文件输入任意文法，求每个VN的first（）、follow（）集合写出完整的可运行python代码

文件输入任意文法并计算文法中各个变量的第一集(first set)和跟随集(follow set)，通常涉及到上下文无关文法(CFG)分析。这里是一个简化版的Python代码示例，它使用了`pyparsing`库来解析文法，然后手动计算first和follow集合。请注意，这只是一个基本的示例，实际应用中可能需要更复杂的解析器和算法。

import pyparsing as pp

# 假设我们有如下的简单文法作为字符串输入
grammar_str = r"""
S -> A B
A -> a | ε
B -> b | ε
"""

def compute_first_and_follow(grammar):
    def first_var(var):
        if var == 'ε':
            return set()
        elif var.isupper():
            return {var}
        else:
            return {var} | {',' + next_term for term in grammar if term[0] == var}

    def follow_var(var):
        nonterminals = {rule.lhs() for rule in grammar if rule.rhs()[0] == var}
        if var in nonterminals:
            # 变量是终结符，follow集包含其后的终结符
            follow_set = {'$'}
        else:
            follow_set = {',' + next_term for rule in grammar if rule.lhs() == var[-1]}
        return follow_set

    grammar_obj = pp.parseString(grammar_str)
    rules = [(rule.name(), rule.asList()) for rule in grammar_obj]
    first_dict = {rule[0]: first_var(rule[0]) for rule in rules}
    follow_dict = {}
    
    for rule, terms in rules:
        if len(terms) > 1:
            last_nonterminal = terms[-2].upper()
            follow_dict[last_nonterminal] = follow_dict.get(last_nonterminal, set()) | follow_var(rule)

    return first_dict, follow_dict

# 示例用法
first, follow = compute_first_and_follow(grammar_str)
print("First sets:")
for k, v in first.items():
    print(f"{k}: {v}")

print("\nFollow sets:")
for k, v in follow.items():
    print(f"{k}: {v}")