cpython/Lib/compiler/transformer.py

# Copyright 1997-1998 Greg Stein and Bill Tutt
#
# transformer.py -- transforms Python parse trees
#
# Takes an input parse tree and transforms it into a higher-level parse
# tree that is a bit more amenable to code generation. Essentially, it
# simply introduces some additional semantics.
#
# Written by Greg Stein (gstein@lyra.org)
#        and Bill Tutt (rassilon@lima.mudlib.org)
# February 1997.
#
# Support for Node subclasses written by
#  Jeremy Hylton (jeremy@cnri.reston.va.us)
#
# The output tree has the following nodes:
#
# Source Python line #'s appear at the end of each of all of these nodes
# If a line # doesn't apply, there will be a None instead.
#
# module:     doc, node
# stmt:       [ node1, ..., nodeN ]
# function:   name, argnames, defaults, flags, doc, codeNode
# lambda:     argnames, defaults, flags, codeNode
# classdef:   name, bases, doc, codeNode
# pass:
# break:
# continue:
# for:        assignNode, listNode, bodyNode, elseNode
# while:      testNode, bodyNode, elseNode
# if:         [ (testNode, suiteNode), ... ], elseNode
# exec:       expr1Node, expr2Node, expr3Node
# from:       modname, [ name1, ..., nameN ]
# import:     [ name1, ..., nameN ]
# raise:      expr1Node, expr2Node, expr3Node
# tryfinally: trySuiteNode, finSuiteNode
# tryexcept:  trySuiteNode, [ (exprNode, assgnNode, suiteNode), ... ], elseNode
# return:     valueNode
# const:      value
# print:      [ node1, ..., nodeN ]
# printnl:    [ node1, ..., nodeN ]
# discard:    exprNode
# assign:     [ node1, ..., nodeN ], exprNode
# ass_tuple:  [ node1, ..., nodeN ]
# ass_list:   [ node1, ..., nodeN ]
# ass_name:   name, flags
# ass_attr:   exprNode, attrname, flags
# list:       [ node1, ..., nodeN ]
# dict:       [ (key1, val1), ..., (keyN, valN) ]
# not:        exprNode
# compare:    exprNode, [ (op, node), ..., (op, node) ]
# name:       name
# global:     [ name1, ..., nameN ]
# backquote:  node
# getattr:    exprNode, attrname
# call_func:  node, [ arg1, ..., argN ]
# keyword:    name, exprNode
# subscript:  exprNode, flags, [ sub1, ..., subN ]
# ellipsis:
# sliceobj:   [ node1, ..., nodeN ]
# slice:      exprNode, flags, lowerNode, upperNode
# assert:     expr1, expr2
#
# Compiled as "binary" ops:
# tuple:      [ node1, ..., nodeN ]
# or:         [ node1, ..., nodeN ]
# and:        [ node1, ..., nodeN ]
# bitor:      [ node1, ..., nodeN ]
# bitxor:     [ node1, ..., nodeN ]
# bitand:     [ node1, ..., nodeN ]
#
# Operations easily evaluateable on constants:
# <<:         exprNode, shiftNode
# >>:         exprNode, shiftNode
# +:          leftNode, rightNode
# -:          leftNode, rightNode
# *:          leftNode, rightNode
# /:          leftNode, rightNode
# %:          leftNode, rightNode
# power:      leftNode, rightNode
# unary+:     node
# unary-:     node
# invert:     node
#

"""Parse tree transformation module.

Exposes the Transformer class with a number of methods for returning a
"cleansed AST" instead of the parse tree that the parser exposes.
"""

import ast
import parser
import symbol
import token
import string

import pprint

error = 'walker.error'

from consts import CO_VARARGS, CO_VARKEYWORDS
from consts import OP_ASSIGN, OP_DELETE, OP_APPLY

def asList(nodes):
  l = []
  for item in nodes:
    if hasattr(item, "asList"):
      l.append(item.asList())
    else:
      if type(item) is type( (None, None) ):
        l.append(tuple(asList(item)))
      elif type(item) is type( [] ):
        l.append(asList(item))
      else:
        l.append(item)
  return l

def Node(*args):
  kind = args[0]
  if ast.nodes.has_key(kind):
    try:
      return apply(ast.nodes[kind], args[1:])
    except TypeError:
      print ast.nodes[kind], len(args), args
      raise
  else:
    raise error, "Can't find appropriate Node type."
    #return apply(ast.Node, args)

class Transformer:
  """Utility object for transforming Python parse trees.

