# Natural Language Toolkit: Utility functions # # Copyright (C) 2001-2010 NLTK Project # Author: Steven Bird # URL: # For license information, see LICENSE.TXT import locale import re import types import textwrap import pydoc import bisect import os from itertools import islice, chain from pprint import pprint from nltk.compat import defaultdict from nltk.internals import Deprecated, slice_bounds ###################################################################### # Short usage message ###################################################################### def usage(obj, selfname='self'): import inspect str(obj) # In case it's lazy, this will load it. if not isinstance(obj, (types.TypeType, types.ClassType)): obj = obj.__class__ print '%s supports the following operations:' % obj.__name__ for (name, method) in sorted(pydoc.allmethods(obj).items()): if name.startswith('_'): continue if getattr(method, '__deprecated__', False): continue args, varargs, varkw, defaults = inspect.getargspec(method) if (args and args[0]=='self' and (defaults is None or len(args)>len(defaults))): args = args[1:] name = '%s.%s' % (selfname, name) argspec = inspect.formatargspec( args, varargs, varkw, defaults) print textwrap.fill('%s%s' % (name, argspec), initial_indent=' - ', subsequent_indent=' '*(len(name)+5)) ########################################################################## # IDLE ########################################################################## def in_idle(): """ @rtype: C{boolean} @return: true if this function is run within idle. Tkinter programs that are run in idle should never call C{Tk.mainloop}; so this function should be used to gate all calls to C{Tk.mainloop}. @warning: This function works by checking C{sys.stdin}. If the user has modified C{sys.stdin}, then it may return incorrect results. """ import sys, types return (type(sys.stdin) == types.InstanceType and \ sys.stdin.__class__.__name__ == 'PyShell') ########################################################################## # PRETTY PRINTING ########################################################################## def pr(data, start=0, end=None): """ Pretty print a sequence of data items @param data: the data stream to print @type data: C{sequence} or C{iterator} @param start: the start position @type start: C{int} @param end: the end position @type end: C{int} """ pprint(list(islice(data, start, end))) def print_string(s, width=70): """ Pretty print a string, breaking lines on whitespace @param s: the string to print, consisting of words and spaces @type s: C{string} @param width: the display width @type width: C{int} """ print '\n'.join(textwrap.wrap(s, width=width)) def tokenwrap(tokens, separator=" ", width=70): """ Pretty print a list of text tokens, breaking lines on whitespace @param tokens: the tokens to print @type tokens: C{list} @param separator: the string to use to separate tokens @type separator: C{str} @param width: the display width (default=70) @type width: C{int} """ return '\n'.join(textwrap.wrap(separator.join(tokens), width=width)) ########################################################################## # Indexing ########################################################################## class Index(defaultdict): def __init__(self, pairs): defaultdict.__init__(self, list) for key, value in pairs: self[key].append(value) ###################################################################### ## Regexp display (thanks to David Mertz) ###################################################################### def re_show(regexp, string, left="{", right="}"): """ Search C{string} for substrings matching C{regexp} and wrap the matches with braces. This is convenient for learning about regular expressions. @param regexp: The regular expression. @type regexp: C{string} @param string: The string being matched. @type string: C{string} @param left: The left delimiter (printed before the matched substring) @type left: C{string} @param right: The right delimiter (printed after the matched substring) @type right: C{string} @rtype: C{string} @return: A string with markers surrounding the matched substrings. """ print re.compile(regexp, re.M).sub(left + r"\g<0>" + right, string.rstrip()) ########################################################################## # READ FROM FILE OR STRING ########################################################################## # recipe from David Mertz def filestring(f): if hasattr(f, 'read'): return