface
sections.
:param encoding: The unicode encoding that should be used to
read the file's contents. If no encoding is specified,
then the file's contents will be read as a non-unicode
string (i.e., a str).
"""
if block_reader:
self.read_block = block_reader
# Initialize our toknum/filepos mapping.
self._toknum = [0]
self._filepos = [startpos]
self._encoding = encoding
# We don't know our length (number of tokens) yet.
self._len = None
self._fileid = fileid
self._stream = None
self._current_toknum = None
"""This variable is set to the index of the next token that
will be read, immediately before ``self.read_block()`` is
called. This is provided for the benefit of the block
reader, which under rare circumstances may need to know
the current token number."""
self._current_blocknum = None
"""This variable is set to the index of the next block that
will be read, immediately before ``self.read_block()`` is
called. This is provided for the benefit of the block
reader, which under rare circumstances may need to know
the current block number."""
# Find the length of the file.
try:
if isinstance(self._fileid, PathPointer):
self._eofpos = self._fileid.file_size()
else:
self._eofpos = os.stat(self._fileid).st_size
except Exception as exc:
raise ValueError("Unable to open or access %r -- %s" % (fileid, exc))
# Maintain a cache of the most recently read block, to
# increase efficiency of random access.
self._cache = (-1, -1, None)
fileid = property(
lambda self: self._fileid,
doc="""
The fileid of the file that is accessed by this view.
:type: str or PathPointer""",
)
def read_block(self, stream):
"""
Read a block from the input stream.
:return: a block of tokens from the input stream
:rtype: list(any)
:param stream: an input stream
:type stream: stream
"""
raise NotImplementedError("Abstract Method")
def _open(self):
"""
Open the file stream associated with this corpus view. This
will be called performed if any value is read from the view
while its file stream is closed.
"""
if isinstance(self._fileid, PathPointer):
self._stream = self._fileid.open(self._encoding)
elif self._encoding:
self._stream = SeekableUnicodeStreamReader(open(self._fileid, "rb"), self._encoding)
else:
self._stream = open(self._fileid, "rb")
def close(self):
"""
Close the file stream associated with this corpus view. This
can be useful if you are worried about running out of file
handles (although the stream should automatically be closed
upon garbage collection of the corpus view). If the corpus
view is accessed after it is closed, it will be automatically
re-opened.
"""
if self._stream is not None:
self._stream.close()
self._stream = None
def __len__(self):
if self._len is None:
# iterate_from() sets self._len when it reaches the end
# of the file:
for tok in self.iterate_from(self._toknum[-1]):
pass
return self._len
def __getitem__(self, i):
if isinstance(i, slice):
start, stop = slice_bounds(self, i)
# Check if it's in the cache.
offset = self._cache[0]
if offset <= start and stop <= self._cache[1]:
return self._cache[2][start - offset : stop - offset]
# Construct & return the result.
return LazySubsequence(self, start, stop)
else:
# Handle negative indices
if i < 0:
i += len(self)
if i < 0:
raise IndexError("index out of range")
# Check if it's in the cache.
offset = self._cache[0]
if offset <= i < self._cache[1]:
return self._cache[2][i - offset]
# Use iterate_from to extract it.
try:
return next(self.iterate_from(i))
except StopIteration:
raise IndexError("index out of range")
# If we wanted to be thread-safe, then this method would need to
# do some locking.
def iterate_from(self, start_tok):
# Start by feeding from the cache, if possible.
if self._cache[0] <= start_tok < self._cache[1]:
for tok in self._cache[2][start_tok - self._cache[0] :]:
yield tok
start_tok += 1
# Decide where in the file we should start. If `start` is in
# our mapping, then we can jump straight to the correct block;
# otherwise, start at the last block we've processed.
if start_tok < self._toknum[-1]:
block_index = bisect.bisect_right(self._toknum, start_tok) - 1
toknum = self._toknum[block_index]
filepos = self._filepos[block_index]
else:
block_index = len(self._toknum) - 1
toknum = self._toknum[-1]
filepos = self._filepos[-1]
# Open the stream, if it's not open already.
if self._stream is None:
self._open()
# Each iteration through this loop, we read a single block
# from the stream.
while filepos < self._eofpos:
# Read the next block.
self._stream.seek(filepos)
self._current_toknum = toknum
self._current_blocknum = block_index
tokens = self.read_block(self._stream)
assert isinstance(tokens, (tuple, list, AbstractLazySequence)), (
"block reader %s() should return list or tuple." % self.read_block.__name__
)
num_toks = len(tokens)
new_filepos = self._stream.tell()
assert new_filepos > filepos, "block reader %s() should consume at least 1 byte (filepos=%d)" % (
self.read_block.__name__,
filepos,
)
# Update our cache.
self._cache = (toknum, toknum + num_toks, list(tokens))
# Update our mapping.
assert toknum <= self._toknum[-1]
if num_toks > 0:
block_index += 1
if toknum == self._toknum[-1]:
assert new_filepos > self._filepos[-1] # monotonic!
