lex.py.wml
No OneTemporary
Actions

Subscribers

None

File Metadata

Created: Sat, Nov 2, 06:17

lex.py.wml
View Options

	<protect>#-----------------------------------------------------------------------------
	# ply: lex.py
	#
	# Author: David M. Beazley (beazley@cs.uchicago.edu)
	# Department of Computer Science
	# University of Chicago
	# Chicago, IL 60637
	#
	# Copyright (C) 2001, David M. Beazley
	#
	# $Header$
	#
	# This library is free software; you can redistribute it and/or
	# modify it under the terms of the GNU Lesser General Public
	# License as published by the Free Software Foundation; either
	# version 2.1 of the License, or (at your option) any later version.
	#
	# This library is distributed in the hope that it will be useful,
	# but WITHOUT ANY WARRANTY; without even the implied warranty of
	# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	# Lesser General Public License for more details.
	#
	# You should have received a copy of the GNU Lesser General Public
	# License along with this library; if not, write to the Free Software
	# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	#
	# See the file COPYING for a complete copy of the LGPL.
	#
	#
	# This module automatically constructs a lexical analysis module from regular
	# expression rules defined in a user-defined module. The idea is essentially the same
	# as that used in John Aycock's Spark framework, but the implementation works
	# at the module level rather than requiring the use of classes.
	#
	# This module tries to provide an interface that is closely modeled after
	# the traditional lex interface in Unix. It also differs from Spark
	# in that:
	#
	# - It provides more extensive error checking and reporting if
	# the user supplies a set of regular expressions that can't
	# be compiled or if there is any other kind of a problem in
	# the specification.
	#
	# - The interface is geared towards LALR(1) and LR(1) parser
	# generators. That is tokens are generated one at a time
	# rather than being generated in advanced all in one step.
	#
	# There are a few limitations of this module
	#
	# - The module interface makes it somewhat awkward to support more
	# than one lexer at a time. Although somewhat inelegant from a
	# design perspective, this is rarely a practical concern for
	# most compiler projects.
	#
	# - The lexer requires that the entire input text be read into
	# a string before scanning. I suppose that most machines have
	# enough memory to make this a minor issues, but it makes
	# the lexer somewhat difficult to use in interactive sessions
	# or with streaming data.
	#
	#-----------------------------------------------------------------------------

	r"""
	lex.py

	This module builds lex-like scanners based on regular expression rules.
	To use the module, simply write a collection of regular expression rules
	and actions like this:

	# lexer.py
	import lex

	# Define a list of valid tokens
	tokens = (
	'IDENTIFIER', 'NUMBER', 'PLUS', 'MINUS'
	)

	# Define tokens as functions
	def t_IDENTIFIER(t):
	r' ([a-zA-Z_](\w\|_)* '
	return t

	def t_NUMBER(t):
	r' \d+ '
	return t

	# Some simple tokens with no actions
	t_PLUS = r'\+'
	t_MINUS = r'-'

	# Initialize the lexer
	lex.lex()

	The tokens list is required and contains a complete list of all valid
	token types that the lexer is allowed to produce. Token types are
	restricted to be valid identifiers. This means that 'MINUS' is a valid
	token type whereas '-' is not.

	Rules are defined by writing a function with a name of the form
	t_rulename. Each rule must accept a single argument which is
	a token object generated by the lexer. This token has the following
	attributes:

	t.type = type string of the token. This is initially set to the
	name of the rule without the leading t_
	t.value = The value of the lexeme.
	t.lineno = The value of the line number where the token was encountered

	For example, the t_NUMBER() rule above might be called with the following:

	t.type = 'NUMBER'
	t.value = '42'
	t.lineno = 3

	Each rule returns the token object it would like to supply to the
	parser. In most cases, the token t is returned with few, if any
	modifications. To discard a token for things like whitespace or
	comments, simply return nothing. For instance:

	def t_whitespace(t):
	r' \s+ '
	pass

	For faster lexing, you can also define this in terms of the ignore set like this:

	t_ignore = ' \t'

	The characters in this string are ignored by the lexer. Use of this feature can speed
	up parsing significantly since scanning will immediately proceed to the next token.

	lex requires that the token returned by each rule has an attribute
	t.type. Other than this, rules are free to return any kind of token
	object that they wish and may construct a new type of token object
	from the attributes of t (provided the new object has the required
	type attribute).

	If illegal characters are encountered, the scanner executes the
	function t_error(t) where t is a token representing the rest of the
	string that hasn't been matched. If this function isn't defined, a
	LexError exception is raised. The .text attribute of this exception
	object contains the part of the string that wasn't matched.

	The t.skip(n) method can be used to skip ahead n characters in the
	input stream. This is usually only used in the error handling rule.
	For instance, the following rule would print an error message and
	continue:

	def t_error(t):
	print "Illegal character in input %s" % t.value[0]
	t.skip(1)

	Of course, a nice scanner might wish to skip more than one character
	if the input looks very corrupted.

	The lex module defines a t.lineno attribute on each token that can be used
	to track the current line number in the input. The value of this
	variable is not modified by lex so it is up to your lexer module
	to correctly update its value depending on the lexical properties
	of the input language. To do this, you might write rules such as
	the following:

	def t_newline(t):
	r' \n+ '
	t.lineno += t.value.count("\n")

	To initialize your lexer so that it can be used, simply call the lex.lex()
	function in your rule file. If there are any errors in your
	specification, warning messages or an exception will be generated to
	alert you to the problem.

	(dave: this needs to be rewritten)
	To use the newly constructed lexer from another module, simply do
	this:

	import lex
	import lexer
	plex.input("position = initial + rate*60")

	while 1:
	token = plex.token() # Get a token
	if not token: break # No more tokens
	... do whatever ...

	Assuming that the module 'lexer' has initialized plex as shown
	above, parsing modules can safely import 'plex' without having
	to import the rule file or any additional imformation about the
	scanner you have defined.
	"""

	# -----------------------------------------------------------------------------


	__version__ = "1.4"

	import re, types, sys, copy

	# Exception thrown when invalid token encountered and no default
	class LexError(Exception):
	def __init__(self,message,s):
	self.args = (message,)
	self.text = s

	# Token class
	class LexToken:
	def __str__(self):
	return "LexToken(%s,%r,%d)" % (self.type,self.value,self.lineno)
	def __repr__(self):
	return str(self)
	def skip(self,n):
	try:
	self._skipn += n
	except AttributeError:
	self._skipn = n

	# -----------------------------------------------------------------------------
	# Lexer class
	#
	# input() - Store a new string in the lexer
	# token() - Get the next token
	# -----------------------------------------------------------------------------

	class Lexer:
	def __init__(self):
	self.lexre = None # Master regular expression
	self.lexdata = None # Actual input data (as a string)
	self.lexpos = 0 # Current position in input text
	self.lexlen = 0 # Length of the input text
	self.lexindexfunc = [ ] # Reverse mapping of groups to functions and types
	self.lexerrorf = None # Error rule (if any)
	self.lextokens = None # List of valid tokens
	self.lexignore = None # Ignored characters
	self.lineno = 1 # Current line number
	self.debug = 0 # Debugging mode
	self.optimize = 0 # Optimized mode
	self.token = self.errtoken

	def __copy__(self):
	c = Lexer()
	c.lexre = self.lexre
	c.lexdata = self.lexdata
	c.lexpos = self.lexpos
	c.lexlen = self.lexlen
	c.lenindexfunc = self.lexindexfunc
	c.lexerrorf = self.lexerrorf
	c.lextokens = self.lextokens
	c.lexignore = self.lexignore
	c.lineno = self.lineno
	c.optimize = self.optimize
	c.token = c.realtoken

	# ------------------------------------------------------------
	# input() - Push a new string into the lexer
	# ------------------------------------------------------------
	def input(self,s):
	if not isinstance(s,types.StringType):
	raise ValueError, "Expected a string"
	self.lexdata = s
	self.lexpos = 0
	self.lexlen = len(s)
	self.token = self.realtoken

	# Change the token routine to point to realtoken()
	global token
	if token == self.errtoken:
	token = self.token

	# ------------------------------------------------------------
	# errtoken() - Return error if token is called with no data
	# ------------------------------------------------------------
	def errtoken(self):
	raise RuntimeError, "No input string given with input()"

	# ------------------------------------------------------------
	# token() - Return the next token from the Lexer
	#
	# Note: This function has been carefully implemented to be as fast
	# as possible. Don't make changes unless you really know what
	# you are doing
	# ------------------------------------------------------------
	def realtoken(self):
	# Make local copies of frequently referenced attributes
	lexpos = self.lexpos
	lexlen = self.lexlen
	lexignore = self.lexignore
	lexdata = self.lexdata

	while lexpos < lexlen:
	# This code provides some short-circuit code for whitespace, tabs, and other ignored characters
	if lexdata[lexpos] in lexignore:
	lexpos += 1
	continue

	# Look for a regular expression match
	m = self.lexre.match(lexdata,lexpos)
	if m:
	i = m.lastindex
	lexpos = m.end()
	tok = LexToken()
	tok.value = m.group()
	tok.lineno = self.lineno
	tok.lexer = self
	func,tok.type = self.lexindexfunc[i]
	if not func:
	self.lexpos = lexpos
	return tok

	# If token is processed by a function, call it
	self.lexpos = lexpos
	newtok = func(tok)
	self.lineno = tok.lineno # Update line number

	# Every function must return a token, if nothing, we just move to next token
	if not newtok: continue

	# Verify type of the token. If not in the token map, raise an error
	if not self.optimize:
	if not self.lextokens.has_key(newtok.type):
	raise LexError, ("%s:%d: Rule '%s' returned an unknown token type '%s'" % (
	func.func_code.co_filename, func.func_code.co_firstlineno,
	func.__name__, newtok.type),lexdata[lexpos:])

	return newtok

	# No match. Call t_error() if defined.
	if self.lexerrorf:
	tok = LexToken()
	tok.value = self.lexdata[lexpos:]
	tok.lineno = self.lineno
	tok.type = "error"
	tok.lexer = self
	oldpos = lexpos
	newtok = self.lexerrorf(tok)
	lexpos += getattr(tok,"_skipn",0)
	if oldpos == lexpos:
	# Error method didn't change text position at all. This is an error.
	self.lexpos = lexpos
	raise LexError, ("Scanning error. Illegal character '%s'" % (lexdata[lexpos]), lexdata[lexpos:])
	if not newtok: continue
	self.lexpos = lexpos
	return newtok

	self.lexpos = lexpos
	raise LexError, ("No match found", lexdata[lexpos:])

	# No more input data
	self.lexpos = lexpos + 1
	return None


	# -----------------------------------------------------------------------------
	# validate_file()
	#
	# This checks to see if there are duplicated t_rulename() functions or strings
	# in the parser input file. This is done using a simple regular expression
	# match on each line in the filename.
	# -----------------------------------------------------------------------------

	def validate_file(filename):
	import os.path
	base,ext = os.path.splitext(filename)
	if ext != '.py': return 1 # No idea what the file is. Return OK

	try:
	f = open(filename)
	lines = f.readlines()
	f.close()
	except IOError:
	return 1 # Oh well

	fre = re.compile(r'\sdef\s+(t_[a-zA-Z_0-9])\(')
	sre = re.compile(r'\s(t_[a-zA-Z_0-9])\s*=')
	counthash = { }
	linen = 1
	noerror = 1
	for l in lines:
	m = fre.match(l)
	if not m:
	m = sre.match(l)
	if m:
	name = m.group(1)
	prev = counthash.get(name)
	if not prev:
	counthash[name] = linen
	else:
	print "%s:%d: Rule %s redefined. Previously defined on line %d" % (filename,linen,name,prev)
	noerror = 0
	linen += 1
	return noerror

	# -----------------------------------------------------------------------------
	# _read_lextab(module)
	#
	# Reads lexer table from a lextab file instead of using introspection.
	# -----------------------------------------------------------------------------

	def _read_lextab(lexer, fdict, module):
	exec "import %s as lextab" % module
	lexer.lexre = re.compile(lextab._lexre, re.VERBOSE)
	lexer.lexindexfunc = lextab._lextab
	for i in range(len(lextab._lextab)):
	t = lexer.lexindexfunc[i]
	if t:
	if t[0]:
	lexer.lexindexfunc[i] = (fdict[t[0]],t[1])
	lexer.lextokens = lextab._lextokens
	lexer.lexignore = lextab._lexignore
	if lextab._lexerrorf:
	lexer.lexerrorf = fdict[lextab._lexerrorf]

