# Natural Language Toolkit: Utility functions # # Copyright (C) 2001-2010 NLTK Project # Author: Edward Loper # URL: # For license information, see LICENSE.TXT """ Functions to find and load NLTK X{resource files}, such as corpora, grammars, and saved processing objects. Resource files are identified using URLs, such as"C{nltk:corpora/abc/rural.txt}" or "C{http://nltk.org/sample/toy.cfg}". The following URL protocols are supported: - "C{file:I{path}}": Specifies the file whose path is C{I{path}}. Both relative and absolute paths may be used. - "C{http://I{host}/{path}}": Specifies the file stored on the web server C{I{host}} at path C{I{path}}. - "C{nltk:I{path}}": Specifies the file stored in the NLTK data package at C{I{path}}. NLTK will search for these files in the directories specified by L{nltk.data.path}. If no protocol is specified, then the default protocol "C{nltk:}" will be used. This module provides to functions that can be used to access a resource file, given its URL: L{load()} loads a given resource, and adds it to a resource cache; and L{retrieve()} copies a given resource to a local file. """ import sys import os, os.path import textwrap import weakref import yaml import re import urllib2 import zipfile import codecs from gzip import GzipFile, READ as GZ_READ, WRITE as GZ_WRITE try: from zlib import Z_SYNC_FLUSH as FLUSH except: from zlib import Z_FINISH as FLUSH try: import cPickle as pickle except: import pickle try: from cStringIO import StringIO except: from StringIO import StringIO import nltk ###################################################################### # Search Path ###################################################################### path = [] """A list of directories where the NLTK data package might reside. These directories will be checked in order when looking for a resource in the data package. Note that this allows users to substitute in their own versions of resources, if they have them (e.g., in their home directory under ~/nltk_data).""" # User-specified locations: path += [d for d in os.environ.get('NLTK_DATA', '').split(os.pathsep) if d] if os.path.expanduser('~/') != '~/': path += [ os.path.expanduser('~/nltk_data')] # Common locations on Windows: if sys.platform.startswith('win'): path += [ r'C:\nltk_data', r'D:\nltk_data', r'E:\nltk_data', os.path.join(sys.prefix, 'nltk_data'), os.path.join(sys.prefix, 'lib', 'nltk_data'), os.path.join(os.environ.get('APPDATA', 'C:\\'), 'nltk_data')] # Common locations on UNIX & OS X: else: path += [ '/usr/share/nltk_data', '/usr/local/share/nltk_data', '/usr/lib/nltk_data', '/usr/local/lib/nltk_data'] ###################################################################### # Path Pointers ###################################################################### class PathPointer(object): """ An abstract base class for 'path pointers,' used by NLTK's data package to identify specific paths. Two subclasses exist: L{FileSystemPathPointer} identifies a file that can be accessed directly via a given absolute path. L{ZipFilePathPointer} identifies a file contained within a zipfile, that can be accessed by reading that zipfile. """ def open(self, encoding=None): """ Return a seekable read-only stream that can be used to read the contents of the file identified by this path pointer. @raise IOError: If the path specified by this pointer does not contain a readable file. """ raise NotImplementedError('abstract base class') def file_size(self): """ Return the size of the file pointed to by this path pointer, in bytes. @raise IOError: If the path specified by this pointer does not contain a readable file. """ raise NotImplementedError('abstract base class') def join(self, fileid): """ Return a new path pointer formed by starting at the path identified by this pointer, and then following the relative path given by C{fileid}. The path components of C{fileid} should be seperated by forward slashes (C{/}), regardless of the underlying file system's path seperator character. """ raise NotImplementedError('abstract base class') class FileSystemPathPointer(PathPointer, str): """ A path pointer that identifies a file which can be accessed directly via a given absolute path. C{FileSystemPathPointer} is a subclass of C{str} for backwards compatibility purposes -- this allows old code that expected C{nltk.data.find()} to expect a string to usually work (assuming the resource is not found in a zipfile). It also permits open() to work on a FileSystemPathPointer. """ def __init__(self, path): """ Create a new path pointer for the given absolute path. @raise IOError: If the given path does not exist. """ path = os.path.abspath(path) if not os.path.exists(path): raise IOError('No such file or directory: %r' % path) self._path = path # There's no need to call str.