"""Run time libraries needed to run parsers generated by Yapps.
This module defines parse-time exception classes, a scanner class, a
base class for parsers produced by Yapps, and a context class that
keeps track of the parse stack.
"""
import sys, re
class SyntaxError(Exception):
"""When we run into an unexpected token, this is the exception to use"""
def __init__(self, charpos=-1, msg="Bad Token", context=None):
Exception.__init__(self)
self.charpos = charpos
self.msg = msg
self.context = context
def __str__(self):
if self.charpos < 0: return 'SyntaxError'
else: return 'SyntaxError@char%s(%s)' % (repr(self.charpos), self.msg)
class NoMoreTokens(Exception):
"""Another exception object, for when we run out of tokens"""
pass
class Scanner:
"""Yapps scanner.
The Yapps scanner can work in context sensitive or context
insensitive modes. The token(i) method is used to retrieve the
i-th token. It takes a restrict set that limits the set of tokens
it is allowed to return. In context sensitive mode, this restrict
set guides the scanner. In context insensitive mode, there is no
restriction (the set is always the full set of tokens).
"""
def __init__(self, patterns, ignore, input):
"""Initialize the scanner.
Parameters:
patterns : [(terminal, uncompiled regex), ...] or None
ignore : [terminal,...]
input : string
If patterns is None, we assume that the subclass has
defined self.patterns : [(terminal, compiled regex), ...].
Note that the patterns parameter expects uncompiled regexes,
whereas the self.patterns field expects compiled regexes.
"""
self.tokens = [] self.restrictions = []
self.input = input
self.pos = 0
self.ignore = ignore
self.first_line_number = 1
if patterns is not None:
self.patterns = []
for terminal, regex in patterns:
self.patterns.append( (terminal, re.compile(regex)) )
def get_token_pos(self):
"""Get the current token position in the input text."""
return len(self.tokens)
def get_char_pos(self):
"""Get the current char position in the input text."""
return self.pos
def get_prev_char_pos(self, i=None):
"""Get the previous position (one token back) in the input text."""
if self.pos == 0: return 0
if i is None: i = -1
return self.tokens[i][0]
def get_line_number(self):
"""Get the line number of the current position in the input text."""
return self.first_line_number + self.get_input_scanned().count('\n')
def get_column_number(self):
"""Get the column number of the current position in the input text."""
s = self.get_input_scanned()
i = s.rfind('\n') return len(s) - (i+1)
def get_input_scanned(self):
"""Get the portion of the input that has been tokenized."""
return self.input[:self.pos]
def get_input_unscanned(self):
"""Get the portion of the input that has not yet been tokenized."""
return self.input[self.pos:]
def token(self, i, restrict=None):
"""Get the i'th token in the input.
If i is one past the end, then scan for another token.
Args:
restrict : [token, ...] or None; if restrict is None, then any
token is allowed. You may call token(i) more than once.
However, the restrict set may never be larger than what was
passed in on the first call to token(i).
"""
if i == len(self.tokens):
self.scan(restrict)
if i < len(self.tokens):
if restrict and self.restrictions[i]:
for r in restrict:
if r not in self.restrictions[i]:
raise NotImplementedError("Unimplemented: restriction set changed")
return self.tokens[i]
raise NoMoreTokens()
def __repr__(self):
"""Print the last 10 tokens that have been scanned in"""
output = ''
for t in self.tokens[-10:]:
output = '%s\n (@%s) %s = %s' % (output,t[0],t[2],repr(t[3]))
return output
def scan(self, restrict):
"""Should scan another token and add it to the list, self.tokens,
and add the restriction to self.restrictions"""
while 1:
best_match = -1
best_pat = '(error)'
for p, regexp in self.patterns:
if restrict and p not in restrict and p not in self.ignore:
continue
m = regexp.match(self.input, self.pos)
if m and len(m.group(0)) > best_match:
best_pat = p
best_match = len(m.group(0))
if best_pat == '(error)' and best_match < 0:
msg = 'Bad Token'
if restrict:
msg = 'Trying to find one of '+', '.join(restrict)
raise SyntaxError(self.pos, msg)
if best_pat not in self.ignore:
token = (self.pos, self.pos+best_match, best_pat,
self.input[self.pos:self.pos+best_match])
self.pos = self.pos + best_match
if not self.tokens or token != self.tokens[-1]:
self.tokens.append(token)
self.restrictions.append(restrict)
return
else:
self.pos = self.pos + best_match
class Parser:
"""Base class for Yapps-generated parsers.
