python - 带有单引号、双引号或三引号的 Lex 字符串

Question

我的目标是像 Python 那样解析字符串。

问题:如何编写 lex 来支持以下内容:

1. “字符串...”
2. '字符串...'
3. """多行字符串\n\n end"""
4. '''多行字符串\n\n end'''

部分代码:

states = (        ('string', 'exclusive'),        )# Stringsdef t_begin_string(self, t):    r'(\'|(\'{3})|\"|(\"{3}))'    t.lexer.push_state('string')def t_string_end(self, t):    r'(\'|(\'{3})|\"|(\"{3}))'    t.lexer.pop_state()def t_string_newline(self, t):    r'\n'    t.lexer.lineno += 1def t_string_error(self, t):    print("Illegal character in string '%s'" % t.value[0])    t.lexer.skip(1)

---

我目前的想法是创建4 种独特的状态，以匹配 4 种不同的字符串大小写，但我想知道是否有更好的方法。

感谢您的帮助!

Answer 1

隔离公共(public)字符串以形成单一状态并尝试构建具有较少状态的自动机但是如果您不担心使用外部库使您的工作更轻松，您可以查看 py lex yacc

但是你需要 lex yacc 的基础知识///示例代码如图所示

tokens = (
    'NAME','NUMBER',
    'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
    'LPAREN','RPAREN',
    )
    enter code here

# Tokens

t_PLUS    = r'\+'
t_MINUS   = r'-'
t_TIMES   = r'\*'
t_DIVIDE  = r'/'
t_EQUALS  = r'='
t_LPAREN  = r'\('
t_RPAREN  = r'\)'
t_NAME    = r'[a-zA-Z_][a-zA-Z0-9_]*'

def t_NUMBER(t):
    r'\d+'
    try:
        t.value = int(t.value)
    except ValueError:
        print("Integer value too large %d", t.value)
        t.value = 0
    return t

# Ignored characters
t_ignore = " \t"

def t_newline(t):
    r'\n+'
    t.lexer.lineno += t.value.count("\n")

def t_error(t):
    print("Illegal character '%s'" % t.value[0])
    t.lexer.skip(1)

# Build the lexer
import ply.lex as lex
lex.lex()

# Parsing rules

precedence = (
    ('left','PLUS','MINUS'),
    ('left','TIMES','DIVIDE'),
    ('right','UMINUS'),
    )

# dictionary of names
names = { }

def p_statement_assign(t):
    'statement : NAME EQUALS expression'
    names[t[1]] = t[3]

def p_statement_expr(t):
    'statement : expression'
    print(t[1])

def p_expression_binop(t):
    '''expression : expression PLUS expression
                  | expression MINUS expression
                  | expression TIMES expression
                  | expression DIVIDE expression'''
    if t[2] == '+'  : t[0] = t[1] + t[3]
    elif t[2] == '-': t[0] = t[1] - t[3]
    elif t[2] == '*': t[0] = t[1] * t[3]
    elif t[2] == '/': t[0] = t[1] / t[3]

def p_expression_uminus(t):
    'expression : MINUS expression %prec UMINUS'
    t[0] = -t[2]

def p_expression_group(t):
    'expression : LPAREN expression RPAREN'
    t[0] = t[2]

def p_expression_number(t):
    'expression : NUMBER'
    t[0] = t[1]

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_error(t):
    print("Syntax error at '%s'" % t.value)

import ply.yacc as yacc
yacc.yacc()

while 1:
    try:
        s = input('calc > ')   # Use raw_input on Python 2
    except EOFError:
        break
    yacc.parse(s)