__init__(), since it's a no-op; # str does all of its setup work in __new__. path = property(lambda self: self._path, doc=""" The absolute path identified by this path pointer.""") def open(self, encoding=None): stream = open(self._path, 'rb') if encoding is not None: stream = SeekableUnicodeStreamReader(stream, encoding) return stream def file_size(self): return os.stat(self._path).st_size def join(self, fileid): path = os.path.join(self._path, *fileid.split('/')) return FileSystemPathPointer(path) def __repr__(self): return 'FileSystemPathPointer(%r)' % self._path def __str__(self): return self._path class BufferedGzipFile(GzipFile): """ A C{GzipFile} subclass that buffers calls to L{read()} and L{write()}. This allows faster reads and writes of data to and from gzip-compressed files at the cost of using more memory. The default buffer size is 2mb. C{BufferedGzipFile} is useful for loading large gzipped pickle objects as well as writing large encoded feature files for classifier training. """ SIZE = 2 * 2**20 def __init__(self, filename=None, mode=None, compresslevel=9, fileobj=None, **kwargs): """ @return: a buffered gzip file object @rtype: C{BufferedGzipFile} @param filename: a filesystem path @type filename: C{str} @param mode: a file mode which can be any of 'r', 'rb', 'a', 'ab', 'w', or 'wb' @type mode: C{str} @param compresslevel: The compresslevel argument is an integer from 1 to 9 controlling the level of compression; 1 is fastest and produces the least compression, and 9 is slowest and produces the most compression. The default is 9. @type compresslevel: C{int} @param fileobj: a StringIO stream to read from instead of a file. @type fileobj: C{StringIO} @kwparam size: number of bytes to buffer during calls to L{read()} and L{write()} @type size: C{int} """ GzipFile.__init__(self, filename, mode, compresslevel, fileobj) self._size = kwargs.get('size', self.SIZE) self._buffer = StringIO() # cStringIO does not support len. self._len = 0 def _reset_buffer(self): # For some reason calling StringIO.truncate() here will lead to # inconsistent writes so just set _buffer to a new StringIO object. self._buffer = StringIO() self._len = 0 def _write_buffer(self, data): # Simply write to the buffer and increment the buffer size. if data is not None: self._buffer.write(data) self._len += len(data) def _write_gzip(self, data): # Write the current buffer to the GzipFile. GzipFile.write(self, self._buffer.getvalue()) # Then reset the buffer and write the new data to the buffer. self._reset_buffer() self._write_buffer(data) def close(self): # GzipFile.close() doesn't actuallly close anything. if self.mode == GZ_WRITE: self._write_gzip(None) self._reset_buffer() return GzipFile.close(self) def flush(self, lib_mode=FLUSH): self._buffer.flush() GzipFile.flush(self, lib_mode) def read(self, size=None): if not size: size = self._size contents = StringIO() while True: blocks = GzipFile.read(self, size) if not blocks: contents.flush() break contents.write(blocks) return contents.getvalue() else: return GzipFile.read(self, size) def write(self, data, size=-1): """ @param data: C{str} to write to file or buffer @type data: C{str} @param size: buffer at least size bytes before writing to file @type size: C{int} """ if not size: size = self._size if self._len + len(data) <= size: self._write_buffer(data) else: self._write_gzip(data) class GzipFileSystemPathPointer(FileSystemPathPointer): """ A subclass of C{FileSystemPathPointer} that identifies a gzip-compressed file located at a given absolute path. C{GzipFileSystemPathPointer} is appropriate for loading large gzip-compressed pickle objects efficiently. """ def open(self, encoding=None): stream = BufferedGzipFile(self._path, 'rb') if encoding: stream = SeekableUnicodeStreamReader(stream, encoding) return stream class ZipFilePathPointer(PathPointer): """ A path pointer that identifies a file contained within a zipfile, which can be accessed by reading that zipfile. """ def __init__(self, zipfile, entry=''): """ Create a new path pointer pointing at the specified entry in the given zipfile. @raise IOError: If the given zipfile does not exist, or if it does not contain the specified entry. """ if isinstance(zipfile, basestring): zipfile = OpenOnDemandZipFile(os.path.abspath(zipfile)) # Normalize the entry string: entry = re.sub('(^|/)/+', r'\1', entry) # Check that the