"""
def __init__(self, scanner):
self._scanner = scanner
self._pos = 0
def _peek(self, *types):
"""Returns the token type for lookahead; if there are any args
then the list of args is the set of token types to allow"""
tok = self._scanner.token(self._pos, types)
return tok[2]
def _scan(self, type):
"""Returns the matched text, and moves to the next token"""
tok = self._scanner.token(self._pos, [type])
if tok[2] != type:
raise SyntaxError(tok[0], 'Trying to find '+type+' :'+ ' ,'.join(self._scanner.restrictions[self._pos]))
self._pos = 1 + self._pos
return tok[3]
class Context:
"""Class to represent the parser's call stack.
Every rule creates a Context that links to its parent rule. The
contexts can be used for debugging.
"""
def __init__(self, parent, scanner, tokenpos, rule, args=()):
"""Create a new context.
Args:
parent: Context object or None
scanner: Scanner object
pos: integer (scanner token position)
rule: string (name of the rule)
args: tuple listing parameters to the rule
"""
self.parent = parent
self.scanner = scanner
self.tokenpos = tokenpos
self.rule = rule
self.args = args
def __str__(self):
output = ''
if self.parent: output = str(self.parent) + ' > '
output += self.rule
return output
def print_line_with_pointer(text, p):
"""Print the line of 'text' that includes position 'p',
along with a second line with a single caret (^) at position p"""
text = text[max(p-80, 0):p+80]
p = p - max(p-80, 0)
i = text[:p].rfind('\n')
j = text[:p].rfind('\r')
if i < 0 or (0 <= j < i): i = j
if 0 <= i < p:
p = p - i - 1
text = text[i+1:]
i = text.find('\n', p)
j = text.find('\r', p)
if i < 0 or (0 <= j < i): i = j
if i >= 0:
text = text[:i]
while len(text) > 70 and p > 60:
text = "..." + text[10:]
p = p - 7
print >>sys.stderr, '> ',text
print >>sys.stderr, '> ',' '*p + '^'
def print_error(input, err, scanner):
"""Print error messages, the parser stack, and the input text -- for human-readable error messages."""
line_number = scanner.get_line_number()
column_number = scanner.get_column_number()
print >>sys.stderr, '%d:%d: %s' % (line_number, column_number, err.msg)
context = err.context
if not context:
print_line_with_pointer(input, err.charpos)
while context:
print >>sys.stderr, 'while parsing %s%s:' % (context.rule, tuple(context.args))
print_line_with_pointer(input, context.scanner.get_prev_char_pos(context.tokenpos))
context = context.parent
def wrap_error_reporter(parser, rule):
try:
return getattr(parser, rule)()
except SyntaxError, e:
input = parser._scanner.input
print_error(input, e, parser._scanner)
except NoMoreTokens:
print >>sys.stderr, 'Could not complete parsing; stopped around here:'
print >>sys.stderr, parser._scanner
from twisted.xish.xpath import _Location, _AnyLocation, IndexValue, CompareValue, AttribValue, LiteralValue, Function
import sys, re
class XPathParserScanner(Scanner):
patterns = [
('"\\)"', re.compile('\\)')),
('","', re.compile(',')),
('"\\("', re.compile('\\(')),
('"@"', re.compile('@')),
('"\\]"', re.compile('\\]')),
('"\\["', re.compile('\\[')),
('"//"', re.compile('//')),
('"/"', re.compile('/')),
('\\s+', re.compile('\\s+')),
('INDEX', re.compile('[0-9]+')),
('WILDCARD', re.compile('\\*')),
('IDENTIFIER', re.compile('[a-zA-Z][a-zA-Z0-9_\\-]*')),
('ATTRIBUTE', re.compile('\\@[a-zA-Z][a-zA-Z0-9_\\-]*')),
('FUNCNAME', re.compile('[a-zA-Z][a-zA-Z0-9_]*')),
('CMP_EQ', re.compile('\\=')),
('CMP_NE', re.compile('\\!\\=')),
('STR_DQ', re.compile('"([^"]|(\\"))*?"')),
('STR_SQ', re.compile("'([^']|(\\'))*?'")),
('END', re.compile('$')),
]
def __init__(self, str):
Scanner.__init__(self,None,['\\s+'],str)
class XPathParser(Parser):
Context = Context
def XPATH(self, _parent=None):