  Exposes the following methods:
    tree = transform(ast_tree)
    tree = parsesuite(text)
    tree = parseexpr(text)
    tree = parsefile(fileob | filename)
  """

  def __init__(self):
    self._dispatch = { }
    for value, name in symbol.sym_name.items():
      if hasattr(self, name):
        self._dispatch[value] = getattr(self, name)

  def transform(self, tree):
    """Transform an AST into a modified parse tree."""
    if type(tree) != type(()) and type(tree) != type([]):
      tree = parser.ast2tuple(tree,1)
    return self.compile_node(tree)

  def parsesuite(self, text):
    """Return a modified parse tree for the given suite text."""
    # Hack for handling non-native line endings on non-DOS like OSs.
    text = string.replace(text, '\x0d', '')
    return self.transform(parser.suite(text))

  def parseexpr(self, text):
    """Return a modified parse tree for the given expression text."""
    return self.transform(parser.expr(text))

  def parsefile(self, file):
    """Return a modified parse tree for the contents of the given file."""
    if type(file) == type(''):
      file = open(file)
    return self.parsesuite(file.read())

  # --------------------------------------------------------------
  #
  # PRIVATE METHODS
  #

  def compile_node(self, node):
    ### emit a line-number node?
    n = node[0]
    if n == symbol.single_input:
      return self.single_input(node[1:])
    if n == symbol.file_input:
      return self.file_input(node[1:])
    if n == symbol.eval_input:
      return self.eval_input(node[1:])
    if n == symbol.lambdef:
      return self.lambdef(node[1:])
    if n == symbol.funcdef:
      return self.funcdef(node[1:])
    if n == symbol.classdef:
      return self.classdef(node[1:])

    raise error, ('unexpected node type', n)

  def single_input(self, node):
    ### do we want to do anything about being "interactive" ?

    # NEWLINE | simple_stmt | compound_stmt NEWLINE
    n = node[0][0]
    if n != token.NEWLINE:
      return self.com_stmt(node[0])

    return Node('pass')

  def file_input(self, nodelist):
    doc = self.get_docstring(nodelist, symbol.file_input)
    stmts = [ ]
    for node in nodelist:
      if node[0] != token.ENDMARKER and node[0] != token.NEWLINE:
        self.com_append_stmt(stmts, node)
    return Node('module', doc, Node('stmt', stmts))

  def eval_input(self, nodelist):
    # from the built-in function input()
    ### is this sufficient?
    return self.com_node(nodelist[0])

  def funcdef(self, nodelist):
    # funcdef: 'def' NAME parameters ':' suite
    # parameters: '(' [varargslist] ')'

    lineno = nodelist[1][2]
    name   = nodelist[1][1]
    args   = nodelist[2][2]

    if args[0] == symbol.varargslist:
      names, defaults, flags = self.com_arglist(args[1:])
    else:
      names = defaults = ()
      flags = 0
    doc = self.get_docstring(nodelist[4])

    # code for function
    code = self.com_node(nodelist[4])

    n = Node('function', name, names, defaults, flags, doc, code)
    n.lineno = lineno
    return n

  def lambdef(self, nodelist):
    # lambdef: 'lambda' [varargslist] ':' test
    if nodelist[2][0] == symbol.varargslist:
      names, defaults, flags = self.com_arglist(nodelist[2][1:])
    else:
      names = defaults = ()
      flags = 0

    # code for lambda
    code = self.com_node(nodelist[-1])

    n = Node('lambda', names, defaults, flags, code)
    n.lineno = nodelist[1][2]
    return n

  def classdef(self, nodelist):
    # classdef: 'class' NAME ['(' testlist ')'] ':' suite

    name = nodelist[1][1]
    doc = self.get_docstring(nodelist[-1])
    if nodelist[2][0] == token.COLON:
      bases = []
    else:
      bases = self.com_bases(nodelist[3])

    # code for class
    code = self.com_node(nodelist[-1])

    n = Node('classdef', name, bases, doc, code)
    n.lineno = nodelist[1][2]
    return n

  def stmt(self, nodelist):
    return self.com_stmt(nodelist[0])

  small_stmt = stmt
  flow_stmt = stmt
  compound_stmt = stmt

  def simple_stmt(self, nodelist):
    # small_stmt (';' small_stmt)* [';'] NEWLINE
    stmts = [ ]
    for i in range(0, len(nodelist), 2):
      self.com_append_stmt(stmts, nodelist[i])
    return Node('stmt', stmts)

  def parameters(self, nodelist):
    raise error

  def varargslist(self, nodelist):
    raise error

  def fpdef(self, nodelist):
    raise error

  def fplist(self, nodelist):
    raise error

  def dotted_name(self, nodelist):
    raise error

  def comp_op(self, nodelist):
    raise error

  def trailer(self, nodelist):
    raise error

  def sliceop(self, nodelist):
    raise error

  def argument(self, nodelist):
    raise error

  # --------------------------------------------------------------
  #
  # STATEMENT NODES  (invoked by com_node())
  #

  def expr_stmt(self, nodelist):
    # testlist ('=' testlist)*
    exprNode = self.com_node(nodelist[-1])
    if len(nodelist) == 1:
      return Node('discard', exprNode)
    nodes = [ ]
    for i in range(0, len(nodelist) - 2, 2):
      nodes.append(self.com_assign(nodelist[i], OP_ASSIGN))
    n = Node('assign', nodes, exprNode)
    n.lineno = nodelist[1][2]
    return n

