I've been using ply & have extended the example slightly:
[code]
<code>
import ply.lex as lex
reserved = {'print':'PRINT', 'quit' : 'QUIT'}
# List of token names. This is always required
tokens = [
'NUMBER',
'NAME',
'PLUS',
'MINUS',
'TIMES',
'DIVIDE',
'LPAREN',
'RPAREN',
'EQUALS',
'STRING',
] + list(reserved.values())
# Regular expression rules for simple tokens
t_PLUS = r'\+'
t_MINUS = r'-'
t_TIMES = r'\*'
t_DIVIDE = r'/'
t_LPAREN = r'\('
t_RPAREN = r'\)'
t_EQUALS = r'='
def t_NAME(t):
r'[a-zA-Z_][a-zA-Z_0-9]*'
t.type = reserved.get(t.value,'NAME') # Check for reserved
words
return t
# A regular expression rule with some action code
def t_NUMBER(t):
r'\d+'
t.value = int(t.value)
return t
# Define a rule so we can track line numbers
def t_newline(t):
r'\n+'
t.lexer.lineno += len(t.value)
def t_STRING(t):
r'\"([^\\"]|(\\.))*\"'
escaped = 0
str = t.value[1:-1]
new_str = ""
for i in range(0, len(str)):
c = str[i]
if escaped:
if c == "n":
c = "\n"
elif c == "t":
c = "\t"
new_str += c
escaped = 0
else:
if c == "\\":
escaped = 1
else:
new_str += c
t.value = new_str
return t
# A string containing ignored characters (spaces and tabs)
t_ignore = ' \t'
# Error handling rule
def t_error(t):
print "Illegal character '%s'" % t.value[0]
t.lexer.skip(1)
# Build the lexer
lexer = lex.lex()
[/code]
</code>
&
[code]
<code>
import ply.yacc as yacc
import sys
# Get the token map from the lexer. This is required.
from calclex import tokens
names = {}
def p_statement_assign(t):
'statement : NAME EQUALS expression'
names[t[1]] = t[3]
def p_statement_expr(t):
'statement : expression'
if t[1] != None:
print t[1]
else:
pass
def p_expression_name(t):
'expression : NAME'
try:
t[0] = names[t[1]]
except LookupError:
print "Undefined name '%s'" % t[1]
t[0] = 0
def p_expression_plus(p):
'expression : expression PLUS term'
p[0] = p[1] + p[3]
def p_expression_minus(p):
'expression : expression MINUS term'
p[0] = p[1] - p[3]
def p_expression_term(p):
'expression : term'
p[0] = p[1]
def p_term_times(p):
'term : term TIMES factor'
p[0] = p[1] * p[3]
def p_term_div(p):
'term : term DIVIDE factor'
p[0] = p[1] / p[3]
def p_term_factor(p):
'term : factor'
p[0] = p[1]
def p_factor_num(p):
'factor : NUMBER'
p[0] = p[1]
def p_factor_expr(p):
'factor : LPAREN expression RPAREN'
p[0] = p[2]
def p_print(p):
'''expression : PRINT LPAREN STRING RPAREN
| PRINT LPAREN expression RPAREN'''
p[0] = p[3]
def p_quit(p):
'expression : QUIT'
sys.exit()
# Error rule for syntax errors
def p_error(p):
print "Syntax error in input!"
# Build the parser
parser = yacc.yacc()
if len(sys.argv) == 1:
while True:
try:
s = raw_input('calc > ')
except EOFError:
break
if not s: continue
result = parser.parse(s)
print result
elif sys.argv[1] == "-f":
f = open(sys.argv[2], "r")
s = f.readlines()
for line in s:
result = parser.parse(line)
if result != None:
print "result != none"
print result
[/code]
</code>
When I run print("hello") it says:
hello
none
calc>
What's wrong?
I also posted it at http://ubuntuforums.org/showthread.php?p=6698006#post6698006
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