entry exists: if entry: try: zipfile.getinfo(entry) except: # Sometimes directories aren't explicitly listed in # the zip file. So if `entry` is a directory name, # then check if the zipfile contains any files that # are under the given directory. if (entry.endswith('/') and [n for n in zipfile.namelist() if n.startswith(entry)]): pass # zipfile contains a file in that directory. else: # Otherwise, complain. raise IOError('Zipfile %r does not contain %r' % (zipfile.filename, entry)) self._zipfile = zipfile self._entry = entry zipfile = property(lambda self: self._zipfile, doc=""" The C{zipfile.ZipFile} object used to access the zip file containing the entry identified by this path pointer.""") entry = property(lambda self: self._entry, doc=""" The name of the file within C{zipfile} that this path pointer points to.""") def open(self, encoding=None): data = self._zipfile.read(self._entry) stream = StringIO(data) if self._entry.endswith('.gz'): stream = BufferedGzipFile(self._entry, fileobj=stream) elif encoding is not None: stream = SeekableUnicodeStreamReader(stream, encoding) return stream def file_size(self): return self._zipfile.getinfo(self._entry).file_size def join(self, fileid): entry = '%s/%s' % (self._entry, fileid) return ZipFilePathPointer(self._zipfile, entry) def __repr__(self): return 'ZipFilePathPointer(%r, %r)' % ( self._zipfile.filename, self._entry) ###################################################################### # Access Functions ###################################################################### # Don't use a weak dictionary, because in the common case this # causes a lot more reloading that necessary. _resource_cache = {} """A dictionary used to cache resources so that they won't need to be loaded more than once.""" def find(resource_name): """ Find the given resource by searching through the directories and zip files in L{nltk.data.path}, and return a corresponding path name. If the given resource is not found, raise a C{LookupError}, whose message gives a pointer to the installation instructions for the NLTK downloader. Zip File Handling: - If C{resource_name} contains a component with a C{.zip} extension, then it is assumed to be a zipfile; and the remaining path components are used to look inside the zipfile. - If any element of C{nltk.data.path} has a C{.zip} extension, then it is assumed to be a zipfile. - If a given resource name that does not contain any zipfile component is not found initially, then C{find()} will make a second attempt to find that resource, by replacing each component I{p} in the path with I{p.zip/p}. For example, this allows C{find()} to map the resource name C{corpora/chat80/cities.pl} to a zip file path pointer to C{corpora/chat80.zip/chat80/cities.pl}. - When using C{find()} to locate a directory contained in a zipfile, the resource name I{must} end with the C{'/'} character. Otherwise, C{find()} will not locate the directory. @type resource_name: C{str} @param resource_name: The name of the resource to search for. Resource names are posix-style relative path names, such as C{'corpora/brown'}. In particular, directory names should always be separated by the C{'/'} character, which will be automatically converted to a platform-appropriate path separator. @rtype: C{str} """ # Check if the resource name includes a zipfile name m = re.match('(.*\.zip)/?(.*)$|', resource_name) zipfile, zipentry = m.groups() # Check each item in our path for path_item in path: # Is the path item a zipfile? if os.path.isfile(path_item) and path_item.endswith('.zip'): try: return ZipFilePathPointer(path_item, resource_name) except IOError: continue # resource not in zipfile # Is the path item a directory? elif os.path.isdir(path_item): if zipfile is None: p = os.path.join(path_item, *resource_name.split('/')) if os.path.exists(p): if p.endswith('.gz'): return GzipFileSystemPathPointer(p) else: return FileSystemPathPointer(p) else: p = os.path.join(path_item, *zipfile.split('/')) if os.path.exists(p): try: return ZipFilePathPointer(p, zipentry) except IOError: continue # resource not in zipfile # Fallback: if the path doesn't include a zip file, then try # again, assuming that one of the path components is inside a # zipfile of the same name. if zipfile is None: pieces = resource_name.split('/') for i in range(len(pieces)): modified_name = '/'.join(pieces[:i]+[pieces[i]+'.zip']+pieces[i:]) try: return find(modified_name) except LookupError: pass # Display a friendly error message if the resource wasn't found: msg = textwrap.fill( 'Resource %r not found. Please use the NLTK Downloader to ' 'obtain the resource: >>> nltk.download().' % (resource_name,), initial_indent=' ', subsequent_indent=' ', width=66) msg += '\n Searched in:' + ''.join('\n - %r' % d for d in path) sep = '*'*70 resource_not_found = '\n%s\n%s\n%s' % (sep, msg, sep) raise LookupError(resource_not_found) def retrieve(resource_url, filename=None, verbose=True): """ Copy the given resource to a local file. If no filename is specified, then use the URL's filename. If there is already a file named C{filename}, then raise a C{ValueError}. @type resource_url: C{str} @param resource_url: A URL specifying where the resource should be loaded from. The default protocol is C{"nltk:"}, which searches for the file in the the NLTK data package. """ if filename is None: if resource_url.startswith('file:'): filename = os.path.split(filename)[-1] else: filename = re.sub(r'(^\w+:)?.*/', '', resource_url) if os.path.exists(filename): filename = os.path.abspath(filename) raise ValueError, "File %r already exists!" % filename if verbose: print 'Retrieving %r, saving to %r' % (resource_url, filename) # Open the input & output streams. infile = _open(resource_url) outfile = open(filename, 'wb') # Copy infile -> outfile, using 64k blocks. while True: s = infile.read(1024*64) # 64k blocks. outfile.write(s) if not s: break # Close both files. infile.close() outfile.close() #: A dictionary describing the formats that are supported by NLTK's #: L{load()} method. Keys are format names, and values are format #: descriptions. FORMATS = { 'pickle': "A serialized python object, stored using the pickle module.", 'yaml': "A serialized python object, stored using the yaml module.", 'cfg': "A context free grammar, parsed by nltk.parse_cfg().", 'pcfg': "A probabilistic CFG, parsed by nltk.parse_pcfg().", 'fcfg': "A feature CFG, parsed by nltk.parse_fcfg().", 'fol': "A list of first order logic expressions, parsed by " "nltk.sem.parse_fol() using nltk.sem.logic.LogicParser.", 'logic': "A list of first order logic expressions, parsed by " "nltk.sem.parse_logic(). Requires an additional logic_parser " "parameter", 'val': "A semantic valuation, parsed by nltk.sem.parse_valuation().", 'raw': "The raw (byte string) contents of a file.", } #: A dictionary mapping from file extensions to format names, used #: by L{load()} when C{format="auto"} to decide the format for a #: given resource url. AUTO_FORMATS = { 'pickle': 'pickle', 'yaml': 'yaml', 'cfg': 'cfg', 'pcfg': 'pcfg', 'fcfg': 'fcfg', 'fol': 'fol', 'logic': 'logic', 'val': 'val'} def load(resource_url, format='auto', cache=True, verbose=False, logic_parser=None, fstruct_parser=None): """ Load a given resource from the NLTK data package. The following resource formats are currently supported: - C{'pickle'} - C{'yaml'} - C{'cfg'} (context free grammars) - C{'pcfg'} (probabilistic CFGs) - C{'fcfg'} (feature-based CFGs) - C{'fol'} (formulas of First Order Logic) - C{'logic'} (Logical formulas to be parsed by the given logic_parser) - C{'val'} (valuation of First Order Logic model) - C{'raw'} If no format is specified, C{load()} will attempt to determine a format based on the resource name's file extension. If that fails, C{load()} will raise a C{ValueError} exception. @type resource_url: C{str} @param resource_url: A URL specifying where the resource should be loaded from. The default protocol is C{"nltk:"}, which searches for the file in the the NLTK data package. @type cache: C{bool} @param cache: If true, add this resource to a cache. If C{load} finds a resource in its cache, then it will return it from the cache rather than loading it. The cache uses weak references, so a resource wil automatically be expunged from the cache when no more objects are using it. @type verbose: C{bool} @param verbose: If true, print a message when loading a resource. Messages are not displayed when a resource is retrieved from the cache. @type logic_parser: C{LogicParser} @param logic_parser: The parser that will be used to parse logical expressions. @type fstruct_parser: C{FeatStructParser} @param fstruct_parser: The parser that will be used to parse the feature structure of an fcfg. """ # If we've cached the resource, then just return it. if cache: resource_val = _resource_cache.get(resource_url) if resource_val is not None: if verbose: print '<>' % (resource_url,) return resource_val # Let the user know what's going on. if verbose: print '<>' % (resource_url,) # Determine the format of the resource. if format == 'auto': resource_url_parts = resource_url.split('.') ext = resource_url_parts[-1] if ext == 'gz': ext = resource_url_parts[-2] format = AUTO_FORMATS.get(ext) if format is None: raise ValueError('Could not determine format for %s based ' 'on its file\nextension; use the "format" ' 'argument to specify the format explicitly.' % resource_url) # Load the resource. if format == 'pickle': resource_val = pickle.load(_open(resource_url)) elif format == 'yaml': resource_val = yaml.load(_open(resource_url)) elif format == 'cfg': resource_val = nltk.grammar.parse_cfg(_open(resource_url).read()) elif format == 'pcfg': resource_val = nltk.grammar.parse_pcfg(_open(resource_url).read()) elif format == 'fcfg': resource_val = nltk.grammar.parse_fcfg(_open(resource_url).read(), logic_parser=logic_parser, fstruct_parser=fstruct_parser) elif format == 'fol': resource_val = nltk.sem.parse_logic(_open(resource_url).read(), logic_parser=nltk.sem.logic.LogicParser()) elif format == 'logic': resource_val = nltk.sem.parse_logic(_open(resource_url).read(), logic_parser=logic_parser) elif format == 'val': resource_val = nltk.sem.parse_valuation(_open(resource_url).read()) elif format == 'raw': resource_val = _open(resource_url).read() else: assert format not in FORMATS raise ValueError('Unknown format type!') # If requested, add it to the cache. if cache: try: _resource_cache[resource_url] = resource_val except TypeError: # We can't create weak references to some object types, like # strings and tuples. For now, just don't cache them. pass return resource_val def show_cfg(resource_url, escape='##'): """ Write out a grammar file, ignoring escaped and empty lines @type resource_url: C{str} @param resource_url: A URL specifying where the resource should be loaded from. The default protocol is C{"nltk:"}, which searches for the file in the the NLTK data package. @type escape: C{str} @param escape: Prepended string that signals lines to be ignored """ resource_val = load(resource_url, format='raw', cache=False) lines = resource_val.splitlines() for l in lines: if l.startswith(escape): continue if re.match('^$', l): continue print l def clear_cache(): """ Remove all objects from the resource cache. @see: L{load()} """ _resource_cache.clear() def _open(resource_url): """ Helper function that returns an open file object for a resource, given its resource URL. If the given resource URL uses the 'ntlk' protocol, or uses no protocol, then use L{nltk.data.find} to find its path, and open it with the given mode; if the resource URL uses the 'file' protocol, then open the file with the given mode; otherwise, delegate to C{urllib2.urlopen}. @type resource_url: C{str} @param resource_url: A URL specifying where the resource should be loaded from. The default protocol is C{"nltk:"}, which searches for the file in the the NLTK data package. """ # Divide the resource name into ":". protocol, path = re.match('(?:(\w+):)?(.*)', resource_url).groups() if protocol is None or protocol.lower() == 'nltk': return find(path).open() elif protocol.lower() == 'file': # urllib might not use mode='rb', so handle this one ourselves: return open(path, 'rb') else: return urllib2.urlopen(resource_url) ###################################################################### # Lazy Resource Loader ###################################################################### class LazyLoader(object): def __init__(self, path): self.__path = path def __load(self): resource = load(self.__path) # This is where the magic happens! Transform ourselves into # the object by modifying our own __dict__ and __class__ to # match that of `resource`. self.__dict__ = resource.__dict__ self.__class__ = resource.__class__ def __getattr__(self, attr): self.__load() # This looks circular, but its not, since __load() changes our # __class__ to something new: return getattr(self, attr) def __repr__(self): self.__load() # This looks circular, but its not, since __load() changes our # __class__ to something new: return '%r' % self ###################################################################### # Open-On-Demand ZipFile ###################################################################### class OpenOnDemandZipFile(zipfile.ZipFile): """ A subclass of C{zipfile.ZipFile} that closes its file pointer whenever it is not using it; and re-opens it when it needs to read data from the zipfile. This is useful for reducing the number of open file handles when many zip files are being accessed at once. C{OpenOnDemandZipFile} must be constructed from a filename, not a file-like object (to allow re-opening). C{OpenOnDemandZipFile} is read-only (i.e., C{write} and C{writestr} are disabled. """ def __init__(self, filename): if not isinstance(filename, basestring): raise TypeError('ReopenableZipFile filename must be a string') zipfile.ZipFile.