我在使用 PLY 时遇到问题。我一直在读documentation并决定尝试一下这些例子。词法分析示例运行良好,但解析我无法开始工作。我还查看了文档,不明白如何将 lex 和 yacc 连接在一起以创建正确的编译器。解析器仅包含词法分析器的可能标记,据我所知,没有其他信息。
我添加了一些内容,例如颜色(Colorama 模块)和略有不同的消息,但除此之外,这与示例相同:
#!/usr/bin/env python
### LEXICAL ANALYSIS ###
import ply.lex as lex
import colorama
colorama.init()
tokens = (
"NUMBER",
"PLUS",
"MINUS",
"MULTIPLY",
"DIVIDE",
"LBRACKET",
"RBRACKET"
)
t_PLUS = r"\+"
t_MINUS = r"-"
t_MULTIPLY = r"\*"
t_DIVIDE = r"/"
t_LBRACKET = r"\("
t_RBRACKET = r"\)"
t_ignore = "\t\r "
def t_NUMBER(t):
r"\d+"
t.value = int(t.value)
return t
def t_newline(t):
r"\n+"
t.lexer.lineno += len(t.value)
def t_COMMENT(t):
r"\#.*"
print "Comment:", t.value
def t_error(t):
print colorama.Fore.RED + "\n\nLEXICAL ERROR: line", t.lexer.lineno, "and position", t.lexer.lexpos, "invalid token:", t.value.split("\n")[0] + colorama.Fore.RESET
t.lexer.skip(len(t.value))
def mylex(inp):
lexer = lex.lex()
lexer.input(inp)
for token in lexer:
print "Token:", token
这工作正常,但是解析器却不能:
#!/usr/bin/env python
import ply.yacc as yacc
from langlex import tokens
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 MULTIPLY 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 : LBRACKET expression RBRACKET"
p[0] = p[2]
def p_error(p):
print "Syntax error!"
parser = yacc.yacc()
while True:
s = raw_input("calc > ")
if not(s):
continue
result = parser.parse(s)
print result
当我尝试运行它时,出现以下错误:
calc > 5 + 10
Traceback (most recent call last):
File "C:\Users\Max\Desktop\lang\langyacc.py", line 49, in <module>
result = parser.parse(s)
File "C:\Python27\lib\site-packages\ply\yacc.py", line 265, in parse
return self.parseopt_notrack(input,lexer,debug,tracking,tokenfunc)
File "C:\Python27\lib\site-packages\ply\yacc.py", line 881, in parseopt_notrack
lexer = lex.lexer
AttributeError: 'module' object has no attribute 'lexer'
我是 lex、yacc 和编译器开发的初学者,不知道为什么会发生这种情况。任何帮助将不胜感激。
最佳答案
您尚未在词法分析器文件中构建词法分析器。您在函数 mylex()
中拥有它,但它实际上并未构建。
将其从函数中拉出。
lexer = lex.lex()
def mylex(inp):
lexer.input(inp)
# etc.
关于python - PLY Lex 和 Yacc 问题,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/25712334/