sexpr_parser.py

# $ProjectHeader: sexprmodule 0.2.1 Wed, 05 Apr 2000 23:33:53 -0600 nas $
# originally from: http://arctrix.com/nas/python/ 
# modified to understand \-escaped quotes instead of "" escaping  - pj 20060809
# IPC: taken from http://code.google.com/p/mhi/source/browse/sexpr.py  11 Jul 2011
import string
import StringIO
from StringIO import StringIO
# tokens
[T_EOF, T_ERROR, T_SYMBOL, T_STRING, 
 T_INTEGER, T_FLOAT, T_OPEN, T_CLOSE] = range(8)
# states
[S_START, S_SYMBOL, S_STRING, S_NUMBER] = range(4)

SexprError = 'SexprError'

def parse(expr): 
  return SexprParser(StringIO(expr)).parse()

class SexprParser:
  def __init__(self, input):
    self.line_no = 1
    self.input = input
    self.char = None

  def getc(self):
    if self.char is None:
      c = self.input.read(1)
      if c == '\n':
        self.line_no = self.line_no + 1
      return c
    else:
      t = self.char
      self.char = None
      return t

  def ungetc(self, c):
    self.char = c
    
  def convert_number(self, token):
    try:
      i = string.atoi(token)
      return (T_INTEGER, i)
    except ValueError:
      try:
        f = string.atof(token)
        return (T_FLOAT, f)
      except ValueError:
        return (T_ERROR, '%d: invalid number "%s"' % (self.line_no, token))

  def get_token(self):
    token = []
    state = S_START
    while 1:
      c = self.getc()
      if state == S_START:
        # EOF
        if not c:
          return (T_EOF, None)
        # whitespace
        elif c in ' \t\n':
          continue
        # comments
        elif c == ';':
          while c and (c != '\n'):
            c = self.getc()
        elif c == '(':
          return (T_OPEN, None)
        elif c == ')':
          return (T_CLOSE, None)
        elif c == '"':
          state = S_STRING
        elif c in '-0123456789.':
          state = S_NUMBER
          token.append(c)
        else:
          state = S_SYMBOL
          token.append(c)
      elif state == S_SYMBOL:
        if not c:
          return (T_SYMBOL, string.join(token, ''))
        if c in ' \t\n;()':
          self.ungetc(c)
          return (T_SYMBOL, string.join(token, ''))
        else:
          token.append(c)
      elif state == S_STRING:
        if not c:
          return (T_ERROR, '%d: unexpected EOF inside string' % self.line_no)
        elif c == '\\':
          c = self.getc()
          if c == '"':
            token.append('"')
          else:
            self.ungetc(c)
            token.append('\\')
        elif c == '"':
          return (T_STRING, string.join(token, ''))
        else:
          token.append(c)
      elif state == S_NUMBER:
        if not c:
          return self.convert_number(string.join(token, ''))
        if c in ' \t\n;()':
          self.ungetc(c)
          return self.convert_number(string.join(token, ''))
        elif c in '0123456789.eE-':
          token.append(c)
        else:
          return (T_ERROR, '%d: invalid character "%s" while reading integer' 
                    % (self.line_no, c))

  def parse(self, t=None):
    if not t:
      (t, v) = self.get_token()
    if t == T_OPEN:
      l = []
      while 1:
        (t, v) = self.get_token()
        if t == T_CLOSE:
          return l
        elif t == T_OPEN:
          v = self.parse(t)
          if v == None:
            raise SexprError, '%d: unexpected EOF' % self.line_no
        elif t == T_ERROR:
          raise SexprError, v
        elif t == T_EOF:
          raise SexprError, '%d: EOF while inside list' % self.line_no
        l.append(v)
    elif t == T_CLOSE:
      raise SexprError, '%d: unexpected )' % self.line_no
    elif t == T_EOF:
      return None
    elif t == T_ERROR:
      raise SexprError, v
    else:
      return v

if __name__ == '__main__':
  import sys
  #import profile
  p = SexprParser(sys.stdin)
  #profile.run('p.parse()')
  while 1:
    e = p.parse()
    print e
    if not e:
      break