# Natural Language Toolkit: Internal utility functions # # Copyright (C) 2001-2023 NLTK Project # Author: Steven Bird # Edward Loper # Nitin Madnani # URL: # For license information, see LICENSE.TXT import fnmatch import locale import os import re import stat import subprocess import sys import textwrap import types import warnings from xml.etree import ElementTree ########################################################################## # Java Via Command-Line ########################################################################## _java_bin = None _java_options = [] # [xx] add classpath option to config_java? def config_java(bin=None, options=None, verbose=False): """ Configure nltk's java interface, by letting nltk know where it can find the Java binary, and what extra options (if any) should be passed to Java when it is run. :param bin: The full path to the Java binary. If not specified, then nltk will search the system for a Java binary; and if one is not found, it will raise a ``LookupError`` exception. :type bin: str :param options: A list of options that should be passed to the Java binary when it is called. A common value is ``'-Xmx512m'``, which tells Java binary to increase the maximum heap size to 512 megabytes. If no options are specified, then do not modify the options list. :type options: list(str) """ global _java_bin, _java_options _java_bin = find_binary( "java", bin, env_vars=["JAVAHOME", "JAVA_HOME"], verbose=verbose, binary_names=["java.exe"], ) if options is not None: if isinstance(options, str): options = options.split() _java_options = list(options) def java(cmd, classpath=None, stdin=None, stdout=None, stderr=None, blocking=True): """ Execute the given java command, by opening a subprocess that calls Java. If java has not yet been configured, it will be configured by calling ``config_java()`` with no arguments. :param cmd: The java command that should be called, formatted as a list of strings. Typically, the first string will be the name of the java class; and the remaining strings will be arguments for that java class. :type cmd: list(str) :param classpath: A ``':'`` separated list of directories, JAR archives, and ZIP archives to search for class files. :type classpath: str :param stdin: Specify the executed program's standard input file handles, respectively. Valid values are ``subprocess.PIPE``, an existing file descriptor (a positive integer), an existing file object, 'pipe', 'stdout', 'devnull' and None. ``subprocess.PIPE`` indicates that a new pipe to the child should be created. With None, no redirection will occur; the child's file handles will be inherited from the parent. Additionally, stderr can be ``subprocess.STDOUT``, which indicates that the stderr data from the applications should be captured into the same file handle as for stdout. :param stdout: Specify the executed program's standard output file handle. See ``stdin`` for valid values. :param stderr: Specify the executed program's standard error file handle. See ``stdin`` for valid values. :param blocking: If ``false``, then return immediately after spawning the subprocess. In this case, the return value is the ``Popen`` object, and not a ``(stdout, stderr)`` tuple. :return: If ``blocking=True``, then return a tuple ``(stdout, stderr)``, containing the stdout and stderr outputs generated by the java command if the ``stdout`` and ``stderr`` parameters were set to ``subprocess.PIPE``; or None otherwise. If ``blocking=False``, then return a ``subprocess.Popen`` object. :raise OSError: If the java command returns a nonzero return code. """ subprocess_output_dict = { "pipe": subprocess.PIPE, "stdout": subprocess.STDOUT, "devnull": subprocess.DEVNULL, } stdin = subprocess_output_dict.get(stdin, stdin) stdout = subprocess_output_dict.get(stdout, stdout) stderr = subprocess_output_dict.get(stderr, stderr) if isinstance(cmd, str): raise TypeError("cmd should be a list of strings") # Make sure we know where a java binary is. if _java_bin is None: config_java() # Set up the classpath. if isinstance(classpath, str): classpaths = [classpath] else: classpaths = list(classpath) classpath = os.path.pathsep.join(classpaths) # Construct the full command string. cmd = list(cmd) cmd = ["-cp", classpath] + cmd cmd = [_java_bin] + _java_options + cmd # Call java via a subprocess p = subprocess.Popen(cmd, stdin=stdin, stdout=stdout, stderr=stderr) if not blocking: return p (stdout, stderr) = p.communicate() # Check the return code. if p.returncode != 0: print(_decode_stdoutdata(stderr)) raise OSError("Java command failed : " + str(cmd)) return (stdout, stderr) ###################################################################### # Parsing ###################################################################### class ReadError(ValueError): """ Exception raised by read_* functions when they fail. :param position: The index in the input string where an error occurred. :param expected: What was expected when an error occurred. """ def __init__(self, expected, position): ValueError.__init__(self, expected, position) self.expected = expected self.position = position def __str__(self): return f"Expected {self.expected} at {self.position}" _STRING_START_RE = re.compile(r"[uU]?[rR]?(\"\"\"|\'\'\'|\"|\')") def read_str(s, start_position): """ If a Python string literal begins at the specified position in the given string, then return a tuple ``(val, end_position)`` containing the value of the string literal and the position where it ends. Otherwise, raise a ``ReadError``. :param s: A string that will be checked to see if within which a Python string literal exists. :type s: str :param start_position: The specified beginning position of the string ``s`` to begin regex matching. :type start_position: int :return: A tuple containing the matched string literal evaluated as a string and the end position of the string literal. :rtype: tuple(str, int) :raise ReadError: If the ``_STRING_START_RE`` regex doesn't return a match in ``s`` at ``start_position``, i.e., open quote. If the ``_STRING_END_RE`` regex doesn't return a match in ``s`` at the end of the first match, i.e., close quote. :raise ValueError: If an invalid string (i.e., contains an invalid escape sequence) is passed into the ``eval``. :Example: >>> from nltk.internals import read_str >>> read_str('"Hello", World!', 0) ('Hello', 7) """ # Read the open quote, and any modifiers. m = _STRING_START_RE.match(s, start_position) if not m: raise ReadError("open quote", start_position) quotemark = m.group(1) # Find the close quote. _STRING_END_RE = re.compile(r"\\|%s" % quotemark) position = m.end() while True: match = _STRING_END_RE.search(s, position) if not match: raise ReadError("close quote", position) if match.group(0) == "\\": position = match.end() + 1 else: break # Process it, using eval. Strings with invalid escape sequences # might raise ValueError. try: return eval(s[start_position : match.end()]), match.end() except ValueError as e: raise ReadError("valid escape sequence", start_position) from e _READ_INT_RE = re.compile(r"-?\d+") def read_int(s, start_position): """ If an integer begins at the specified position in the given string, then return a tuple ``(val, end_position)`` containing the value of the integer and the position where it ends. Otherwise, raise a ``ReadError``. :param s: A string that will be checked to see if within which a Python integer exists. :type s: str :param start_position: The specified beginning position of the string ``s`` to begin regex matching. :type start_position: int :return: A tuple containing the matched integer casted to an int, and the end position of the int in ``s``. :rtype: tuple(int, int) :raise ReadError: If the ``_READ_INT_RE`` regex doesn't return a match in ``s`` at ``start_position``. :Example: >>> from nltk.internals import read_int >>> read_int('42 is the answer', 0) (42, 2) """ m = _READ_INT_RE.match(s, start_position) if not m: raise ReadError("integer", start_position) return int(m.group()), m.end() _READ_NUMBER_VALUE = re.compile(r"-?(\d*)([.]?