__init__(self, filename) assert self.filename == filename self.close() def read(self, name): assert self.fp is None self.fp = open(self.filename, 'rb') value = zipfile.ZipFile.read(self, name) self.close() return value def write(self, *args, **kwargs): """@raise NotImplementedError: OpenOnDemandZipfile is read-only""" raise NotImplementedError('OpenOnDemandZipfile is read-only') def writestr(self, *args, **kwargs): """@raise NotImplementedError: OpenOnDemandZipfile is read-only""" raise NotImplementedError('OpenOnDemandZipfile is read-only') def __repr__(self): return 'OpenOnDemandZipFile(%r)' % self.filename ###################################################################### #{ Seekable Unicode Stream Reader ###################################################################### class SeekableUnicodeStreamReader(object): """ A stream reader that automatically encodes the source byte stream into unicode (like C{codecs.StreamReader}); but still supports the C{seek()} and C{tell()} operations correctly. This is in contrast to C{codecs.StreamReader}, which provide *broken* C{seek()} and C{tell()} methods. This class was motivated by L{StreamBackedCorpusView}, which makes extensive use of C{seek()} and C{tell()}, and needs to be able to handle unicode-encoded files. Note: this class requires stateless decoders. To my knowledge, this shouldn't cause a problem with any of python's builtin unicode encodings. """ DEBUG = True #: If true, then perform extra sanity checks. def __init__(self, stream, encoding, errors='strict'): # Rewind the stream to its beginning. stream.seek(0) self.stream = stream """The underlying stream.""" self.encoding = encoding """The name of the encoding that should be used to encode the underlying stream.""" self.errors = errors """The error mode that should be used when decoding data from the underlying stream. Can be 'strict', 'ignore', or 'replace'.""" self.decode = codecs.getdecoder(encoding) """The function that is used to decode byte strings into unicode strings.""" self.bytebuffer = '' """A buffer to use bytes that have been read but have not yet been decoded. This is only used when the final bytes from a read do not form a complete encoding for a character.""" self.linebuffer = None """A buffer used by L{readline()} to hold characters that have been read, but have not yet been returned by L{read()} or L{readline()}. This buffer consists of a list of unicode strings, where each string corresponds to a single line. The final element of the list may or may not be a complete line. Note that the existence of a linebuffer makes the L{tell()} operation more complex, because it must backtrack to the beginning of the buffer to determine the correct file position in the underlying byte stream.""" self._rewind_checkpoint = 0 """The file position at which the most recent read on the underlying stream began. This is used, together with L{_rewind_numchars}, to backtrack to the beginning of L{linebuffer} (which is required by L{tell()}).""" self._rewind_numchars = None """The number of characters that have been returned since the read that started at L{_rewind_checkpoint}. This is used, together with L{_rewind_checkpoint}, to backtrack to the beginning of L{linebuffer} (which is required by L{tell()}).""" self._bom = self._check_bom() """The length of the byte order marker at the beginning of the stream (or C{None} for no byte order marker).""" #///////////////////////////////////////////////////////////////// # Read methods #///////////////////////////////////////////////////////////////// def read(self, size=None): """ Read up to C{size} bytes, decode them using this reader's encoding, and return the resulting unicode string. @param size: The maximum number of bytes to read. If not specified, then read as many bytes as possible. @rtype: C{unicode} """ chars = self._read(size) # If linebuffer is not empty, then include it in the result if self.linebuffer: chars = ''.join(self.linebuffer) + chars self.linebuffer = None self._rewind_numchars = None return chars def readline(self, size=None): """ Read a line of text, decode it using this reader's encoding, and return the resulting unicode string. @param size: The maximum number of bytes to read. If no newline is encountered before C{size} bytes have been read, then the returned value may not be a complete line of text. """ # If we have a non-empty linebuffer, then return the first # line from it. (Note that the last element of