f.read() elif isinstance(f, basestring): return open(f).read() else: raise ValueError, "Must be called with a filename or file-like object" ########################################################################## # Breadth-First Search ########################################################################## def breadth_first(tree, children=iter, depth=-1, queue=None): """Traverse the nodes of a tree in breadth-first order. (No need to check for cycles.) The first argument should be the tree root; children should be a function taking as argument a tree node and returning an iterator of the node's children. """ if queue == None: queue = [] queue.append(tree) while queue: node = queue.pop(0) yield node if depth != 0: try: queue += children(node) depth -= 1 except: pass ########################################################################## # Guess Character Encoding ########################################################################## # adapted from io.py in the docutils extension module (http://docutils.sourceforge.net) # http://www.pyzine.com/Issue008/Section_Articles/article_Encodings.html def guess_encoding(data): """ Given a byte string, attempt to decode it. Tries the standard 'UTF8' and 'latin-1' encodings, Plus several gathered from locale information. The calling program *must* first call:: locale.setlocale(locale.LC_ALL, '') If successful it returns C{(decoded_unicode, successful_encoding)}. If unsuccessful it raises a C{UnicodeError}. """ successful_encoding = None # we make 'utf-8' the first encoding encodings = ['utf-8'] # # next we add anything we can learn from the locale try: encodings.append(locale.nl_langinfo(locale.CODESET)) except AttributeError: pass try: encodings.append(locale.getlocale()[1]) except (AttributeError, IndexError): pass try: encodings.append(locale.getdefaultlocale()[1]) except (AttributeError, IndexError): pass # # we try 'latin-1' last encodings.append('latin-1') for enc in encodings: # some of the locale calls # may have returned None if not enc: continue try: decoded = unicode(data, enc) successful_encoding = enc except (UnicodeError, LookupError): pass else: break if not successful_encoding: raise UnicodeError( 'Unable to decode input data. Tried the following encodings: %s.' % ', '.join([repr(enc) for enc in encodings if enc])) else: return (decoded, successful_encoding) ########################################################################## # Invert a dictionary ########################################################################## def invert_dict(d): from nltk.compat import defaultdict inverted_dict = defaultdict(list) for key in d: if hasattr(d[key], '__iter__'): for term in d[key]: inverted_dict[term].append(key) else: inverted_dict[d[key]] = key return inverted_dict ########################################################################## # Utilities for directed graphs: transitive closure, and inversion # The graph is represented as a dictionary of sets ########################################################################## def transitive_closure(graph, reflexive=False): """ Calculate the transitive closure of a directed graph, optionally the reflexive transitive closure. The algorithm is a slight modification of the "Marking Algorithm" of Ioannidis & Ramakrishnan (1998) "Efficient Transitive Closure Algorithms". @param graph: the initial graph, represented as a dictionary of sets @type graph: C{dict} of C{set}s @param reflexive: if set, also make the closure reflexive @type reflexive: C{bool} @return: the (reflexive) transitive closure of the graph @rtype: C{dict} of C{set}s """ if reflexive: base_set = lambda k: set([k]) else: base_set = lambda k: set() # The graph U_i in the article: agenda_graph = dict((k, v.copy()) for (k,v) in graph.iteritems()) # The graph M_i in the article: closure_graph = dict((k, base_set(k)) for k in graph) for i in graph: agenda = agenda_graph[i] closure = closure_graph[i] while agenda: j = agenda.pop() closure.add(j) closure |= closure_graph.setdefault(j, base_set(j)) agenda |= agenda_graph.get(j, base_set(j)) agenda -= closure return closure_graph def invert_graph(graph): """ Inverts a directed graph. @param graph: the graph, represented as a dictionary of sets @type graph: C{dict} of C{set}s @return: the inverted graph @rtype: C{dict} of C{set}s """ inverted = {} for key, values in graph.iteritems(): for value in values: inverted.setdefault(value, set()).add(key) return inverted ########################################################################## # HTML Cleaning ########################################################################## def clean_html(html): """ Remove HTML markup from the given string. @param html: the HTML string to be cleaned @type html: C{string} @rtype: C{string} """ # First we remove inline JavaScript/CSS: cleaned = re.sub(r"(?is)<(script|style).