self._filepos.append(new_filepos)
self._toknum.append(toknum + num_toks)
else:
# Check for consistency:
assert new_filepos == self._filepos[block_index], "inconsistent block reader (num chars read)"
assert (
toknum + num_toks == self._toknum[block_index]
), "inconsistent block reader (num tokens returned)"
# If we reached the end of the file, then update self._len
if new_filepos == self._eofpos:
self._len = toknum + num_toks
# Generate the tokens in this block (but skip any tokens
# before start_tok). Note that between yields, our state
# may be modified.
for tok in tokens[max(0, start_tok - toknum) :]:
yield tok
# If we're at the end of the file, then we're done.
assert new_filepos <= self._eofpos
if new_filepos == self._eofpos:
break
# Update our indices
toknum += num_toks
filepos = new_filepos
# If we reach this point, then we should know our length.
assert self._len is not None
# Enforce closing of stream once we reached end of file
# We should have reached EOF once we're out of the while loop.
self.close()
# Use concat for these, so we can use a ConcatenatedCorpusView
# when possible.
def __add__(self, other):
return concat([self, other])
def __radd__(self, other):
return concat([other, self])
def __mul__(self, count):
return concat([self] * count)
def __rmul__(self, count):
return concat([self] * count)
class StreamBackedCorpusView(AbstractLazySequence):
"""
A 'view' of a corpus file, which acts like a sequence of tokens:
it can be accessed by index, iterated over, etc. However, the
tokens are only constructed as-needed -- the entire corpus is
never stored in memory at once.
The constructor to ``StreamBackedCorpusView`` takes two arguments:
a corpus fileid (specified as a string or as a ``PathPointer``);
and a block reader. A "block reader" is a function that reads
zero or more tokens from a stream, and returns them as a list. A
very simple example of a block reader is:
>>> def simple_block_reader(stream):
... return stream.readline().split()
This simple block reader reads a single line at a time, and
returns a single token (consisting of a string) for each
whitespace-separated substring on the line.
When deciding how to define the block reader for a given
corpus, careful consideration should be given to the size of
blocks handled by the block reader. Smaller block sizes will
increase the memory requirements of the corpus view's internal
data structures (by 2 integers per block). On the other hand,
larger block sizes may decrease performance for random access to
the corpus. (But note that larger block sizes will *not*
decrease performance for iteration.)
Internally, ``CorpusView`` maintains a partial mapping from token
index to file position, with one entry per block. When a token
with a given index *i* is requested, the ``CorpusView`` constructs
it as follows:
1. First, it searches the toknum/filepos mapping for the token
index closest to (but less than or equal to) *i*.
2. Then, starting at the file position corresponding to that
index, it reads one block at a time using the block reader
until it reaches the requested token.
The toknum/filepos mapping is created lazily: it is initially
empty, but every time a new block is read, the block's
initial token is added to the mapping. (Thus, the toknum/filepos
map has one entry per block.)
In order to increase efficiency for random access patterns that
have high degrees of locality, the corpus view may cache one or
more blocks.
:note: Each ``CorpusView`` object internally maintains an open file
object for its underlying corpus file. This file should be
automatically closed when the ``CorpusView`` is garbage collected,
but if you wish to close it manually, use the ``close()``
method. If you access a ``CorpusView``'s items after it has been
closed, the file object will be automatically re-opened.
:warning: If the contents of the file are modified during the
lifetime of the ``CorpusView``, then the ``CorpusView``'s behavior
is undefined.
:warning: If a unicode encoding is specified when constructing a
``CorpusView``, then the block reader may only call
``stream.seek()`` with offsets that have been returned by
``stream.tell()``; in particular, calling ``stream.seek()`` with
relative offsets, or with offsets based on string lengths, may
lead to incorrect behavior.
:ivar _block_reader: The function used to read
a single block from the underlying file stream.
:ivar _toknum: A list containing the token index of each block
that has been processed. In particular, ``_toknum[i]`` is the
token index of the first token in block ``i``. Together
with ``_filepos``, this forms a partial mapping between token
indices and file positions.
:ivar _filepos: A list containing the file position of each block
that has been processed. In particular, ``_toknum[i]`` is the
file position of the first character in block ``i``. Together
with ``_toknum``, this forms a partial mapping between token
indices and file positions.
:ivar _stream: The stream used to access the underlying corpus file.
:ivar _len: The total number of tokens in the corpus, if known;
or None, if the number of tokens is not yet known.
:ivar _eofpos: The character position of the last character in the
file. This is calculated when the corpus view is initialized,
and is used to decide when the end of file has been reached.
:ivar _cache: A cache of the most recently read block. It
is encoded as a tuple (start_toknum, end_toknum, tokens), where
start_toknum is the token index of the first token in the block;
end_toknum is the token index of the first token not in the
block; and tokens is a list of the tokens in the block.
"""
def __init__(self, fileid, block_reader=None, startpos=0, encoding="utf8"):
"""
Create a new corpus view, based on the file ``fileid``, and
read with ``block_reader``. See the class documentation
for more information.
:param fileid: The path to the file that is read by this
corpus view. ``fileid`` can either be a string or a
``PathPointer``.
:param startpos: The file position at which the view will
start reading. This can be used to skip over preface
sections.
:param encoding: The unicode encoding that should be used to
read the file's contents. If no encoding is specified,
then the file's contents will be read as a non-unicode
string (i.e., a str).
"""
if block_reader:
self.read_block = block_reader
# Initialize our toknum/filepos mapping.
self._toknum = [0]
self._filepos = [startpos]
self._encoding = encoding
# We don't know our length (number of tokens) yet.
self._len = None
self._fileid = fileid
self._stream = None
self._current_toknum = None
"""This variable is set to the index of the next token that
will be read, immediately before ``self.read_block()`` is
called. This is provided for the benefit of the block
reader, which under rare circumstances may need to know
the current token number."""
self._current_blocknum = None
"""This variable is set to the index of the next block that
will be read, immediately before ``self.read_block()`` is
called. This is provided for the benefit of the block
reader, which under rare circumstances may need to know
the current block number."""
# Find the length of the file.
try:
if isinstance(self._fileid, PathPointer):
self._eofpos = self._fileid.file_size()
else:
self._eofpos = os.stat(self._fileid).st_size
except Exception as exc:
raise ValueError("Unable to open or access %r -- %s" %
(fileid, exc)) from exc
# Maintain a cache of the most recently read block, to
# increase efficiency of random access.
self._cache = (-1, -1, None)
fileid = property(
lambda self: self._fileid,
doc="""
The fileid of the file that is accessed by this view.
:type: str or PathPointer""",
)
def read_block(self, stream):
"""
Read a block from the input stream.
:return: a block of tokens from the input stream
:rtype: list(any)
:param stream: an input stream
:type stream: stream
"""
raise NotImplementedError("Abstract Method")
def _open(self):
"""
Open the file stream associated with this corpus view. This
will be called performed if any value is read from the view
while its file stream is closed.
"""
if isinstance(self._fileid, PathPointer):
self._stream = self._fileid.open(self._encoding)
elif self._encoding:
self._stream = SeekableUnicodeStreamReader(
open(self._fileid, "rb"), self._encoding)
else:
self._stream = open(self._fileid, "rb")
def close(self):
"""
Close the file stream associated with this corpus view. This
can be useful if you are worried about running out of file
handles (although the stream should automatically be closed
upon garbage collection of the corpus view). If the corpus
view is accessed after it is closed, it will be automatically
re-opened.
"""
if self._stream is not None:
self._stream.close()
self._stream = None
def __enter__(self):
return self
def __exit__(self, type, value, traceback):
self.close()
def __len__(self):
if self._len is None:
# iterate_from() sets self._len when it reaches the end
# of the file:
for tok in self.iterate_from(self._toknum[-1]):
pass
return self._len
def __getitem__(self, i):
if isinstance(i, slice):
start, stop = slice_bounds(self, i)
# Check if it's in the cache.
offset = self._cache[0]
if offset <= start and stop <= self._cache[1]:
return self._cache[2][start - offset:stop - offset]
# Construct & return the result.
return LazySubsequence(self, start, stop)
else:
# Handle negative indices
if i < 0:
i += len(self)
if i < 0:
raise IndexError("index out of range")
# Check if it's in the cache.
offset = self._cache[0]
if offset <= i < self._cache[1]:
return self._cache[2][i - offset]