linebuffer may # not be a complete line; so let _read() deal with it.) if self.linebuffer and len(self.linebuffer) > 1: line = self.linebuffer.pop(0) self._rewind_numchars += len(line) return line readsize = size or 72 chars = '' # If there's a remaining incomplete line in the buffer, add it. if self.linebuffer: chars += self.linebuffer.pop() self.linebuffer = None while True: startpos = self.stream.tell() - len(self.bytebuffer) new_chars = self._read(readsize) # If we're at a '\r', then read one extra character, since # it might be a '\n', to get the proper line ending. if new_chars and new_chars.endswith('\r'): new_chars += self._read(1) chars += new_chars lines = chars.splitlines(True) if len(lines) > 1: line = lines[0] self.linebuffer = lines[1:] self._rewind_numchars = len(new_chars)-(len(chars)-len(line)) self._rewind_checkpoint = startpos break elif len(lines) == 1: line0withend = lines[0] line0withoutend = lines[0].splitlines(False)[0] if line0withend != line0withoutend: # complete line line = line0withend break if not new_chars or size is not None: line = chars break # Read successively larger blocks of text. if readsize < 8000: readsize *= 2 return line def readlines(self, sizehint=None, keepends=True): """ Read this file's contents, decode them using this reader's encoding, and return it as a list of unicode lines. @rtype: C{list} of C{unicode} @param sizehint: Ignored. @param keepends: If false, then strip newlines. """ return self.read().splitlines(keepends) def next(self): """Return the next decoded line from the underlying stream.""" line = self.readline() if line: return line else: raise StopIteration def __iter__(self): """Return self""" return self def xreadlines(self): """Return self""" return self #///////////////////////////////////////////////////////////////// # Pass-through methods & properties #///////////////////////////////////////////////////////////////// closed = property(lambda self: self.stream.closed, doc=""" True if the underlying stream is closed.""") name = property(lambda self: self.stream.name, doc=""" The name of the underlying stream.""") mode = property(lambda self: self.stream.mode, doc=""" The mode of the underlying stream.""") def close(self): """ Close the underlying stream. """ self.stream.close() #///////////////////////////////////////////////////////////////// # Seek and tell #///////////////////////////////////////////////////////////////// def seek(self, offset, whence=0): """ Move the stream to a new file position. If the reader is maintaining any buffers, tehn they will be cleared. @param offset: A byte count offset. @param whence: If C{whence} is 0, then the offset is from the start of the file (offset should be positive). If C{whence} is 1, then the offset is from the current position (offset may be positive or negative); and if 2, then the offset is from the end of the file (offset should typically be negative). """ if whence == 1: raise ValueError('Relative seek is not supported for ' 'SeekableUnicodeStreamReader -- consider ' 'using char_seek_forward() instead.') self.stream.seek(offset, whence) self.linebuffer = None self.bytebuffer = '' self._rewind_numchars = None self._rewind_checkpoint = self.stream.tell() def char_seek_forward(self, offset): """ Move the read pointer forward by C{offset} characters. """ if offset < 0: raise ValueError('Negative offsets are not supported') # Clear all buffers. self.seek(self.tell()) # Perform the seek operation. self._char_seek_forward(offset) def _char_seek_forward(self, offset, est_bytes=None): """ Move the file position forward by C{offset} characters, ignoring all buffers. @param est_bytes: A hint, giving an estimate of the number of bytes that will be neded to move foward by C{offset} chars. Defaults to C{offset}. """ if est_bytes is None: est_bytes = offset bytes = '' while True: # Read in a block of bytes. newbytes = self.stream.read(est_bytes-len(bytes)) bytes += newbytes # Decode the bytes to characters. chars, bytes_decoded = self._incr_decode(bytes) # If we got the right number of characters, then seek # backwards over any truncated characters, and return. if len(chars) == offset: self.stream.seek(-len(bytes)+bytes_decoded, 1) return # If we went too far, then we can back-up until we get it # right, using the bytes we've already read. if len(chars) > offset: while len(chars) > offset: # Assume at least one byte/char. est_bytes += offset-len(chars) chars, bytes_decoded = self._incr_decode(bytes[:est_bytes]) self.stream.seek(-len(bytes)+bytes_decoded, 1) return # Otherwise, we haven't read enough bytes yet; loop