mirror of
https://github.com/python/cpython.git
synced 2025-10-31 05:31:20 +00:00
204 lines
8 KiB
Python
204 lines
8 KiB
Python
# Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.
|
|
# Licensed to PSF under a Contributor Agreement.
|
|
|
|
"""Parser engine for the grammar tables generated by pgen.
|
|
|
|
The grammar table must be loaded first.
|
|
|
|
See Parser/parser.c in the Python distribution for additional info on
|
|
how this parsing engine works.
|
|
|
|
"""
|
|
|
|
# Local imports
|
|
from . import token
|
|
|
|
class ParseError(Exception):
|
|
"""Exception to signal the parser is stuck."""
|
|
|
|
def __init__(self, msg, type, value, context):
|
|
Exception.__init__(self, "%s: type=%r, value=%r, context=%r" %
|
|
(msg, type, value, context))
|
|
self.msg = msg
|
|
self.type = type
|
|
self.value = value
|
|
self.context = context
|
|
|
|
def __reduce__(self):
|
|
return type(self), (self.msg, self.type, self.value, self.context)
|
|
|
|
class Parser(object):
|
|
"""Parser engine.
|
|
|
|
The proper usage sequence is:
|
|
|
|
p = Parser(grammar, [converter]) # create instance
|
|
p.setup([start]) # prepare for parsing
|
|
<for each input token>:
|
|
if p.addtoken(...): # parse a token; may raise ParseError
|
|
break
|
|
root = p.rootnode # root of abstract syntax tree
|
|
|
|
A Parser instance may be reused by calling setup() repeatedly.
|
|
|
|
A Parser instance contains state pertaining to the current token
|
|
sequence, and should not be used concurrently by different threads
|
|
to parse separate token sequences.
|
|
|
|
See driver.py for how to get input tokens by tokenizing a file or
|
|
string.
|
|
|
|
Parsing is complete when addtoken() returns True; the root of the
|
|
abstract syntax tree can then be retrieved from the rootnode
|
|
instance variable. When a syntax error occurs, addtoken() raises
|
|
the ParseError exception. There is no error recovery; the parser
|
|
cannot be used after a syntax error was reported (but it can be
|
|
reinitialized by calling setup()).
|
|
|
|
"""
|
|
|
|
def __init__(self, grammar, convert=None):
|
|
"""Constructor.
|
|
|
|
The grammar argument is a grammar.Grammar instance; see the
|
|
grammar module for more information.
|
|
|
|
The parser is not ready yet for parsing; you must call the
|
|
setup() method to get it started.
|
|
|
|
The optional convert argument is a function mapping concrete
|
|
syntax tree nodes to abstract syntax tree nodes. If not
|
|
given, no conversion is done and the syntax tree produced is
|
|
the concrete syntax tree. If given, it must be a function of
|
|
two arguments, the first being the grammar (a grammar.Grammar
|
|
instance), and the second being the concrete syntax tree node
|
|
to be converted. The syntax tree is converted from the bottom
|
|
up.
|
|
|
|
A concrete syntax tree node is a (type, value, context, nodes)
|
|
tuple, where type is the node type (a token or symbol number),
|
|
value is None for symbols and a string for tokens, context is
|
|
None or an opaque value used for error reporting (typically a
|
|
(lineno, offset) pair), and nodes is a list of children for
|
|
symbols, and None for tokens.
|
|
|
|
An abstract syntax tree node may be anything; this is entirely
|
|
up to the converter function.
|
|
|
|
"""
|
|
self.grammar = grammar
|
|
self.convert = convert or (lambda grammar, node: node)
|
|
|
|
def setup(self, start=None):
|
|
"""Prepare for parsing.
|
|
|
|
This *must* be called before starting to parse.
|
|
|
|
The optional argument is an alternative start symbol; it
|
|
defaults to the grammar's start symbol.
|
|
|
|
You can use a Parser instance to parse any number of programs;
|
|
each time you call setup() the parser is reset to an initial
|
|
state determined by the (implicit or explicit) start symbol.