  def print_stmt(self, nodelist):
    # print: (test ',')* [test]
    items = [ ]
    for i in range(1, len(nodelist), 2):
      items.append(self.com_node(nodelist[i]))
    if nodelist[-1][0] == token.COMMA:
      n = Node('print', items)
      n.lineno = nodelist[0][2]
      return n
    n = Node('printnl', items)
    n.lineno = nodelist[0][2]
    return n

  def del_stmt(self, nodelist):
    return self.com_assign(nodelist[1], OP_DELETE)

  def pass_stmt(self, nodelist):
    # pass:
    n = Node('pass')
    n.lineno = nodelist[0][2]
    return n

  def break_stmt(self, nodelist):
    # break:
    n = Node('break')
    n.lineno = nodelist[0][2]
    return n

  def continue_stmt(self, nodelist):
    # continue
    n = Node('continue')
    n.lineno = nodelist[0][2]
    return n

  def return_stmt(self, nodelist):
    # return: [testlist]
    if len(nodelist) < 2:
      n = Node('return', Node('const', None))
      n.lineno = nodelist[0][2]
      return n
    n = Node('return', self.com_node(nodelist[1]))
    n.lineno = nodelist[0][2]
    return n

  def raise_stmt(self, nodelist):
    # raise: [test [',' test [',' test]]]
    if len(nodelist) > 5:
      expr3 = self.com_node(nodelist[5])
    else:
      expr3 = None
    if len(nodelist) > 3:
      expr2 = self.com_node(nodelist[3])
    else:
      expr2 = None
    if len(nodelist) > 1:
      expr1 = self.com_node(nodelist[1])
    else:
      expr1 = None
    n = Node('raise', expr1, expr2, expr3)
    n.lineno = nodelist[0][2]
    return n

  def import_stmt(self, nodelist):
    # import: dotted_name (',' dotted_name)* |
    # from: dotted_name 'import' ('*' | NAME (',' NAME)*)
    names = [ ]
    if nodelist[0][1][0] == 'f':
      for i in range(3, len(nodelist), 2):
        # note: nodelist[i] could be (token.STAR, '*') or (token.NAME, name)
        names.append(nodelist[i][1])
      n = Node('from', self.com_dotted_name(nodelist[1]), names)
      n.lineno = nodelist[0][2]
      return n

    for i in range(1, len(nodelist), 2):
      names.append(self.com_dotted_name(nodelist[i]))
    n = Node('import', names)
    n.lineno = nodelist[0][2]
    return n

  def global_stmt(self, nodelist):
    # global: NAME (',' NAME)*
    names = [ ]
    for i in range(1, len(nodelist), 2):
      names.append(nodelist[i][1])
    n = Node('global', names)
    n.lineno = nodelist[0][2]
    return n

  def exec_stmt(self, nodelist):
    # exec_stmt: 'exec' expr ['in' expr [',' expr]]
    expr1 = self.com_node(nodelist[1])
    if len(nodelist) >= 4:
      expr2 = self.com_node(nodelist[3])
      if len(nodelist) >= 6:
        expr3 = self.com_node(nodelist[5])
      else:
        expr3 = None
    else:
      expr2 = expr3 = None

    n = Node('exec', expr1, expr2, expr3)
    n.lineno = nodelist[0][2]
    return n

  def assert_stmt(self, nodelist):
    # 'assert': test, [',' test]
    expr1 = self.com_node(nodelist[1])
    if (len(nodelist) == 4):
      expr2 = self.com_node(nodelist[3])
    else:
      expr2 = Node('name', 'None')
    n = Node('assert', expr1, expr2)
    n.lineno = nodelist[0][2]
    return n

  def if_stmt(self, nodelist):
    # if: test ':' suite ('elif' test ':' suite)* ['else' ':' suite]
    tests = [ ]
    for i in range(0, len(nodelist) - 3, 4):
      testNode = self.com_node(nodelist[i + 1])
      suiteNode = self.com_node(nodelist[i + 3])
      tests.append((testNode, suiteNode))

    if len(nodelist) % 4 == 3:
      elseNode = self.com_node(nodelist[-1])
##      elseNode.lineno = nodelist[-1][1][2]
    else:
      elseNode = None
    n = Node('if', tests, elseNode)
    n.lineno = nodelist[0][2]
    return n

  def while_stmt(self, nodelist):
    # 'while' test ':' suite ['else' ':' suite]

    testNode = self.com_node(nodelist[1])
    bodyNode = self.com_node(nodelist[3])

    if len(nodelist) > 4:
      elseNode = self.com_node(nodelist[6])
    else:
      elseNode = None

    n = Node('while', testNode, bodyNode, elseNode)
    n.lineno = nodelist[0][2]
    return n

  def for_stmt(self, nodelist):
    # 'for' exprlist 'in' exprlist ':' suite ['else' ':' suite]

    assignNode = self.com_assign(nodelist[1], OP_ASSIGN)
    listNode = self.com_node(nodelist[3])
    bodyNode = self.com_node(nodelist[5])

    if len(nodelist) > 8:
      elseNode = self.com_node(nodelist[8])
    else:
      elseNode = None

    n = Node('for', assignNode, listNode, bodyNode, elseNode)
    n.lineno = nodelist[0][2]
    return n

  def try_stmt(self, nodelist):
    # 'try' ':' suite (except_clause ':' suite)+ ['else' ':' suite]
    # | 'try' ':' suite 'finally' ':' suite
    if nodelist[3][0] != symbol.except_clause:
      return self.com_try_finally(nodelist)

    return self.com_try_except(nodelist)

  def suite(self, nodelist):
    # simple_stmt | NEWLINE INDENT NEWLINE* (stmt NEWLINE*)+ DEDENT
    if len(nodelist) == 1:
      return self.com_stmt(nodelist[0])

    stmts = [ ]
    for node in nodelist:
      if node[0] == symbol.stmt:
        self.com_append_stmt(stmts, node)
    return Node('stmt', stmts)

  # --------------------------------------------------------------
  #
  # EXPRESSION NODES  (invoked by com_node())
  #

  def testlist(self, nodelist):
    # testlist: expr (',' expr)* [',']
    # exprlist: expr (',' expr)* [',']
    return self.com_binary('tuple', nodelist)

  exprlist = testlist

  def test(self, nodelist):
    # and_test ('or' and_test)* | lambdef
    if len(nodelist) == 1 and nodelist[0][0] == symbol.lambdef:
      return self.lambdef(nodelist[0])
    return self.com_binary('or', nodelist)

  def and_test(self, nodelist):
    # not_test ('and' not_test)*
    return self.com_binary('and', nodelist)

  def not_test(self, nodelist):
    # 'not' not_test | comparison
    result = self.com_node(nodelist[-1])
    if len(nodelist) == 2:
      n = Node('not', result)
      n.lineno = nodelist[0][2]
      return n
    return result

  def comparison(self, nodelist):
    # comparison: expr (comp_op expr)*
    node = self.com_node(nodelist[0])
    if len(nodelist) == 1:
      return node

    results = [ ]
    for i in range(2, len(nodelist), 2):
      nl = nodelist[i-1]

      # comp_op: '<' | '>' | '=' | '>=' | '<=' | '<>' | '!=' | '=='
      #          | 'in' | 'not' 'in' | 'is' | 'is' 'not'
      n = nl[1]
      if n[0] == token.NAME:
        type = n[1]
        if len(nl) == 3:
          if type == 'not':
            type = 'not in'
          else:
            type = 'is not'
      else:
        type = _cmp_types[n[0]]

      lineno = nl[1][2]
      results.append(type, self.com_node(nodelist[i]))

    # we need a special "compare" node so that we can distinguish
    #   3 < x < 5   from    (3 < x) < 5
    # the two have very different semantics and results (note that the
    # latter form is always true)

    n = Node('compare', node, results)
    n.lineno = lineno
    return n

  def expr(self, nodelist):
    # xor_expr ('|' xor_expr)*
    return self.com_binary('bitor', nodelist)

  def xor_expr(self, nodelist):
    # xor_expr ('^' xor_expr)*
    return self.com_binary('bitxor', nodelist)

  def and_expr(self, nodelist):
    # xor_expr ('&' xor_expr)*
    return self.com_binary('bitand', nodelist)

  def shift_expr(self, nodelist):
    # shift_expr ('<<'|'>>' shift_expr)*
    node = self.com_node(nodelist[0])
    for i in range(2, len(nodelist), 2):
      right = self.com_node(nodelist[i])
      if nodelist[i-1][0] == token.LEFTSHIFT:
        node = Node('<<', [node, right])
        node.lineno = nodelist[1][2]
      else:
        node = Node('>>', [node, right])
        node.lineno = nodelist[1][2]
    return node