	# -----------------------------------------------------------------------------
	# lex(module)
	#
	# Build all of the regular expression rules from definitions in the supplied module
	# -----------------------------------------------------------------------------
	def lex(module=None,debug=0,optimize=0,lextab="lextab"):
	ldict = None
	regex = ""
	error = 0
	files = { }
	lexer = Lexer()
	lexer.debug = debug
	lexer.optimize = optimize
	global token,input

	if module:
	# User supplied a module object.
	if isinstance(module, types.ModuleType):
	ldict = module.__dict__
	elif isinstance(module, types.InstanceType):
	_items = [(k,getattr(module,k)) for k in dir(module)]
	ldict = { }
	for (i,v) in _items:
	ldict[i] = v
	else:
	raise ValueError,"Expected a module or instance"

	else:
	# No module given. We might be able to get information from the caller.
	try:
	raise RuntimeError
	except RuntimeError:
	e,b,t = sys.exc_info()
	f = t.tb_frame
	f = f.f_back # Walk out to our calling function
	ldict = f.f_globals # Grab its globals dictionary

	if optimize and lextab:
	try:
	_read_lextab(lexer,ldict, lextab)
	if not lexer.lexignore: lexer.lexignore = ""
	token = lexer.token
	input = lexer.input
	return lexer

	except ImportError:
	pass

	# Get the tokens map
	if (module and isinstance(module,types.InstanceType)):
	tokens = getattr(module,"tokens",None)
	else:
	try:
	tokens = ldict["tokens"]
	except KeyError:
	tokens = None

	if not tokens:
	raise SyntaxError,"lex: module does not define 'tokens'"
	if not (isinstance(tokens,types.ListType) or isinstance(tokens,types.TupleType)):
	raise SyntaxError,"lex: tokens must be a list or tuple."

	# Build a dictionary of valid token names
	lexer.lextokens = { }
	if not optimize:

	# Utility function for verifying tokens
	def is_identifier(s):
	for c in s:
	if not (c.isalnum() or c == '_'): return 0
	return 1

	for n in tokens:
	if not is_identifier(n):
	print "lex: Bad token name '%s'" % n
	error = 1
	if lexer.lextokens.has_key(n):
	print "lex: Warning. Token '%s' multiply defined." % n
	lexer.lextokens[n] = None
	else:
	for n in tokens: lexer.lextokens[n] = None


	if debug:
	print "lex: tokens = '%s'" % lexer.lextokens.keys()

	# Get a list of symbols with the t_ prefix
	tsymbols = [f for f in ldict.keys() if f[:2] == 't_']

	# Now build up a list of functions and a list of strings
	fsymbols = [ ]
	ssymbols = [ ]
	for f in tsymbols:
	if callable(ldict[f]):
	fsymbols.append(ldict[f])
	elif isinstance(ldict[f], types.StringType):
	ssymbols.append((f,ldict[f]))
	else:
	print "lex: %s not defined as a function or string" % f
	error = 1

	# Sort the functions by line number
	fsymbols.sort(lambda x,y: cmp(x.func_code.co_firstlineno,y.func_code.co_firstlineno))

	# Sort the strings by regular expression length
	ssymbols.sort(lambda x,y: (len(x[1]) < len(y[1])) - (len(x[1]) > len(y[1])))

	# Check for non-empty symbols
	if len(fsymbols) == 0 and len(ssymbols) == 0:
	raise SyntaxError,"lex: no rules of the form t_rulename are defined."

	# Add all of the rules defined with actions first
	for f in fsymbols:

	line = f.func_code.co_firstlineno
	file = f.func_code.co_filename
	files[file] = None

	ismethod = isinstance(f, types.MethodType)

	if not optimize:
	nargs = f.func_code.co_argcount
	if ismethod:
	reqargs = 2
	else:
	reqargs = 1
	if nargs > reqargs:
	print "%s:%d: Rule '%s' has too many arguments." % (file,line,f.__name__)
	error = 1
	continue

	if nargs < reqargs:
	print "%s:%d: Rule '%s' requires an argument." % (file,line,f.__name__)
	error = 1
	continue

	if f.__name__ == 't_ignore':
	print "%s:%d: Rule '%s' must be defined as a string." % (file,line,f.__name__)
	error = 1
	continue

	if f.__name__ == 't_error':
	lexer.lexerrorf = f
	continue

	if f.__doc__:
	if not optimize:
	try:
	c = re.compile(f.__doc__, re.VERBOSE)
	except re.error,e:
	print "%s:%d: Invalid regular expression for rule '%s'. %s" % (file,line,f.__name__,e)
	error = 1
	continue

	if debug:
	print "lex: Adding rule %s -> '%s'" % (f.__name__,f.__doc__)