|
|
|
|
"""
|
|
if start is None:
|
|
start = self.grammar.start
|
|
# Each stack entry is a tuple: (dfa, state, node).
|
|
# A node is a tuple: (type, value, context, children),
|
|
# where children is a list of nodes or None, and context may be None.
|
|
newnode = (start, None, None, [])
|
|
stackentry = (self.grammar.dfas[start], 0, newnode)
|
|
self.stack = [stackentry]
|
|
self.rootnode = None
|
|
self.used_names = set() # Aliased to self.rootnode.used_names in pop()
|
|
|
|
def addtoken(self, type, value, context):
|
|
"""Add a token; return True iff this is the end of the program."""
|
|
# Map from token to label
|
|
ilabel = self.classify(type, value, context)
|
|
# Loop until the token is shifted; may raise exceptions
|
|
while True:
|
|
dfa, state, node = self.stack[-1]
|
|
states, first = dfa
|
|
arcs = states[state]
|
|
# Look for a state with this label
|
|
for i, newstate in arcs:
|
|
t, v = self.grammar.labels[i]
|
|
if ilabel == i:
|
|
# Look it up in the list of labels
|
|
assert t < 256
|
|
# Shift a token; we're done with it
|
|
self.shift(type, value, newstate, context)
|
|
# Pop while we are in an accept-only state
|
|
state = newstate
|
|
while states[state] == [(0, state)]:
|
|
self.pop()
|
|
if not self.stack:
|
|
# Done parsing!
|
|
return True
|
|
dfa, state, node = self.stack[-1]
|
|
states, first = dfa
|
|
# Done with this token
|
|
return False
|
|
elif t >= 256:
|
|
# See if it's a symbol and if we're in its first set
|
|
itsdfa = self.grammar.dfas[t]
|
|
itsstates, itsfirst = itsdfa
|
|
if ilabel in itsfirst:
|
|
# Push a symbol
|
|
self.push(t, self.grammar.dfas[t], newstate, context)
|
|
break # To continue the outer while loop
|
|
else:
|
|
if (0, state) in arcs:
|
|
# An accepting state, pop it and try something else
|
|
self.pop()
|
|
if not self.stack:
|
|
# Done parsing, but another token is input
|
|
raise ParseError("too much input",
|
|
type, value, context)
|
|
else:
|
|
# No success finding a transition
|
|
raise ParseError("bad input", type, value, context)
|
|
|
|
def classify(self, type, value, context):
|
|
"""Turn a token into a label. (Internal)"""
|
|
if type == token.NAME:
|
|
# Keep a listing of all used names
|
|
self.used_names.add(value)
|
|
# Check for reserved words
|
|
ilabel = self.grammar.keywords.get(value)
|
|
if ilabel is not None:
|
|
return ilabel
|
|
ilabel = self.grammar.tokens.get(type)
|
|
if ilabel is None:
|
|
raise ParseError("bad token", type, value, context)
|
|
return ilabel
|
|
|
|
def shift(self, type, value, newstate, context):
|
|
"""Shift a token. (Internal)"""
|
|
dfa, state, node = self.stack[-1]
|
|
newnode = (type, value, context, None)
|
|
newnode = self.convert(self.grammar, newnode)
|
|
if newnode is not None:
|
|
node[-1].append(newnode)
|
|
self.stack[-1] = (dfa, newstate, node)
|
|
|
|
def push(self, type, newdfa, newstate, context):
|
|
"""Push a nonterminal. (Internal)"""
|
|
dfa, state, node = self.stack[-1]
|
|
newnode = (type, None, context, [])
|
|
self.stack[-1] = (dfa, newstate, node)
|
|
self.stack.append((newdfa, 0, newnode))
|
|
|
|
def pop(self):
|
|
"""Pop a nonterminal. (Internal)"""
|
|
popdfa, popstate, popnode = self.stack.pop()
|
|
newnode = self.convert(self.grammar, popnode)
|
|
if newnode is not None:
|
|
if self.stack:
|
|
dfa, state, node = self.stack[-1]
|
|
node[-1].append(newnode)
|
|
else:
|
|
self.rootnode = newnode
|
|
self.rootnode.used_names = self.used_names
|