  def arith_expr(self, nodelist):
    node = self.com_node(nodelist[0])
    for i in range(2, len(nodelist), 2):
      right = self.com_node(nodelist[i])
      if nodelist[i-1][0] == token.PLUS:
        node = Node('+', [node, right])
        node.lineno = nodelist[1][2]
      else:
        node = Node('-', [node, right])
        node.lineno = nodelist[1][2]
    return node

  def term(self, nodelist):
    node = self.com_node(nodelist[0])
    for i in range(2, len(nodelist), 2):
      right = self.com_node(nodelist[i])
      if nodelist[i-1][0] == token.STAR:
        node = Node('*', [node, right])
        node.lineno = nodelist[1][2]
      elif nodelist[i-1][0] == token.SLASH:
        node = Node('/', [node, right])
        node.lineno = nodelist[1][2]
      else:
        node = Node('%', [node, right])
        node.lineno = nodelist[1][2]
    return node

  def factor(self, nodelist):
    t = nodelist[0][0]
    node = self.com_node(nodelist[-1])
    if t == token.PLUS:
      node = Node('unary+', node)
      node.lineno = nodelist[0][2]
    elif t == token.MINUS:
      node = Node('unary-', node)
      node.lineno = nodelist[0][2]
    elif t == token.TILDE:
      node = Node('invert', node)
      node.lineno = nodelist[0][2]
    return node

  def power(self, nodelist):
    # power: atom trailer* ('**' factor)*
    node = self.com_node(nodelist[0])
    for i in range(1, len(nodelist)):
      if nodelist[i][0] == token.DOUBLESTAR:
        n = Node('power', [node, self.com_node(nodelist[i+1])])
        n.lineno = nodelist[i][2]
        return n

      node = self.com_apply_trailer(node, nodelist[i])

    return node

  def atom(self, nodelist):
    t = nodelist[0][0]
    if t == token.LPAR:
      if nodelist[1][0] == token.RPAR:
        n = Node('const', ())
        n.lineno = nodelist[0][2]
        return n
      return self.com_node(nodelist[1])

    if t == token.LSQB:
      if nodelist[1][0] == token.RSQB:
        n = Node('const', [ ])
        n.lineno = nodelist[0][2]
        return n
      return self.com_list_constructor(nodelist[1])

    if t == token.LBRACE:
      if nodelist[1][0] == token.RBRACE:
        return Node('const', { })
      return self.com_dictmaker(nodelist[1])

    if t == token.BACKQUOTE:
      n = Node('backquote', self.com_node(nodelist[1]))
      n.lineno = nodelist[0][2]
      return n

    if t == token.NUMBER:
      ### need to verify this matches compile.c
      k = eval(nodelist[0][1])
      n = Node('const', k)
      n.lineno = nodelist[0][2]
      return n

    if t == token.STRING:
      ### need to verify this matches compile.c
      k = ''
      for node in nodelist:
        k = k + eval(node[1])
      n = Node('const', k)
      n.lineno = nodelist[0][2]
      return n

    if t == token.NAME:
      ### any processing to do?
      n = Node('name', nodelist[0][1])
      n.lineno = nodelist[0][2]
      return n

    raise error, "unknown node type"

  # --------------------------------------------------------------
  #
  # INTERNAL PARSING UTILITIES
  #

  def com_node(self, node):
    # Note: compile.c has handling in com_node for del_stmt, pass_stmt,
    #       break_stmt, stmt, small_stmt, flow_stmt, simple_stmt,
    #       and compound_stmt.
    #       We'll just dispatch them.

    #
    # A ';' at the end of a line can make a NEWLINE token appear here,
    # Render it harmless. (genc discards ('discard', ('const', xxxx)) Nodes)
    # 
    if node[0] == token.NEWLINE:
      return Node('discard', Node('const', None))

    if node[0] not in _legal_node_types:
      raise error, 'illegal node passed to com_node: %s' % node[0]

    return self._dispatch[node[0]](node[1:])

  def com_arglist(self, nodelist):
    # varargslist:
    #   (fpdef ['=' test] ',')* ('*' NAME [',' ('**'|'*' '*') NAME]
    #  | fpdef ['=' test] (',' fpdef ['=' test])* [',']
    #  | ('**'|'*' '*') NAME)
    # fpdef: NAME | '(' fplist ')'
    # fplist: fpdef (',' fpdef)* [',']
    names = [ ]
    defaults = [ ]
    flags = 0

    i = 0
    while i < len(nodelist):
      node = nodelist[i]
      if node[0] == token.STAR or node[0] == token.DOUBLESTAR:
        if node[0] == token.STAR:
          node = nodelist[i+1]
          if node[0] == token.NAME:
            names.append(node[1])
            flags = flags | CO_VARARGS
            i = i + 3