*?>.*?()", "", html.strip()) # Then we remove html comments. This has to be done before removing regular # tags since comments can contain '>' characters. cleaned = re.sub(r"(?s)[\n]?", "", cleaned) # Next we can remove the remaining tags: cleaned = re.sub(r"(?s)<.*?>", " ", cleaned) # Finally, we deal with whitespace cleaned = re.sub(r" ", " ", cleaned) cleaned = re.sub(r" ", " ", cleaned) cleaned = re.sub(r" ", " ", cleaned) return cleaned.strip() def clean_url(url): from urllib import urlopen html = urlopen(url).read() return clean_html(html) ########################################################################## # Ngram iteration ########################################################################## # add a flag to pad the sequence so we get peripheral ngrams? def ngrams(sequence, n, pad_left=False, pad_right=False, pad_symbol=None): """ A utility that produces a sequence of ngrams from a sequence of items. For example: >>> ngrams([1,2,3,4,5], 3) [(1, 2, 3), (2, 3, 4), (3, 4, 5)] Use ingram for an iterator version of this function. Set pad_left or pad_right to true in order to get additional ngrams: >>> ngrams([1,2,3,4,5], 2, pad_right=True) [(1, 2), (2, 3), (3, 4), (4, 5), (5, None)] @param sequence: the source data to be converted into ngrams @type sequence: C{sequence} or C{iterator} @param n: the degree of the ngrams @type n: C{int} @param pad_left: whether the ngrams should be left-padded @type pad_left: C{boolean} @param pad_right: whether the ngrams should be right-padded @type pad_right: C{boolean} @param pad_symbol: the symbol to use for padding (default is None) @type pad_symbol: C{any} @return: The ngrams @rtype: C{list} of C{tuple}s """ if pad_left: sequence = chain((pad_symbol,) * (n-1), sequence) if pad_right: sequence = chain(sequence, (pad_symbol,) * (n-1)) sequence = list(sequence) count = max(0, len(sequence) - n + 1) return [tuple(sequence[i:i+n]) for i in range(count)] def bigrams(sequence, **kwargs): """ A utility that produces a sequence of bigrams from a sequence of items. For example: >>> bigrams([1,2,3,4,5]) [(1, 2), (2, 3), (3, 4), (4, 5)] Use ibigrams for an iterator version of this function. @param sequence: the source data to be converted into bigrams @type sequence: C{sequence} or C{iterator} @return: The bigrams @rtype: C{list} of C{tuple}s """ return ngrams(sequence, 2, **kwargs) def trigrams(sequence, **kwargs): """ A utility that produces a sequence of trigrams from a sequence of items. For example: >>> trigrams([1,2,3,4,5]) [(1, 2, 3), (2, 3, 4), (3, 4, 5)] Use itrigrams for an iterator version of this function. @param sequence: the source data to be converted into trigrams @type sequence: C{sequence} or C{iterator} @return: The trigrams @rtype: C{list} of C{tuple}s """ return ngrams(sequence, 3, **kwargs) def ingrams(sequence, n, pad_left=False, pad_right=False, pad_symbol=None): """ A utility that produces an iterator over ngrams generated from a sequence of items. For example: >>> list(ingrams([1,2,3,4,5], 3)) [(1, 2, 3), (2, 3, 4), (3, 4, 5)] Use ngrams for a list version of this function. Set pad_left or pad_right to true in order to get additional ngrams: >>> list(ingrams([1,2,3,4,5], 2, pad_right=True)) [(1, 2), (2, 3), (3, 4), (4, 5), (5, None)] @param sequence: the source data to be converted into ngrams @type sequence: C{sequence} or C{iterator} @param n: the degree of the ngrams @type n: C{int} @param pad_left: whether the ngrams should be left-padded @type pad_left: C{boolean} @param pad_right: whether the ngrams should be right-padded @type pad_right: C{boolean} @param pad_symbol: the symbol to use for padding (default is None) @type pad_symbol: C{any} @return: The ngrams @rtype: C{iterator} of C{tuple}s """ sequence = iter(sequence) if pad_left: sequence = chain((pad_symbol,) * (n-1), sequence) if pad_right: sequence = chain(sequence, (pad_symbol,) * (n-1)) history = [] while n > 1: history.append(sequence.next()) n -= 1 for item in sequence: history.append(item) yield tuple(history) del history[0] def ibigrams(sequence, **kwargs): """ A utility that produces an iterator over bigrams generated from a sequence of items. For example: >>> list(ibigrams([1,2,3,4,5])) [(1, 2), (2, 3), (3, 4), (4, 5)] Use bigrams for a list version of this function. @param sequence: the source data to be converted into bigrams @type sequence: C{sequence} or C{iterator} @return: The bigrams @rtype: C{iterator} of C{tuple}s """ for item in ingrams(sequence, 2, **kwargs): yield item def itrigrams(sequence, **kwargs): """ A utility that produces an iterator over trigrams generated from a sequence of items. For example: >>> list(itrigrams([1,2,3,4,5]) [(1, 2, 3), (2, 3, 4), (3, 4, 5)] Use trigrams for a list version of this function. @param sequence: the source data to be converted into trigrams @type sequence: C{sequence} or C{iterator} @return: The trigrams @rtype: C{iterator} of C{tuple}s """ for item in ingrams(sequence, 3, **kwargs): yield item ########################################################################## # Ordered Dictionary ########################################################################## class OrderedDict(dict): def __init__(self, data=None, **kwargs): self._keys = self.keys(data, kwargs.get('keys')) self._default_factory = kwargs.get('default_factory') if data is None: dict.__init__(self) else: dict.__init__(self, data) def __delitem__(self, key): dict.__delitem__(self, key) self._keys.remove(key) def __getitem__(self, key): try: return dict.__getitem__(self, key) except KeyError: return self.__missing__(key) def __iter__(self): return (key for key in self.keys()) def __missing__(self, key): if not self._default_factory and key not in self._keys: raise KeyError() else: return self._default_factory() def __setitem__(self, key, item): dict.__setitem__(self, key, item) if key not in self._keys: self._keys.append(key) def clear(self): dict.clear(self) self._keys.clear() def copy(self): d = dict.copy(self) d._keys = self._keys return d def items(self): return zip(self.keys(), self.values()) def keys(self, data=None, keys=None): if data: if keys: assert isinstance(keys, list) assert len(data) == len(keys) return keys else: assert isinstance(data, dict) or \ isinstance(data, OrderedDict) or \ isinstance(data, list) if isinstance(data, dict) or isinstance(data, OrderedDict): return data.keys() elif isinstance(data, list): return [key for (key, value) in data] elif '_keys' in self.__dict__: return self._keys else: return [] def popitem(self): if self._keys: key = self._keys.pop() value = self[key] del self[key] return (key, value) else: raise KeyError() def setdefault(self, key, failobj=None): dict.setdefault(self, key, failobj) if key not in self._keys: self._keys.append(key) def update(self, data): dict.update(self, data) for key in self.keys(data): if key not in self._keys: self._keys.append(key) def values(self): return map(self.get, self._keys) ###################################################################### # Lazy Sequences ###################################################################### class AbstractLazySequence(object): """ An abstract base class for read-only sequences whose values are computed as needed. Lazy sequences act like tuples -- they can be indexed, sliced, and iterated over; but they may not be modified. The most common application of lazy sequences in NLTK is for I{corpus view} objects, which provide access to the contents of a corpus without loading the entire corpus into memory, by loading pieces of the corpus from disk as needed. The result of modifying a mutable element of a lazy sequence is undefined. In particular, the modifications made to the element may or may not persist, depending on whether and when the lazy sequence caches that element's value or reconstructs it from scratch. Subclasses are required to define two methods: - L{__len__()} - L{iterate_from()}. """ def __len__(self): """ Return the number of tokens in the corpus file underlying this corpus view. """ raise NotImplementedError('should be implemented by subclass') def iterate_from(self, start): """ Return an iterator that generates the tokens in the corpus file underlying this corpus view, starting at the token number C{start}. If C{start>=len(self)}, then this iterator will generate no tokens. """ raise NotImplementedError('should be implemented by subclass') def __getitem__(self, i): """ Return the C{i}th token in the corpus file underlying this corpus view. Negative indices and spans are both supported. """ if isinstance(i, slice): start, stop = slice_bounds(self, i) return