# Use iterate_from to extract it.
try:
return next(self.iterate_from(i))
except StopIteration as e:
raise IndexError("index out of range") from e
# If we wanted to be thread-safe, then this method would need to
# do some locking.
def iterate_from(self, start_tok):
# Start by feeding from the cache, if possible.
if self._cache[0] <= start_tok < self._cache[1]:
for tok in self._cache[2][start_tok - self._cache[0]:]:
yield tok
start_tok += 1
# Decide where in the file we should start. If `start` is in
# our mapping, then we can jump straight to the correct block;
# otherwise, start at the last block we've processed.
if start_tok < self._toknum[-1]:
block_index = bisect.bisect_right(self._toknum, start_tok) - 1
toknum = self._toknum[block_index]
filepos = self._filepos[block_index]
else:
block_index = len(self._toknum) - 1
toknum = self._toknum[-1]
filepos = self._filepos[-1]
# Open the stream, if it's not open already.
if self._stream is None:
self._open()
# If the file is empty, the while loop will never run.
# This *seems* to be all the state we need to set:
if self._eofpos == 0:
self._len = 0
# Each iteration through this loop, we read a single block
# from the stream.
while filepos < self._eofpos:
# Read the next block.
self._stream.seek(filepos)
self._current_toknum = toknum
self._current_blocknum = block_index
tokens = self.read_block(self._stream)
assert isinstance(tokens, (tuple, list, AbstractLazySequence)), (
"block reader %s() should return list or tuple." %
self.read_block.__name__)
num_toks = len(tokens)
new_filepos = self._stream.tell()
assert new_filepos > filepos, (
"block reader %s() should consume at least 1 byte (filepos=%d)"
% (self.read_block.__name__, filepos))
# Update our cache.
self._cache = (toknum, toknum + num_toks, list(tokens))
# Update our mapping.
assert toknum <= self._toknum[-1]
if num_toks > 0:
block_index += 1
if toknum == self._toknum[-1]:
assert new_filepos > self._filepos[-1] # monotonic!
self._filepos.append(new_filepos)
self._toknum.append(toknum + num_toks)
else:
# Check for consistency:
assert (new_filepos == self._filepos[block_index]
), "inconsistent block reader (num chars read)"
assert (
toknum + num_toks == self._toknum[block_index]
), "inconsistent block reader (num tokens returned)"
# If we reached the end of the file, then update self._len
if new_filepos == self._eofpos:
self._len = toknum + num_toks
# Generate the tokens in this block (but skip any tokens
# before start_tok). Note that between yields, our state
# may be modified.
for tok in tokens[max(0, start_tok - toknum):]:
yield tok
# If we're at the end of the file, then we're done.
assert new_filepos <= self._eofpos
if new_filepos == self._eofpos:
break
# Update our indices
toknum += num_toks
filepos = new_filepos
# If we reach this point, then we should know our length.
assert self._len is not None
# Enforce closing of stream once we reached end of file
# We should have reached EOF once we're out of the while loop.
self.close()
# Use concat for these, so we can use a ConcatenatedCorpusView
# when possible.
def __add__(self, other):
return concat([self, other])
def __radd__(self, other):
return concat([other, self])
def __mul__(self, count):
return concat([self] * count)
def __rmul__(self, count):
return concat([self] * count)
assert list(c3[s:]) == l3[s:]
for e in indices:
assert list(c3[:e]) == l3[:e]
print(list(c3[:]) == list(l3[:]))
c3 = StreamBackedCorpusView(f3, read_whitespace_block)
iterators = [c3.iterate_from(n) for n in [0, 15, 30, 45]]
for i in range(15):
for iterator in iterators:
print('%-15s' % next(iterator))
print()
# SeekableUnicodeStreamReader
stream = BytesIO(b"""
This is a test file.
It is encoded in ascii.
""".decode('ascii').encode('ascii'))
reader = SeekableUnicodeStreamReader(stream, 'ascii')
print(reader.read()) # read the entire file.
print(reader.seek(0)) # rewind to the start.
print(reader.read(5)) # read at most 5 bytes.
print(reader.readline()) # read to the end of the line.
print(reader.seek(0)) # rewind to the start.
for line in reader:
print(repr(line)) # iterate over lines
print(reader.seek(0)) # rewind to the start.
print(reader.readlines()) # read a list of line strings
print(reader.close())
# size argument to read()
stream = BytesIO(b"""
This is a test file.
It is encoded in utf-16.
""".decode('ascii').encode('utf-16'))