_context = self.Context(_parent, self._scanner, self._pos, 'XPATH', [])
PATH = self.PATH(_context)
result = PATH; current = result
while self._peek('END', '"/"', '"//"') != 'END':
PATH = self.PATH(_context)
current.childLocation = PATH; current = current.childLocation
if self._peek() not in ['END', '"/"', '"//"']:
raise SyntaxError(charpos=self._scanner.get_prev_char_pos(), context=_context, msg='Need one of ' + ', '.join(['END', '"/"', '"//"']))
END = self._scan('END')
return result
def PATH(self, _parent=None):
_context = self.Context(_parent, self._scanner, self._pos, 'PATH', [])
_token = self._peek('"/"', '"//"')
if _token == '"/"':
self._scan('"/"')
result = _Location()
else: self._scan('"//"')
result = _AnyLocation()
_token = self._peek('IDENTIFIER', 'WILDCARD')
if _token == 'IDENTIFIER':
IDENTIFIER = self._scan('IDENTIFIER')
result.elementName = IDENTIFIER
else: WILDCARD = self._scan('WILDCARD')
result.elementName = None
while self._peek('"\\["', 'END', '"/"', '"//"') == '"\\["':
self._scan('"\\["')
PREDICATE = self.PREDICATE(_context)
result.predicates.append(PREDICATE)
self._scan('"\\]"')
if self._peek() not in ['"\\["', 'END', '"/"', '"//"']:
raise SyntaxError(charpos=self._scanner.get_prev_char_pos(), context=_context, msg='Need one of ' + ', '.join(['"\\["', 'END', '"/"', '"//"']))
return result
def PREDICATE(self, _parent=None):
_context = self.Context(_parent, self._scanner, self._pos, 'PREDICATE', [])
_token = self._peek('INDEX', '"@"', 'FUNCNAME', 'STR_DQ', 'STR_SQ')
if _token != 'INDEX':
EXPR = self.EXPR(_context)
return EXPR
else: INDEX = self._scan('INDEX')
return IndexValue(INDEX)
def EXPR(self, _parent=None):
_context = self.Context(_parent, self._scanner, self._pos, 'EXPR', [])
VALUE = self.VALUE(_context)
e = VALUE
if self._peek('CMP_EQ', 'CMP_NE', '"\\]"') != '"\\]"':
CMP = self.CMP(_context)
VALUE = self.VALUE(_context)
e = CompareValue(e, CMP, VALUE)
return e
def VALUE(self, _parent=None):
_context = self.Context(_parent, self._scanner, self._pos, 'VALUE', [])
_token = self._peek('"@"', 'FUNCNAME', 'STR_DQ', 'STR_SQ')
if _token == '"@"':
self._scan('"@"')
IDENTIFIER = self._scan('IDENTIFIER')
return AttribValue(IDENTIFIER)
elif _token == 'FUNCNAME':
FUNCNAME = self._scan('FUNCNAME')
f = Function(FUNCNAME); args = []
self._scan('"\\("')
if self._peek('"\\)"', '"@"', 'FUNCNAME', '","', 'STR_DQ', 'STR_SQ') not in ['"\\)"', '","']:
VALUE = self.VALUE(_context)
args.append(VALUE)
while self._peek('","', '"\\)"') == '","':
self._scan('","')
VALUE = self.VALUE(_context)
args.append(VALUE)
if self._peek() not in ['","', '"\\)"']:
raise SyntaxError(charpos=self._scanner.get_prev_char_pos(), context=_context, msg='Need one of ' + ', '.join(['","', '"\\)"']))
self._scan('"\\)"')
f.setParams(*args); return f
else: STR = self.STR(_context)
return LiteralValue(STR[1:len(STR)-1])
def CMP(self, _parent=None):
_context = self.Context(_parent, self._scanner, self._pos, 'CMP', [])
_token = self._peek('CMP_EQ', 'CMP_NE')
if _token == 'CMP_EQ':
CMP_EQ = self._scan('CMP_EQ')
return CMP_EQ
else: CMP_NE = self._scan('CMP_NE')
return CMP_NE
def STR(self, _parent=None):
_context = self.Context(_parent, self._scanner, self._pos, 'STR', [])
_token = self._peek('STR_DQ', 'STR_SQ')
if _token == 'STR_DQ':
STR_DQ = self._scan('STR_DQ')
return STR_DQ
else: STR_SQ = self._scan('STR_SQ')
return STR_SQ
def parse(rule, text):
P = XPathParser(XPathParserScanner(text))
return wrap_error_reporter(P, rule)
if __name__ == '__main__':
from sys import argv, stdin
if len(argv) >= 2:
if len(argv) >= 3:
f = open(argv[2],'r')
else:
f = stdin
print parse(argv[1], f.read())
else: print >>sys.stderr, 'Args: <rule> [<filename>]'