        if i < len(nodelist):
          # should be DOUBLESTAR or STAR STAR
          if nodelist[i][0] == token.DOUBLESTAR:
            node = nodelist[i+1]
          else:
            node = nodelist[i+2]
          names.append(node[1])
          flags = flags | CO_VARKEYWORDS

        break

      # fpdef: NAME | '(' fplist ')'
      names.append(self.com_fpdef(node))

      i = i + 1
      if i >= len(nodelist):
        break

      if nodelist[i][0] == token.EQUAL:
        defaults.append(self.com_node(nodelist[i + 1]))
        i = i + 2
      elif len(defaults):
        # Treat "(a=1, b)" as "(a=1, b=None)"
        defaults.append(Node('const', None))

      i = i + 1

    return names, defaults, flags

  def com_fpdef(self, node):
    # fpdef: NAME | '(' fplist ')'
    if node[1][0] == token.LPAR:
      return self.com_fplist(node[2])
    return node[1][1]

  def com_fplist(self, node):
    # fplist: fpdef (',' fpdef)* [','] 
    if len(node) == 2:
      return self.com_fpdef(node[1])
    list = [ ]
    for i in range(1, len(node), 2):
      list.append(self.com_fpdef(node[i]))
    return tuple(list)

  def com_dotted_name(self, node):
    # String together the dotted names and return the string
    name = ""
    for n in node:
      if type(n) == type(()) and n[0] == 1:
        name = name + n[1] + '.'
    return name[:-1]

  def com_bases(self, node):
    bases = [ ]
    for i in range(1, len(node), 2):
      bases.append(self.com_node(node[i]))
    return bases

  def com_try_finally(self, nodelist):
    # try_fin_stmt: "try" ":" suite "finally" ":" suite
    n = Node('tryfinally', self.com_node(nodelist[2]), self.com_node(nodelist[5]))
    n.lineno = nodelist[0][2]
    return n

  def com_try_except(self, nodelist):
    # try_except: 'try' ':' suite (except_clause ':' suite)* ['else' suite]
    #tryexcept:  [TryNode, [except_clauses], elseNode)]
    stmt = self.com_node(nodelist[2])
    clauses = []
    elseNode = None
    for i in range(3, len(nodelist), 3):
      node = nodelist[i]
      if node[0] == symbol.except_clause:
        # except_clause: 'except' [expr [',' expr]] */
        if len(node) > 2:
          expr1 = self.com_node(node[2])
          if len(node) > 4:
            expr2 = self.com_assign(node[4], OP_ASSIGN)
          else:
            expr2 = None
        else:
          expr1 = expr2 = None
        clauses.append(expr1, expr2, self.com_node(nodelist[i+2]))

      if node[0] == token.NAME:
        elseNode = self.com_node(nodelist[i+2])
    n = Node('tryexcept', self.com_node(nodelist[2]), clauses, elseNode)
    n.lineno = nodelist[0][2]
    return n

  def com_assign(self, node, assigning):
    # return a node suitable for use as an "lvalue"
    # loop to avoid trivial recursion
    while 1:
      t = node[0]
      if t == symbol.exprlist or t == symbol.testlist:
        if len(node) > 2:
          return self.com_assign_tuple(node, assigning)
        node = node[1]
      elif t in _assign_types:
        if len(node) > 2:
          raise SyntaxError, "can't assign to operator"
        node = node[1]
      elif t == symbol.power:
        if node[1][0] != symbol.atom:
          raise SyntaxError, "can't assign to operator"
        if len(node) > 2:
          primary = self.com_node(node[1])
          for i in range(2, len(node)-1):
            ch = node[i]
            if ch[0] == token.DOUBLESTAR:
              raise SyntaxError, "can't assign to operator"
            primary = self.com_apply_trailer(primary, ch)
          return self.com_assign_trailer(primary, node[-1], assigning)
        node = node[1]
      elif t == symbol.atom:
        t = node[1][0]
        if t == token.LPAR:
          node = node[2]
          if node[0] == token.RPAR:
            raise SyntaxError, "can't assign to ()"
        elif t == token.LSQB:
          node = node[2]
          if node[0] == token.RSQB:
            raise SyntaxError, "can't assign to []"
          return self.com_assign_list(node, assigning)
        elif t == token.NAME:
          return self.com_assign_name(node[1], assigning)
        else:
          raise SyntaxError, "can't assign to literal"
      else:
        raise SyntaxError, "bad assignment"

  def com_assign_tuple(self, node, assigning):
    assigns = [ ]
    for i in range(1, len(node), 2):
      assigns.append(self.com_assign(node[i], assigning))
    return Node('ass_tuple', assigns)

  def com_assign_list(self, node, assigning):
    assigns = [ ]
    for i in range(1, len(node), 2):
      assigns.append(self.com_assign(node[i], assigning))
    return Node('ass_list', assigns)

