ref: 023d957e6b80f88584fdff30a95be6330613b27a
dir: /sys/lib/python/plat-irix5/panelparser.py/
# Module 'parser' # # Parse S-expressions output by the Panel Editor # (which is written in Scheme so it can't help writing S-expressions). # # See notes at end of file. whitespace = ' \t\n' operators = '()\'' separators = operators + whitespace + ';' + '"' # Tokenize a string. # Return a list of tokens (strings). # def tokenize_string(s): tokens = [] while s: c = s[:1] if c in whitespace: s = s[1:] elif c == ';': s = '' elif c == '"': n = len(s) i = 1 while i < n: c = s[i] i = i+1 if c == '"': break if c == '\\': i = i+1 tokens.append(s[:i]) s = s[i:] elif c in operators: tokens.append(c) s = s[1:] else: n = len(s) i = 1 while i < n: if s[i] in separators: break i = i+1 tokens.append(s[:i]) s = s[i:] return tokens # Tokenize a whole file (given as file object, not as file name). # Return a list of tokens (strings). # def tokenize_file(fp): tokens = [] while 1: line = fp.readline() if not line: break tokens = tokens + tokenize_string(line) return tokens # Exception raised by parse_exr. # syntax_error = 'syntax error' # Parse an S-expression. # Input is a list of tokens as returned by tokenize_*(). # Return a pair (expr, tokens) # where expr is a list representing the s-expression, # and tokens contains the remaining tokens. # May raise syntax_error. # def parse_expr(tokens): if (not tokens) or tokens[0] != '(': raise syntax_error, 'expected "("' tokens = tokens[1:] expr = [] while 1: if not tokens: raise syntax_error, 'missing ")"' if tokens[0] == ')': return expr, tokens[1:] elif tokens[0] == '(': subexpr, tokens = parse_expr(tokens) expr.append(subexpr) else: expr.append(tokens[0]) tokens = tokens[1:] # Parse a file (given as file object, not as file name). # Return a list of parsed S-expressions found at the top level. # def parse_file(fp): tokens = tokenize_file(fp) exprlist = [] while tokens: expr, tokens = parse_expr(tokens) exprlist.append(expr) return exprlist # EXAMPLE: # # The input # '(hip (hop hur-ray))' # # passed to tokenize_string() returns the token list # ['(', 'hip', '(', 'hop', 'hur-ray', ')', ')'] # # When this is passed to parse_expr() it returns the expression # ['hip', ['hop', 'hur-ray']] # plus an empty token list (because there are no tokens left. # # When a file containing the example is passed to parse_file() it returns # a list whose only element is the output of parse_expr() above: # [['hip', ['hop', 'hur-ray']]] # TOKENIZING: # # Comments start with semicolon (;) and continue till the end of the line. # # Tokens are separated by whitespace, except the following characters # always form a separate token (outside strings): # ( ) ' # Strings are enclosed in double quotes (") and backslash (\) is used # as escape character in strings.