\d*)?") def read_number(s, start_position): """ If an integer or float begins at the specified position in the given string, then return a tuple ``(val, end_position)`` containing the value of the number and the position where it ends. Otherwise, raise a ``ReadError``. :param s: A string that will be checked to see if within which a Python number exists. :type s: str :param start_position: The specified beginning position of the string ``s`` to begin regex matching. :type start_position: int :return: A tuple containing the matched number casted to a ``float``, and the end position of the number in ``s``. :rtype: tuple(float, int) :raise ReadError: If the ``_READ_NUMBER_VALUE`` regex doesn't return a match in ``s`` at ``start_position``. :Example: >>> from nltk.internals import read_number >>> read_number('Pi is 3.14159', 6) (3.14159, 13) """ m = _READ_NUMBER_VALUE.match(s, start_position) if not m or not (m.group(1) or m.group(2)): raise ReadError("number", start_position) if m.group(2): return float(m.group()), m.end() else: return int(m.group()), m.end() ###################################################################### # Check if a method has been overridden ###################################################################### def overridden(method): """ :return: True if ``method`` overrides some method with the same name in a base class. This is typically used when defining abstract base classes or interfaces, to allow subclasses to define either of two related methods: >>> class EaterI: ... '''Subclass must define eat() or batch_eat().''' ... def eat(self, food): ... if overridden(self.batch_eat): ... return self.batch_eat([food])[0] ... else: ... raise NotImplementedError() ... def batch_eat(self, foods): ... return [self.eat(food) for food in foods] :type method: instance method """ if isinstance(method, types.MethodType) and method.__self__.__class__ is not None: name = method.__name__ funcs = [ cls.__dict__[name] for cls in _mro(method.__self__.__class__) if name in cls.__dict__ ] return len(funcs) > 1 else: raise TypeError("Expected an instance method.") def _mro(cls): """ Return the method resolution order for ``cls`` -- i.e., a list containing ``cls`` and all its base classes, in the order in which they would be checked by ``getattr``. For new-style classes, this is just cls.__mro__. For classic classes, this can be obtained by a depth-first left-to-right traversal of ``__bases__``. """ if isinstance(cls, type): return cls.__mro__ else: mro = [cls] for base in cls.__bases__: mro.extend(_mro(base)) return mro ###################################################################### # Deprecation decorator & base class ###################################################################### # [xx] dedent msg first if it comes from a docstring. def _add_epytext_field(obj, field, message): """Add an epytext @field to a given object's docstring.""" indent = "" # If we already have a docstring, then add a blank line to separate # it from the new field, and check its indentation. if obj.__doc__: obj.__doc__ = obj.__doc__.rstrip() + "\n\n" indents = re.findall(r"(?<=\n)[ ]+(?!\s)", obj.__doc__.expandtabs()) if indents: indent = min(indents) # If we don't have a docstring, add an empty one. else: obj.__doc__ = "" obj.__doc__ += textwrap.fill( f"@{field}: {message}", initial_indent=indent, subsequent_indent=indent + " ", ) def deprecated(message): """ A decorator used to mark functions as deprecated. This will cause a warning to be printed the when the function is used. Usage: >>> from nltk.internals import deprecated >>> @deprecated('Use foo() instead') ... def bar(x): ... print(x/10) """ def decorator(func): msg = f"Function {func.__name__}() has been deprecated. {message}" msg = "\n" + textwrap.fill(msg, initial_indent=" ", subsequent_indent=" ") def newFunc(*args, **kwargs): warnings.warn(msg, category=DeprecationWarning, stacklevel=2) return func(*args, **kwargs) # Copy the old function's name, docstring, & dict newFunc.__dict__.update(func.__dict__) newFunc.__name__ = func.__name__ newFunc.__doc__ = func.__doc__ newFunc.__deprecated__ = True # Add a @deprecated field to the docstring. _add_epytext_field(newFunc, "deprecated", message) return newFunc return decorator class Deprecated: """ A base class used to mark deprecated classes. A typical usage is to alert users that the name of a class has changed: >>> from nltk.internals import Deprecated >>> class NewClassName: ... pass # All logic goes here. ... >>> class OldClassName(Deprecated, NewClassName): ... "Use NewClassName instead." The docstring of the deprecated class will be used in the deprecation warning message. """ def __new__(cls, *args, **kwargs): # Figure out which class is the deprecated one. dep_cls = None for base in _mro(cls): if Deprecated in base.__bases__: dep_cls = base break assert dep_cls, "Unable to determine which base is deprecated." # Construct an appropriate warning. doc = dep_cls.__doc__ or "".strip() # If there's a @deprecated field, strip off the field marker. doc = re.sub(r"\A\s*@deprecated:", r"", doc) # Strip off any indentation. doc = re.sub(r"(?m)^\s*", "", doc) # Construct a 'name' string. name = "Class %s" % dep_cls.__name__ if cls != dep_cls: name += " (base class for %s)" % cls.__name__ # Put it all together. msg = f"{name} has been deprecated. {doc}" # Wrap it. msg = "\n" + textwrap.fill(msg, initial_indent=" ", subsequent_indent=" ") warnings.warn(msg, category=DeprecationWarning, stacklevel=2) # Do the actual work of __new__. return object.__new__(cls) ########################################################################## # COUNTER, FOR UNIQUE NAMING ########################################################################## class Counter: """ A counter that auto-increments each time its value is read. """ def __init__(self, initial_value=0): self._value = initial_value def get(self): self._value += 1 return self._value ########################################################################## # Search for files/binaries ########################################################################## def find_file_iter( filename, env_vars=(), searchpath=(), file_names=None, url=None, verbose=False, finding_dir=False, ): """ Search for a file to be used by nltk. :param filename: The name or path of the file. :param env_vars: A list of environment variable names to check. :param file_names: A list of alternative file names to check. :param searchpath: List of directories to search. :param url: URL presented to user for download help. :param verbose: Whether or not to print path when a file is found. """ file_names = [filename] + (file_names or []) assert isinstance(filename, str) assert not isinstance(file_names, str) assert not isinstance(searchpath, str) if isinstance(env_vars, str): env_vars = env_vars.split() yielded = False # File exists, no magic for alternative in file_names: path_to_file = os.path.join(filename, alternative) if os.path.isfile(path_to_file): if verbose: print(f"[Found {filename}: {path_to_file}]") yielded = True yield path_to_file # Check the bare alternatives if os.path.isfile(alternative): if verbose: print(f"[Found {filename}: {alternative}]") yielded = True yield alternative # Check if the alternative is inside a 'file' directory path_to_file = os.path.join(filename, "file", alternative) if os.path.isfile(path_to_file): if verbose: print(f"[Found {filename}: {path_to_file}]") yielded = True yield path_to_file # Check environment variables for env_var in env_vars: if env_var in os.environ: if finding_dir: # This is to file a directory instead of file yielded = True yield os.environ[env_var] for env_dir in os.environ[env_var].split(os.pathsep): # Check if the environment variable contains a direct path to the bin if os.path.isfile(env_dir): if verbose: print(f"[Found {filename}: {env_dir}]") yielded = True yield env_dir # Check if the possible bin names exist inside the environment variable directories for alternative in file_names: path_to_file = os.path.join(env_dir, alternative) if os.path.isfile(path_to_file): if verbose: print(f"[Found {filename}: {path_to_file}]") yielded = True yield path_to_file # Check if the alternative is inside a 'file' directory # path_to_file = os.path.join(env_dir, 'file', alternative) # Check if the alternative is inside a 'bin' directory path_to_file = os.path.join(env_dir, "bin", alternative) if os.path.isfile(path_to_file): if verbose: print(f"[Found {filename}: {path_to_file}]") yielded = True yield path_to_file # Check the path list. for directory in searchpath: for alternative in file_names: path_to_file = os.path.join(directory, alternative) if os.path.isfile(path_to_file): yielded = True yield path_to_file # If we're on a POSIX system, then try using the 'which' command # to find the file. if os.name == "posix": for alternative in file_names: try: p = subprocess.Popen( ["which", alternative], stdout=subprocess.PIPE, stderr=subprocess.PIPE, ) stdout, stderr = p.communicate() path = _decode_stdoutdata(stdout).strip() if path.endswith(alternative) and os.path.exists(path): if verbose: print(f"[Found {filename}: {path}]") yielded = True yield path except (KeyboardInterrupt, SystemExit, OSError): raise finally: pass if not yielded: msg = ( "NLTK was unable to find the %s file!" "\nUse software specific " "configuration parameters" % filename ) if env_vars: msg += " or set the %s environment variable" % env_vars[0] msg += "." if searchpath: msg += "\n\n Searched in:" msg += "".join("\n - %s" % d for d in searchpath) if url: msg += f"\n\n For more information on {filename}, see:\n <{url}>" div = "=" * 75 raise LookupError(f"\n\n{div}\n{msg}\n{div}") def find_file( filename, env_vars=(), searchpath=(), file_names=None, url=None, verbose=False ): return next( find_file_iter(filename, env_vars, searchpath, file_names, url, verbose) ) def find_dir( filename, env_vars=(), searchpath=(), file_names=None, url=None, verbose=False ): return next( find_file_iter( filename, env_vars, searchpath, file_names, url, verbose, finding_dir=True ) ) def find_binary_iter( name, path_to_bin=None, env_vars=(), searchpath=(), binary_names=None, url=None, verbose=False, ): """ Search for a file to be used by nltk. :param name: The name or path of the file. :param path_to_bin: The user-supplied binary location (deprecated) :param env_vars: A list of environment variable names to check. :param file_names: A list of alternative file names to check. :param searchpath: List of directories to search. :param url: URL presented to user for download help. :param verbose: Whether or not to print path when a file is found. """ yield from find_file_iter( path_to_bin or name, env_vars, searchpath, binary_names, url, verbose ) def find_binary( name, path_to_bin=None, env_vars=(), searchpath=(), binary_names=None, url=None, verbose=False, ): return next( find_binary_iter( name, path_to_bin, env_vars, searchpath, binary_names, url, verbose ) ) def find_jar_iter( name_pattern, path_to_jar=None, env_vars=(), searchpath=(), url=None, verbose=False, is_regex=False, ): """ Search for a jar that is used by nltk. :param name_pattern: The name of the jar file :param path_to_jar: The user-supplied jar location, or None. :param env_vars: A list of environment variable names to check in addition to the CLASSPATH variable which is checked by default. :param searchpath: List of directories to search. :param is_regex: Whether name is a regular expression. """ assert isinstance(name_pattern, str) assert not isinstance(searchpath, str) if isinstance(env_vars, str): env_vars = env_vars.split() yielded = False # Make sure we check the CLASSPATH first env_vars = ["CLASSPATH"] + list(env_vars) # If an explicit location was given, then check it, and yield it if # it's present; otherwise, complain. if path_to_jar is not None: if os.path.isfile(path_to_jar): yielded = True yield path_to_jar else: raise LookupError( f"Could not find {name_pattern} jar file at {path_to_jar}" ) # Check environment variables for env_var in env_vars: if env_var in os.environ: if env_var == "CLASSPATH": classpath = os.environ["CLASSPATH"] for cp in classpath.split(os.path.pathsep): cp = os.path.expanduser(cp) if os.path.isfile(cp): filename = os.path.basename(cp) if ( is_regex and re.match(name_pattern, filename) or (not is_regex and filename == name_pattern) ): if verbose: print(f"[Found {name_pattern}: {cp}]") yielded = True yield cp # The case where user put directory containing the jar file in the classpath if os.path.isdir(cp): if not is_regex: if os.path.isfile(os.path.join(cp, name_pattern)): if verbose: print(f"[Found {name_pattern}: {cp}]") yielded = True yield os.path.join(cp, name_pattern) else: # Look for file using regular expression for file_name in os.listdir(cp): if re.match(name_pattern, file_name): if verbose: print( "[Found %s: %s]" % ( name_pattern, os.path.join(cp, file_name), ) ) yielded = True yield os.path.join(cp, file_name) else: jar_env = os.path.expanduser(os.environ[env_var]) jar_iter = ( ( os.path.join(jar_env, path_to_jar) for path_to_jar in os.listdir(jar_env) ) if os.path.isdir(jar_env) else (jar_env,) ) for path_to_jar in jar_iter: if os.path.isfile(path_to_jar): filename = os.path.basename(path_to_jar) if ( is_regex and re.match(name_pattern, filename) or (not is_regex and filename == name_pattern) ): if verbose: print(f"[Found {name_pattern}: {path_to_jar}]") yielded = True yield path_to_jar # Check the path list. for directory in searchpath: if is_regex: for filename in os.listdir(directory): path_to_jar = os.path.join(directory, filename) if os.path.isfile(path_to_jar): if re.match(name_pattern, filename): if verbose: print(f"[Found {filename}: {path_to_jar}]") yielded = True yield path_to_jar else: path_to_jar = os.path.join(directory, name_pattern) if os.path.isfile(path_to_jar): if verbose: print(f"[Found {name_pattern}: {path_to_jar}]") yielded = True yield path_to_jar if not yielded: # If nothing was found, raise an error msg = "NLTK was unable to find %s!" % name_pattern if env_vars: msg += " Set the %s environment variable" % env_vars[0] msg = textwrap.fill(msg + ".", initial_indent=" ", subsequent_indent=" ") if searchpath: msg += "\n\n Searched in:" msg += "".join("\n - %s" % d for d in searchpath) if url: msg += "\n\n For more information, on {}, see:\n <{}>".format( name_pattern, url, ) div = "=" * 75 raise LookupError(f"\n\n{div}\n{msg}\n{div}") def find_jar( name_pattern, path_to_jar=None, env_vars=(), searchpath=(), url=None, verbose=False, is_regex=False, ): return next( find_jar_iter( name_pattern, path_to_jar, env_vars, searchpath, url, verbose, is_regex ) ) def find_jars_within_path(path_to_jars): return [ os.path.join(root, filename) for root, dirnames, filenames in os.walk(path_to_jars) for filename in fnmatch.filter(filenames, "*.jar") ] def _decode_stdoutdata(stdoutdata): """Convert data read from stdout/stderr to unicode""" if not isinstance(stdoutdata, bytes): return stdoutdata encoding = getattr(sys.__stdout__, "encoding", locale.getpreferredencoding()) if encoding is None: return stdoutdata.decode() return stdoutdata.decode(encoding) ########################################################################## # Import Stdlib Module ########################################################################## def import_from_stdlib(module): """ When python is run from within the nltk/ directory tree, the current directory is included at the beginning of the search path. Unfortunately, that means that modules within nltk can sometimes shadow standard library modules. As an example, the stdlib 'inspect' module will attempt to import the stdlib 'tokenize' module, but will instead end up importing NLTK's 'tokenize' module instead (causing the import to fail). """ old_path = sys.path sys.path = [d for d in sys.path if d not in ("", ".")] m = __import__(module) sys.path = old_path return m ########################################################################## # Wrapper for ElementTree Elements ########################################################################## class ElementWrapper: """ A wrapper around ElementTree Element objects whose main purpose is to provide nicer __repr__ and __str__ methods. In addition, any of the wrapped Element's methods that return other Element objects are overridden to wrap those values before returning them. This makes Elements more convenient to work with in interactive sessions and doctests, at the expense of some efficiency. """ # Prevent double-wrapping: def __new__(cls, etree): """ Create and return a wrapper around a given Element object. If ``etree`` is an ``ElementWrapper``, then ``etree`` is returned as-is. """ if isinstance(etree, ElementWrapper): return etree else: return object.__new__(ElementWrapper) def __init__(self, etree): r""" Initialize a new Element wrapper for ``etree``. If ``etree`` is a string, then it will be converted to an Element object using ``ElementTree.fromstring()`` first: >>> ElementWrapper("") \n"> """ if isinstance(etree, str): etree = ElementTree.fromstring(etree) self.__dict__["_etree"] = etree def unwrap(self): """ Return the Element object wrapped by this wrapper. """ return self._etree ##//////////////////////////////////////////////////////////// # { String Representation ##//////////////////////////////////////////////////////////// def __repr__(self): s = ElementTree.tostring(self._etree, encoding="utf8").decode("utf8") if len(s) > 60: e = s.rfind("<") if (len(s) - e) > 30: e = -20 s = f"{s[:30]}...