  def com_assign_name(self, node, assigning):
    return Node('ass_name', node[1], assigning)

  def com_assign_trailer(self, primary, node, assigning):
    t = node[1][0]
    if t == token.LPAR:
      raise SyntaxError, "can't assign to function call"
    if t == token.DOT:
      return self.com_assign_attr(primary, node[2], assigning)
    if t == token.LSQB:
      return self.com_subscriptlist(primary, node[2], assigning)
    raise SyntaxError, "unknown trailer type: %s" % t

  def com_assign_attr(self, primary, node, assigning):
    return Node('ass_attr', primary, node[1], assigning)

  def com_binary(self, type, nodelist):
    "Compile 'NODE (OP NODE)*' into (type, [ node1, ..., nodeN ])."
    if len(nodelist) == 1:
      return self.com_node(nodelist[0])
    items = [ ]
    for i in range(0, len(nodelist), 2):
      items.append(self.com_node(nodelist[i]))
    return Node(type, items)

  def com_stmt(self, node):
    #pprint.pprint(node)
    result = self.com_node(node)
    try:
      result[0]
    except:
      print node[0]
    if result[0] == 'stmt':
      return result
    return Node('stmt', [ result ])

  def com_append_stmt(self, stmts, node):
    result = self.com_node(node)
    try:
      result[0]
    except:
      print node
    if result[0] == 'stmt':
      stmts[len(stmts):] = result[1]
    else:
      stmts.append(result)

  def com_list_constructor(self, nodelist):
    values = [ ]
    for i in range(1, len(nodelist), 2):
      values.append(self.com_node(nodelist[i]))
    return Node('list', values)

  def com_dictmaker(self, nodelist):
    # dictmaker: test ':' test (',' test ':' value)* [',']
    items = [ ]
    for i in range(1, len(nodelist), 4):
      items.append(self.com_node(nodelist[i]), self.com_node(nodelist[i+2]))
    return Node('dict', items)

  def com_apply_trailer(self, primaryNode, nodelist):
    t = nodelist[1][0]
    if t == token.LPAR:
      return self.com_call_function(primaryNode, nodelist[2])
    if t == token.DOT:
      return self.com_select_member(primaryNode, nodelist[2])
    if t == token.LSQB:
      return self.com_subscriptlist(primaryNode, nodelist[2], OP_APPLY)

    raise SyntaxError, 'unknown node type: %s' % t

  def com_select_member(self, primaryNode, nodelist):
    if nodelist[0] != token.NAME:
      raise SyntaxError, "member must be a name"
    n = Node('getattr', primaryNode, nodelist[1])
    n.lineno = nodelist[2]
    return n

  def com_call_function(self, primaryNode, nodelist):
    if nodelist[0] == token.RPAR:
      return Node('call_func', primaryNode, [ ])
    args = [ ]
    kw = 0
    for i in range(1, len(nodelist), 2):
      kw, result = self.com_argument(nodelist[i], kw)
      args.append(result)
    return Node('call_func', primaryNode, args)

  def com_argument(self, nodelist, kw):
    if len(nodelist) == 2:
      if kw:
        raise SyntaxError, "non-keyword arg after keyword arg"
      return 0, self.com_node(nodelist[1])
    result = self.com_node(nodelist[3])
    n = nodelist[1]
    while len(n) == 2 and n[0] != token.NAME:
      n = n[1]
    if n[0] != token.NAME:
      raise SyntaxError, "keyword can't be an expression (%s)"%n[0]
    n = Node('keyword', n[1], result)
    n.lineno = result.lineno
    return 1, n

  def com_subscriptlist(self, primary, nodelist, assigning):
    # slicing:      simple_slicing | extended_slicing
    # simple_slicing:   primary "[" short_slice "]"
    # extended_slicing: primary "[" slice_list "]" 
    # slice_list:   slice_item ("," slice_item)* [","]

    # backwards compat slice for '[i:j]'
    if len(nodelist) == 2:
      sub = nodelist[1]
      if (sub[1][0] == token.COLON or \
              (len(sub) > 2 and sub[2][0] == token.COLON)) and \
             sub[-1][0] != symbol.sliceop:
        return self.com_slice(primary, sub, assigning)

    subscripts = [ ]
    for i in range(1, len(nodelist), 2):
      subscripts.append(self.com_subscript(nodelist[i]))

    return Node('subscript', primary, assigning, subscripts)

  def com_subscript(self, node):
    # slice_item: expression | proper_slice | ellipsis
    ch = node[1]
    if ch[0] == token.DOT and node[2][0] == token.DOT:
      return ('ellipsis', None)
    if ch[0] == token.COLON or len(node) > 2:
      return self.com_sliceobj(node)
    return self.com_node(ch)

  def com_sliceobj(self, node):
    # proper_slice: short_slice | long_slice
    # short_slice:  [lower_bound] ":" [upper_bound]
    # long_slice:   short_slice ":" [stride]
    # lower_bound:  expression
    # upper_bound:  expression
    # stride:       expression
    #
    # Note: a stride may be further slicing...