again. est_bytes += offset - len(chars) def tell(self): """ Return the current file position on the underlying byte stream. If this reader is maintaining any buffers, then the returned file position will be the position of the beginning of those buffers. """ # If nothing's buffered, then just return our current filepos: if self.linebuffer is None: return self.stream.tell() - len(self.bytebuffer) # Otherwise, we'll need to backtrack the filepos until we # reach the beginning of the buffer. # Store our original file position, so we can return here. orig_filepos = self.stream.tell() # Calculate an estimate of where we think the newline is. bytes_read = ( (orig_filepos-len(self.bytebuffer)) - self._rewind_checkpoint ) buf_size = sum([len(line) for line in self.linebuffer]) est_bytes = (bytes_read * self._rewind_numchars / (self._rewind_numchars + buf_size)) self.stream.seek(self._rewind_checkpoint) self._char_seek_forward(self._rewind_numchars, est_bytes) filepos = self.stream.tell() # Sanity check if self.DEBUG: self.stream.seek(filepos) check1 = self._incr_decode(self.stream.read(50))[0] check2 = ''.join(self.linebuffer) assert check1.startswith(check2) or check2.startswith(check1) # Return to our original filepos (so we don't have to throw # out our buffer.) self.stream.seek(orig_filepos) # Return the calculated filepos return filepos #///////////////////////////////////////////////////////////////// # Helper methods #///////////////////////////////////////////////////////////////// def _read(self, size=None): """ Read up to C{size} bytes from the underlying stream, decode them using this reader's encoding, and return the resulting unicode string. C{linebuffer} is *not* included in the result. """ if size == 0: return u'' # Skip past the byte order marker, if present. if self._bom and self.stream.tell() == 0: self.stream.read(self._bom) # Read the requested number of bytes. if size is None: new_bytes = self.stream.read() else: new_bytes = self.stream.read(size) bytes = self.bytebuffer + new_bytes # Decode the bytes into unicode characters chars, bytes_decoded = self._incr_decode(bytes) # If we got bytes but couldn't decode any, then read further. if (size is not None) and (not chars) and (len(new_bytes) > 0): while not chars: new_bytes = self.stream.read(1) if not new_bytes: break # end of file. bytes += new_bytes chars, bytes_decoded = self._incr_decode(bytes) # Record any bytes we didn't consume. self.bytebuffer = bytes[bytes_decoded:] # Return the result return chars def _incr_decode(self, bytes): """ Decode the given byte string into a unicode string, using this reader's encoding. If an exception is encountered that appears to be caused by a truncation error, then just decode the byte string without the bytes that cause the trunctaion error. @return: A tuple C{(chars, num_consumed)}, where C{chars} is the decoded unicode string, and C{num_consumed} is the number of bytes that were consumed. """ while True: try: return self.decode(bytes, 'strict') except UnicodeDecodeError, exc: # If the exception occurs at the end of the string, # then assume that it's a truncation error. if exc.end == len(bytes): return self.decode(bytes[:exc.start], self.errors) # Otherwise, if we're being strict, then raise it. elif self.errors == 'strict': raise # If we're not strcit, then re-process it with our # errors setting. This *may* raise an exception. else: return self.decode(bytes, self.errors) _BOM_TABLE = { 'utf8': [(codecs.BOM_UTF8, None)], 'utf16': [(codecs.BOM_UTF16_LE, 'utf16-le'), (codecs.BOM_UTF16_BE, 'utf16-be')], 'utf16le': [(codecs.BOM_UTF16_LE, None)], 'utf16be': [(codecs.BOM_UTF16_BE, None)], 'utf32': [(codecs.BOM_UTF32_LE, 'utf32-le'), (codecs.BOM_UTF32_BE, 'utf32-be')], 'utf32le': [(codecs.BOM_UTF32_LE, None)], 'utf32be': [(codecs.BOM_UTF32_BE, None)], } def _check_bom(self): # Normalize our encoding name enc = re.sub('[ -]', '', self.encoding.lower()) # Look up our encoding in the BOM table. bom_info = self._BOM_TABLE.get(enc) if bom_info: # Read a prefix, to check against the BOM(s) bytes = self.stream.read(16) self.stream.seek(0) # Check for each possible BOM. for (bom, new_encoding) in bom_info: if bytes.startswith(bom): if new_encoding: self.encoding = new_encoding return len(bom) return None __all__ = ['path', 'PathPointer', 'FileSystemPathPointer', 'BufferedGzipFile', 'GzipFileSystemPathPointer', 'GzipFileSystemPathPointer', 'find', 'retrieve', 'FORMATS', 'AUTO_FORMATS', 'load', 'show_cfg', 'clear_cache', 'LazyLoader', 'OpenOnDemandZipFile', 'GzipFileSystemPathPointer', 'SeekableUnicodeStreamReader']