{s[e:]}" return "" % s def __str__(self): """ :return: the result of applying ``ElementTree.tostring()`` to the wrapped Element object. """ return ( ElementTree.tostring(self._etree, encoding="utf8").decode("utf8").rstrip() ) ##//////////////////////////////////////////////////////////// # { Element interface Delegation (pass-through) ##//////////////////////////////////////////////////////////// def __getattr__(self, attrib): return getattr(self._etree, attrib) def __setattr__(self, attr, value): return setattr(self._etree, attr, value) def __delattr__(self, attr): return delattr(self._etree, attr) def __setitem__(self, index, element): self._etree[index] = element def __delitem__(self, index): del self._etree[index] def __setslice__(self, start, stop, elements): self._etree[start:stop] = elements def __delslice__(self, start, stop): del self._etree[start:stop] def __len__(self): return len(self._etree) ##//////////////////////////////////////////////////////////// # { Element interface Delegation (wrap result) ##//////////////////////////////////////////////////////////// def __getitem__(self, index): return ElementWrapper(self._etree[index]) def __getslice__(self, start, stop): return [ElementWrapper(elt) for elt in self._etree[start:stop]] def getchildren(self): return [ElementWrapper(elt) for elt in self._etree] def getiterator(self, tag=None): return (ElementWrapper(elt) for elt in self._etree.getiterator(tag)) def makeelement(self, tag, attrib): return ElementWrapper(self._etree.makeelement(tag, attrib)) def find(self, path): elt = self._etree.find(path) if elt is None: return elt else: return ElementWrapper(elt) def findall(self, path): return [ElementWrapper(elt) for elt in self._etree.findall(path)] ###################################################################### # Helper for Handling Slicing ###################################################################### def slice_bounds(sequence, slice_obj, allow_step=False): """ Given a slice, return the corresponding (start, stop) bounds, taking into account None indices and negative indices. The following guarantees are made for the returned start and stop values: - 0 <= start <= len(sequence) - 0 <= stop <= len(sequence) - start <= stop :raise ValueError: If ``slice_obj.step`` is not None. :param allow_step: If true, then the slice object may have a non-None step. If it does, then return a tuple (start, stop, step). """ start, stop = (slice_obj.start, slice_obj.stop) # If allow_step is true, then include the step in our return # value tuple. if allow_step: step = slice_obj.step if step is None: step = 1 # Use a recursive call without allow_step to find the slice # bounds. If step is negative, then the roles of start and # stop (in terms of default values, etc), are swapped. if step < 0: start, stop = slice_bounds(sequence, slice(stop, start)) else: start, stop = slice_bounds(sequence, slice(start, stop)) return start, stop, step # Otherwise, make sure that no non-default step value is used. elif slice_obj.step not in (None, 1): raise ValueError( "slices with steps are not supported by %s" % sequence.__class__.__name__ ) # Supply default offsets. if start is None: start = 0 if stop is None: stop = len(sequence) # Handle negative indices. if start < 0: start = max(0, len(sequence) + start) if stop < 0: stop = max(0, len(sequence) + stop) # Make sure stop doesn't go past the end of the list. Note that # we avoid calculating len(sequence) if possible, because for lazy # sequences, calculating the length of a sequence can be expensive. if stop > 0: try: sequence[stop - 1] except IndexError: stop = len(sequence) # Make sure start isn't past stop. start = min(start, stop) # That's all folks! return start, stop ###################################################################### # Permission Checking ###################################################################### def is_writable(path): # Ensure that it exists. if not os.path.exists(path): return False # If we're on a posix system, check its permissions. if hasattr(os, "getuid"): statdata = os.stat(path) perm = stat.S_IMODE(statdata.st_mode) # is it world-writable? if perm & 0o002: return True # do we own it? elif statdata.st_uid == os.getuid() and (perm & 0o200): return True # are we in a group that can write to it? elif (statdata.st_gid in [os.getgid()] + os.getgroups()) and (perm & 0o020): return True # otherwise, we can't write to it. else: return False # Otherwise, we'll assume it's writable. # [xx] should we do other checks on other platforms? return True ###################################################################### # NLTK Error reporting ###################################################################### def raise_unorderable_types(ordering, a, b): raise TypeError( "unorderable types: %s() %s %s()" % (type(a).__name__, ordering, type(b).__name__) )