    items = [ ]

    if node[1][0] == token.COLON:
      items.append(Node('const', None))
      i = 2
    else:
      items.append(self.com_node(node[1]))
      # i == 2 is a COLON
      i = 3

    if i < len(node) and node[i][0] == symbol.test:
      items.append(self.com_node(node[i]))
      i = i + 1
    else:
      items.append(Node('const', None))

    # a short_slice has been built. look for long_slice now by looking
    # for strides...
    for j in range(i, len(node)):
      ch = node[j]
      if len(ch) == 2:
        items.append(Node('const', None))
      else:
        items.append(self.com_node(ch[2]))

    return Node('sliceobj', items)

  def com_slice(self, primary, node, assigning):
    # short_slice:  [lower_bound] ":" [upper_bound]
    lower = upper = None
    if len(node) == 3:
      if node[1][0] == token.COLON:
        upper = self.com_node(node[2])
      else:
        lower = self.com_node(node[1])
    elif len(node) == 4:
      lower = self.com_node(node[1])
      upper = self.com_node(node[3])
    return Node('slice', primary, assigning, lower, upper)

  def get_docstring(self, node, n=None):
    if n is None:
      n = node[0]
      node = node[1:]
    if n == symbol.suite:
      if len(node) == 1:
        return self.get_docstring(node[0])
      for sub in node:
        if sub[0] == symbol.stmt:
          return self.get_docstring(sub)
      return None
    if n == symbol.file_input:
      for sub in node:
        if sub[0] == symbol.stmt:
          return self.get_docstring(sub)
      return None
    if n == symbol.atom:
      if node[0][0] == token.STRING:
        s = ''
        for t in node:
          s = s + eval(t[1])
        return s
      return None
    if n == symbol.stmt or n == symbol.simple_stmt or n == symbol.small_stmt:
      return self.get_docstring(node[0])
    if n in _doc_nodes and len(node) == 1:
      return self.get_docstring(node[0])
    return None


_doc_nodes = [
  symbol.expr_stmt,
  symbol.testlist,
  symbol.test,
  symbol.and_test,
  symbol.not_test,
  symbol.comparison,
  symbol.expr,
  symbol.xor_expr,
  symbol.and_expr,
  symbol.shift_expr,
  symbol.arith_expr,
  symbol.term,
  symbol.factor,
  symbol.power,
  ]

# comp_op: '<' | '>' | '=' | '>=' | '<=' | '<>' | '!=' | '=='
#             | 'in' | 'not' 'in' | 'is' | 'is' 'not'
_cmp_types = {
  token.LESS : '<',
  token.GREATER : '>',
  token.EQEQUAL : '==',
  token.EQUAL : '==',
  token.LESSEQUAL : '<=',
  token.GREATEREQUAL : '>=',
  token.NOTEQUAL : '!=',
  }

_legal_node_types = [
  symbol.funcdef,
  symbol.classdef,
  symbol.stmt,
  symbol.small_stmt,
  symbol.flow_stmt,
  symbol.simple_stmt,
  symbol.compound_stmt,
  symbol.expr_stmt,
  symbol.print_stmt,
  symbol.del_stmt,
  symbol.pass_stmt,
  symbol.break_stmt,
  symbol.continue_stmt,
  symbol.return_stmt,
  symbol.raise_stmt,
  symbol.import_stmt,
  symbol.global_stmt,
  symbol.exec_stmt,
  symbol.assert_stmt,
  symbol.if_stmt,
  symbol.while_stmt,
  symbol.for_stmt,
  symbol.try_stmt,
  symbol.suite,
  symbol.testlist,
  symbol.test,
  symbol.and_test,
  symbol.not_test,
  symbol.comparison,
  symbol.exprlist,
  symbol.expr,
  symbol.xor_expr,
  symbol.and_expr,
  symbol.shift_expr,
  symbol.arith_expr,
  symbol.term,
  symbol.factor,
  symbol.power,
  symbol.atom,
  ]

_assign_types = [
  symbol.test,
  symbol.and_test,
  symbol.not_test,
  symbol.comparison,
  symbol.expr,
  symbol.xor_expr,
  symbol.and_expr,
  symbol.shift_expr,
  symbol.arith_expr,
  symbol.term,
  symbol.factor,
  ]

# Local Variables: 
# mode: python     
# indent-tabs-mode: nil 
# py-indent-offset: 2 
# py-smart-indentation: nil 
# End: