索引错误：索引 -1 超出轴 0 的范围，大小为 0

Question

当我尝试使用 ngrams 实现文本生成器时，我从 scipy 得到一个索引 -1 超出轴 0 的范围，大小为 0 错误。

Traceback (most recent call last):
  File "C:\Users\hp\PycharmProjects\N-gram poems\trigram_model.py", line 125, in <module>
    generate()
  File "C:\Users\hp\PycharmProjects\N-gram poems\trigram_model.py", line 118, in generate
    singleverse(int(c))
  File "C:\Users\hp\PycharmProjects\N-gram poems\trigram_model.py", line 80, in singleverse
    result = stats.multinomial.rvs(1, word_probabilities)
  File "C:\Users\hp\PycharmProjects\N-gram poems\venv\lib\site-packages\scipy\stats\_multivariate.py", line 3242, in rvs
    n, p, npcond = self._process_parameters(n, p)
  File "C:\Users\hp\PycharmProjects\N-gram poems\venv\lib\site-packages\scipy\stats\_multivariate.py", line 3036, in _process_parameters
    p[..., -1] = 1. - p[..., :-1].sum(axis=-1)
IndexError: index -1 is out of bounds for axis 0 with size 0

它在 for 循环中，每次发生错误时都会发生变化。有时它根本不会发生。它主要发生在接近程序结束时。

这是发生错误的代码：

def singleverse(num):
    TrTrigrams = [((filtered_tokens[i], filtered_tokens[i + 1]), filtered_tokens[i + 2]) for i in
                  range(len(filtered_tokens) - 2)]
    TrTrigramCFD = nltk.ConditionalFreqDist(TrTrigrams)
    TrTrigramPbs = nltk.ConditionalProbDist(TrTrigramCFD, nltk.MLEProbDist)

    rand = random.choice(random_choice_list)
    start_word = ('<s>', rand)
    data = []
    for i in range(10):
        probable_words = list(TrTrigramPbs[start_word].samples())
        word_probabilities = [TrTrigramPbs[start_word].prob(word) for word in probable_words]
        result = stats.multinomial.rvs(1, word_probabilities)
        index_of_probable_word = list(result).index(1)
        start_word = (start_word[1], (probable_words[index_of_probable_word]))
        data.append(start_word[1])
    line = []
    for i in data:
        if i != "<s>" and i != "</s>":
            line.append(i)
    poem_line = ' '.join([str(i) for i in line]).capitalize()
    print(poem_line)


def generate():
    """Generates the final poem with user input of structure."""
    print("What structure do you want?(e.g., 3 x 4, 2 x 4, 2 x 5): ")
    while True:
        try:
            x, y, z = input().split()
        except:
            print("Enter the structure as shown above.")
            continue
        break

    while True:
        try:
            for stanza in range(1):
                for first_verse in range(1):
                    b = random.randint(7, 12)
                    firstverse(int(b))
                for verse in range(int(z) - 1):
                    a = random.randint(7, 12)
                    singleverse(int(a))
                print('\n')
            for stanza in range(int(x) - 1):
                for verse in range(int(z)):
                    c = random.randint(7, 12)
                    singleverse(int(c))
                print('\n')
        except KeyError:
            print("This was not a valid seed word please try again.")
            continue
        break

generate()