	# Okay. The regular expression seemed okay. Let's append it to the master regular
	# expression we're building

	if (regex): regex += "\|"
	regex += "(?P<%s>%s)" % (f.__name__,f.__doc__)
	else:
	print "%s:%d: No regular expression defined for rule '%s'" % (file,line,f.__name__)

	# Now add all of the simple rules
	for name,r in ssymbols:

	if name == 't_ignore':
	lexer.lexignore = r
	continue

	if not optimize:
	if name == 't_error':
	raise SyntaxError,"lex: Rule 't_error' must be defined as a function"
	error = 1
	continue

	if not lexer.lextokens.has_key(name[2:]):
	print "lex: Rule '%s' defined for an unspecified token %s." % (name,name[2:])
	error = 1
	continue
	try:
	c = re.compile(r,re.VERBOSE)
	except re.error,e:
	print "lex: Invalid regular expression for rule '%s'. %s" % (name,e)
	error = 1
	continue
	if debug:
	print "lex: Adding rule %s -> '%s'" % (name,r)

	if regex: regex += "\|"
	regex += "(?P<%s>%s)" % (name,r)

	if not optimize:
	for f in files.keys():
	if not validate_file(f):
	error = 1
	try:
	if debug:
	print "lex: regex = '%s'" % regex
	lexer.lexre = re.compile(regex, re.VERBOSE)

	# Build the index to function map for the matching engine
	lexer.lexindexfunc = [ None ] * (max(lexer.lexre.groupindex.values())+1)
	for f,i in lexer.lexre.groupindex.items():
	handle = ldict[f]
	if type(handle) in (types.FunctionType, types.MethodType):
	lexer.lexindexfunc[i] = (handle,handle.__name__[2:])
	else:
	# If rule was specified as a string, we build an anonymous
	# callback function to carry out the action
	lexer.lexindexfunc[i] = (None,f[2:])

	# If a lextab was specified, we create a file containing the precomputed
	# regular expression and index table

	if lextab and optimize:
	lt = open(lextab+".py","w")
	lt.write("# %s.py. This file automatically created by PLY. Don't edit.\n" % lextab)
	lt.write("_lexre = %s\n" % repr(regex))
	lt.write("_lextab = [\n");
	for i in range(0,len(lexer.lexindexfunc)):
	t = lexer.lexindexfunc[i]
	if t:
	if t[0]:
	lt.write(" ('%s',%s),\n"% (t[0].__name__, repr(t[1])))
	else:
	lt.write(" (None,%s),\n" % repr(t[1]))
	else:
	lt.write(" None,\n")

	lt.write("]\n");
	lt.write("_lextokens = %s\n" % repr(lexer.lextokens))
	lt.write("_lexignore = %s\n" % repr(lexer.lexignore))
	if (lexer.lexerrorf):
	lt.write("_lexerrorf = %s\n" % repr(lexer.lexerrorf.__name__))
	else:
	lt.write("_lexerrorf = None\n")
	lt.close()

	except re.error,e:
	print "lex: Fatal error. Unable to compile regular expression rules. %s" % e
	error = 1
	if error:
	raise SyntaxError,"lex: Unable to build lexer."
	if not lexer.lexerrorf:
	print "lex: Warning. no t_error rule is defined."

	if not lexer.lexignore: lexer.lexignore = ""

	# Create global versions of the token() and input() functions
	token = lexer.token
	input = lexer.input

	return lexer

	# -----------------------------------------------------------------------------
	# run()
	#
	# This runs the lexer as a main program
	# -----------------------------------------------------------------------------

	def runmain(lexer=None,data=None):
	if not data:
	try:
	filename = sys.argv[1]
	f = open(filename)
	data = f.read()
	f.close()
	except IndexError:
	print "Reading from standard input (type EOF to end):"
	data = sys.stdin.read()

	if lexer:
	_input = lexer.input
	else:
	_input = input
	_input(data)
	if lexer:
	_token = lexer.token
	else:
	_token = token

	while 1:
	tok = _token()
	if not tok: break
	print "(%s,'%s',%d)" % (tok.type, tok.value, tok.lineno)




	</protect>

lex.py.wmlNo OneTemporaryActions

File Metadata

lex.py.wmlView Options

Event Timeline

lex.py.wml
No OneTemporary
Actions

lex.py.wml
View Options