LazySubsequence(self, start, stop) else: # Handle negative indices if i < 0: i += len(self) if i < 0: raise IndexError('index out of range') # Use iterate_from to extract it. try: return self.iterate_from(i).next() except StopIteration: raise IndexError('index out of range') def __iter__(self): """Return an iterator that generates the tokens in the corpus file underlying this corpus view.""" return self.iterate_from(0) def count(self, value): """Return the number of times this list contains C{value}.""" return sum(1 for elt in self if elt==value) def index(self, value, start=None, stop=None): """Return the index of the first occurance of C{value} in this list that is greater than or equal to C{start} and less than C{stop}. Negative start & stop values are treated like negative slice bounds -- i.e., they count from the end of the list.""" start, stop = slice_bounds(self, slice(start, stop)) for i, elt in enumerate(islice(self, start, stop)): if elt == value: return i+start raise ValueError('index(x): x not in list') def __contains__(self, value): """Return true if this list contains C{value}.""" return bool(self.count(value)) def __add__(self, other): """Return a list concatenating self with other.""" return LazyConcatenation([self, other]) def __radd__(self, other): """Return a list concatenating other with self.""" return LazyConcatenation([other, self]) def __mul__(self, count): """Return a list concatenating self with itself C{count} times.""" return LazyConcatenation([self] * count) def __rmul__(self, count): """Return a list concatenating self with itself C{count} times.""" return LazyConcatenation([self] * count) _MAX_REPR_SIZE = 60 def __repr__(self): """ @return: A string representation for this corpus view that is similar to a list's representation; but if it would be more than 60 characters long, it is truncated. """ pieces = [] length = 5 for elt in self: pieces.append(repr(elt)) length += len(pieces[-1]) + 2 if length > self._MAX_REPR_SIZE and len(pieces) > 2: return '[%s, ...]' % ', '.join(pieces[:-1]) else: return '[%s]' % ', '.join(pieces) def __cmp__(self, other): """ Return a number indicating how C{self} relates to other. - If C{other} is not a corpus view or a C{list}, return -1. - Otherwise, return C{cmp(list(self), list(other))}. Note: corpus views do not compare equal to tuples containing equal elements. Otherwise, transitivity would be violated, since tuples do not compare equal to lists. """ if not isinstance(other, (AbstractLazySequence, list)): return -1 return cmp(list(self), list(other)) def __hash__(self): """ @raise ValueError: Corpus view objects are unhashable. """ raise ValueError('%s objects are unhashable' % self.__class__.__name__) class LazySubsequence(AbstractLazySequence): """ A subsequence produced by slicing a lazy sequence. This slice keeps a reference to its source sequence, and generates its values by looking them up in the source sequence. """ MIN_SIZE = 100 """The minimum size for which lazy slices should be created. If C{LazySubsequence()} is called with a subsequence that is shorter than C{MIN_SIZE}, then a tuple will be returned instead.""" def __new__(cls, source, start, stop): """ Construct a new slice from a given underlying sequence. The C{start} and C{stop} indices should be absolute indices -- i.e., they should not be negative (for indexing from the back of a list) or greater than the length of C{source}. """ # If the slice is small enough, just use a tuple. if stop-start < cls.MIN_SIZE: return list(islice(source.iterate_from(start), stop-start)) else: return object.__new__(cls) def __init__(self, source, start, stop): self._source = source self._start = start self._stop = stop def __len__(self): return self._stop - self._start def iterate_from(self, start): return islice(self._source.iterate_from(start+self._start), max(0, len(self)-start)) class LazyConcatenation(AbstractLazySequence): """ A lazy sequence formed by concatenating a list of lists. This underlying list of lists may itself be lazy. C{LazyConcatenation} maintains an index that it uses to keep track of the relationship between offsets in the concatenated lists and offsets in the sublists. """ def __init__(self, list_of_lists): self._list = list_of_lists self._offsets = [0] def __len__(self): if len(self._offsets) <= len(self._list): for tok in self.iterate_from(self._offsets[-1]): pass return self._offsets[-1] def iterate_from(self, start_index): if start_index < self._offsets[-1]: sublist_index = bisect.bisect_right(self._offsets, start_index)-1 else: sublist_index = len(self._offsets)-1 index = self._offsets[sublist_index] # Construct an iterator over the sublists. if isinstance(self._list, AbstractLazySequence): sublist_iter = self._list.iterate_from(sublist_index) else: sublist_iter = islice(self._list, sublist_index, None) for sublist in sublist_iter: if sublist_index == (len(self._offsets)-1): assert index+len(sublist) >= self._offsets[-1], ( 'offests not monotonic increasing!') self._offsets.append(index+len(sublist)) else: assert self._offsets[sublist_index+1] == index+len(sublist), ( 'inconsistent list value (num elts)') for value in sublist[max(0, start_index-index):]: yield value index += len(sublist) sublist_index += 1 class LazyMap(AbstractLazySequence): """ A lazy sequence whose elements are formed by applying a given function to each element in one or more underlying lists. The function is applied lazily -- i.e., when you read a value from the list, C{LazyMap} will calculate that value by applying its function to the underlying lists' value(s). C{LazyMap} is essentially a lazy version of the Python primitive function C{map}. In particular, the following two expressions are equivalent: >>> map(f, sequences...) >>> list(LazyMap(f, sequences...)) Like the Python C{map} primitive, if the source lists do not have equal size, then the value C{None} will be supplied for the 'missing' elements. Lazy maps can be useful for conserving memory, in cases where individual values take up a lot of space. This is especially true if the underlying list's values are constructed lazily, as is the case with many corpus readers. A typical example of a use case for this class is performing feature detection on the tokens in a corpus. Since featuresets are encoded as dictionaries, which can take up a lot of memory, using a C{LazyMap} can significantly reduce memory usage when training and running classifiers. """ def __init__(self, function, *lists, **config): """ @param function: The function that should be applied to elements of C{lists}. It should take as many arguments as there are C{lists}. @param lists: The underlying lists. @kwparam cache_size: Determines the size of the cache used by this lazy map. (default=5) """ if not lists: raise TypeError('LazyMap requires at least two args') self._lists = lists self._func = function self._cache_size = config.get('cache_size', 5) if self._cache_size > 0: self._cache = {} else: self._cache = None # If you just take bool() of sum() here _all_lazy will be true just # in case n >= 1 list is an AbstractLazySequence. Presumably this # isn't what's intended. self._all_lazy = sum(isinstance(lst, AbstractLazySequence) for lst in lists) == len(lists) def iterate_from(self, index): # Special case: one lazy sublist if len(self._lists) == 1 and self._all_lazy: for value in self._lists[0].iterate_from(index): yield self._func(value) return # Special case: one non-lazy sublist elif len(self._lists) == 1: while True: try: yield self._func(self._lists[0][index]) except IndexError: return index += 1 # Special case: n lazy sublists elif self._all_lazy: iterators = [lst.iterate_from(index) for lst in self._lists] while True: elements = [] for iterator in iterators: try: elements.append(iterator.next()) except: elements.append(None) if elements == [None] * len(self._lists): return yield self._func(*elements) index += 1 # general case else: while True: try: elements = [lst[index] for lst in self._lists] except IndexError: elements = [None] * len(self._lists) for i, lst in enumerate(self._lists): try: elements[i] = lst[index] except IndexError: pass if elements == [None] * len(self._lists): return yield self._func(*elements) index += 1 def __getitem__(self, index): if isinstance(index, slice): sliced_lists = [lst[index] for lst in self._lists] return LazyMap(self._func, *sliced_lists) else: # Handle negative indices if index < 0: index += len(self) if index < 0: raise IndexError('index out of range') # Check the cache if self._cache is not None and index in self._cache: return self._cache[index] # Calculate the value try: val = self.iterate_from(index).next() except StopIteration: raise IndexError('index out of range') # Update the cache if self._cache is not None: if len(self._cache) > self._cache_size: self._cache.popitem() # discard random entry self._cache[index] = val # Return the value return val def __len__(self): return max(len(lst) for lst in self._lists) class LazyMappedList(Deprecated, LazyMap): """Use LazyMap instead.""" def __init__(self, lst, func): LazyMap.__init__(self, func, lst) class LazyZip(LazyMap): """ A lazy sequence whose elements are tuples, each containing the i-th element from each of the argument sequences. The returned list is truncated in length to the length of the shortest argument sequence. The tuples are constructed lazily -- i.e., when you read a value from the list, C{LazyZip} will calculate that value by forming a C{tuple} from the i-th element of each of the argument sequences. C{LazyZip} is essentially a lazy version of the Python primitive function C{zip}. In particular, the following two expressions are equivalent: >>> zip(sequences...) >>> list(LazyZip(sequences...)) Lazy zips can be useful for conserving memory in cases where the argument sequences are particularly long. A typical example of a use case for this class is combining long sequences of gold standard and predicted values in a classification or tagging task in order to calculate accuracy. By constructing tuples lazily and avoiding the creation of an additional long sequence, memory usage can be significantly reduced. """ def __init__(self, *lists): """ @param lists: the underlying lists @type lists: C{list} of C{list} """ LazyMap.__init__(self, lambda *elts: elts, *lists) def iterate_from(self, index): iterator = LazyMap.iterate_from(self, index) while index < len(self): yield iterator.next() index += 1 return def __len__(self): return min(len(lst) for lst in self._lists) class LazyEnumerate(LazyZip): """ A lazy sequence whose elements are tuples, each ontaining a count (from zero) and a value yielded by underlying sequence. C{LazyEnumerate} is useful for obtaining an indexed list. The tuples are constructed lazily -- i.e., when you read a value from the list, C{LazyEnumerate} will calculate that value by forming a C{tuple} from the count of the i-th element and the i-th element of the underlying sequence. C{LazyEnumerate} is essentially a lazy version of the Python primitive function C{enumerate}. In particular, the following two expressions are equivalent: >>> enumerate(sequence) >>> list(LazyEnumerate(sequence)) Lazy enumerations can be useful for conserving memory in cases where the argument sequences are particularly long. A typical example of a use case for this class is obtaining an indexed list for a long sequence of values. By constructing tuples lazily and avoiding the creation of an additional long sequence, memory usage can be significantly reduced. """ def __init__(self, lst): """ @param lst: the underlying list @type lst: C{list} """ LazyZip.__init__(self, xrange(len(lst)), lst) class LazyMappedChain(Deprecated, LazyConcatenation): """Use LazyConcatenation(LazyMap(func, lists)) instead.""" def __init__(self, lst, func): LazyConcatenation.__init__(self, LazyMap(func, lst)) ###################################################################### # Binary Search in a File ###################################################################### # inherited from pywordnet, by Oliver Steele def binary_search_file(file, key, cache={}, cacheDepth=-1): """ Searches through a sorted file using the binary search algorithm. @type file: file @param file: the file to be searched through. @type key: {string} @param key: the identifier we are searching for. @return: The line from the file with first word key. """ key = key + ' ' keylen = len(key) start = 0 currentDepth = 0 if hasattr(file, 'name'): end = os.stat(file.name).st_size - 1 else: file.seek(0, 2) end = file.tell() - 1 file.seek(0) while start < end: lastState = start, end middle = (start + end) / 2 if cache.get(middle): offset, line = cache[middle] else: line = "" while True: file.seek(max(0, middle - 1)) if middle > 0: file.readline() offset = file.tell() line = file.readline() if line != "": break # at EOF; try to find start of the last line middle = (start + middle)/2 if middle == end -1: return None if currentDepth < cacheDepth: cache[middle] = (offset, line) if offset > end: assert end != middle - 1, "infinite loop" end = middle - 1 elif line[:keylen] == key: return line elif line > key: assert end != middle - 1, "infinite loop" end = middle - 1 elif line < key: start = offset + len(line) - 1 currentDepth += 1 thisState = start, end if lastState == thisState: # Detects the condition where we're searching past the end # of the file, which is otherwise difficult to detect return None return None