Question

我是编程和使用Python的初学者。目前我正在尝试理解Jurafsky和Martin的2008年关于语音和语言处理的一些代码（关于语法分析的练习13.1）。我将在下面复制它（除了最后4行，我自己没有编写这段代码）。

我的问题很简单：我没有打印语法规则，而是得到如下输出：

set([<__main__.Rule object at 0x011E1810>, <__main__.Rule object at 0x011E1790>, <__main__.Rule object at 0x011E15F0>, ...)

我知道我应该用 str （自我）做一些事情，但我尝试了一些事情但仍然没有得到正常输出。我怀疑解决方案很简单，但我只是不知道该怎么做。很感谢任何形式的帮助。可能您不需要阅读和理解下面的所有代码，看看哪些代码无效。

非常感谢！

def chomsky_normal_form(grammar):
    grammar = set(grammar)
    nonterminals = set(rule.head for rule in grammar)

    # remove single symbol nonterminal rules
    for rule, symbol in _unary_rules(grammar, nonterminals):
        grammar.discard(rule)
        for rule2 in _rules_headed_by(grammar, symbol):
            grammar.add(Rule(rule.head, tuple(rule2.symbols)))
        if all(symbol not in rule.symbols for rule in grammar):
            for rule2 in _rules_headed_by(grammar, symbol):
                grammar.discard(rule2)

    # move terminals to their own rules
    for rule in list(grammar):
        if len(rule.symbols) >= 2:
            for i, symbol in enumerate(rule.symbols):
                if all(rule.head != symbol for rule in grammar):
                    rule = _new_symbol(grammar, rule, i, i + 1)

    # ensure there are only two nonterminals per rule
    for rule in _multi_symbol_rules(grammar):
        _new_symbol(grammar, rule, 0, 2)

    # return the grammar in CNF
    return grammar

# find A -> B rules, allowing concurrent modifications
def _unary_rules(grammar, nonterminals):
    while True:
        g = ((rule, rule.symbols[0])
            for rule in grammar
            if len(rule.symbols) == 1
            if rule.symbols[0] in nonterminals)
        yield g.next()

# find all rules headed by the given symbol
def _rules_headed_by(grammar, symbol):
    return [rule for rule in grammar if rule.head == symbol]

# create a new symbol which derives the given span of symbols
def _new_symbol(grammar, rule, start, stop):
    symbols = rule.symbols
    new_head = '_'.join(symbols[start:stop]).upper()
    new_symbols = symbols[:start] + (new_head,) + symbols[stop:]
    new_rule = Rule(rule.head, new_symbols)
    grammar.discard(rule)
    grammar.add(new_rule)
    grammar.add(Rule(new_head, symbols[start:stop]))
    return new_rule

# find A -> BCD... rules, allowing concurrent modifications
def _multi_symbol_rules(grammar):
    while True:
        g = (rule for rule in grammar if len(rule.symbols) >= 3)
        yield g.next()

# representation of a rule A -> B...C
class Rule(object):
    def __init__(self, head, symbols):
        self.head = head
        self.symbols = symbols
        self._key = head, symbols
    def __eq__(self, other):
        return self._key == other._key
    def __hash__(self):
        return hash(self._key)
    def __str__(self):
        rep = grammar_cnf
        return rep

# build a grammar from a string of lines like "X -> YZ | b"
def get_grammar(string):
    grammar = set()
    for line in string.splitlines():
        head, symbols_str = line.split(' -> ')
        for symbols_str in symbols_str.split(' | '):
            symbols = tuple(symbols_str.split())
            grammar.add(Rule(head, symbols))
    return grammar


grammar = get_grammar("""S -> NP VP | Aux NP VP | VP
NP -> Pronoun | Proper-Noun | Det Nominal
Nominal -> Noun | Nominal Noun | Nominal PP
VP -> Verb | Verb NP | Verb NP PP | Verb PP | VP PP
PP -> Preposition NP
Det -> that | this | a
Noun -> book | flight | meal | money
Verb -> book | include | prefer
Pronoun -> I | she | me
Proper-Noun -> Houston | TWA
Aux -> does
Preposition -> from | to | on | near | through""")

grammar_cnf = chomsky_normal_form(grammar)
print(grammar_cnf)

Answer 1

您可以在规则类

中实现__repr__

您可以使用__str__进行非正式演示，（如果 str 不存在，则会回退到 repr

这些都是这样的：

class Rule(object):

   def __init__(self, name):
     self.name = name

   def __repr__(self):
      return 'Rule({0})'.format(self.name)    

   def __str__(self):
     return self.name


rule = Rule('test')
print(rule) # test

python - 我打印涉及对象的东西有困难

1 个答案: