我怎样才能漂亮地打印一个 nltk 树对象？

Question

我想以直观的方式查看下面的结果是否是我需要的：

import nltk 
sentence = [("the", "DT"), ("little", "JJ"), ("yellow", "JJ"), ("dog", "NN"), ("barked","VBD"), ("at", "IN"), ("the", "DT"), ("cat", "NN")]

pattern = """NP: {<DT>?<JJ>*<NN>}
VBD: {<VBD>}
IN: {<IN>}"""
NPChunker = nltk.RegexpParser(pattern) 
result = NPChunker.parse(sentence)

来源：

我不明白为什么我不能 pretty_print result。

result.pretty_print()

错误显示 TypeError: not all arguments converted during string formatting。我用的是Python3.5，nltk3.3。

Answer 1

如果您正在寻找带括号的解析输出，您可以使用 Tree.pprint():

>>> import nltk 
>>> sentence = [("the", "DT"), ("little", "JJ"), ("yellow", "JJ"), ("dog", "NN"), ("barked","VBD"), ("at", "IN"), ("the", "DT"), ("cat", "NN")]
>>> 
>>> pattern = """NP: {<DT>?<JJ>*<NN>}
... VBD: {<VBD>}
... IN: {<IN>}"""
>>> NPChunker = nltk.RegexpParser(pattern) 
>>> result = NPChunker.parse(sentence)
>>> result.pprint()
(S
  (NP the/DT little/JJ yellow/JJ dog/NN)
  (VBD barked/VBD)
  (IN at/IN)
  (NP the/DT cat/NN))

但您很可能正在寻找

                             S                                      
            _________________|_____________________________          
           NP                        VBD       IN          NP       
   ________|_________________         |        |      _____|____     
the/DT little/JJ yellow/JJ dog/NN barked/VBD at/IN the/DT     cat/NN

让我们深入研究 Tree.pretty_print() https://github.com/nltk/nltk/blob/develop/nltk/tree.py#L692 中的代码：

def pretty_print(self, sentence=None, highlight=(), stream=None, **kwargs):
    """
    Pretty-print this tree as ASCII or Unicode art.
    For explanation of the arguments, see the documentation for
    `nltk.treeprettyprinter.TreePrettyPrinter`.
    """
    from nltk.treeprettyprinter import TreePrettyPrinter
    print(TreePrettyPrinter(self, sentence, highlight).text(**kwargs),
          file=stream)

它正在创建一个 TreePrettyPrinter 对象，https://github.com/nltk/nltk/blob/develop/nltk/treeprettyprinter.py#L50

class TreePrettyPrinter(object):
    def __init__(self, tree, sentence=None, highlight=()):
        if sentence is None:
            leaves = tree.leaves()
            if (leaves and not any(len(a) == 0 for a in tree.subtrees())
                    and all(isinstance(a, int) for a in leaves)):
                sentence = [str(a) for a in leaves]
            else:
                # this deals with empty nodes (frontier non-terminals)
                # and multiple/mixed terminals under non-terminals.
                tree = tree.copy(True)
                sentence = []
                for a in tree.subtrees():
                    if len(a) == 0:
                        a.append(len(sentence))
                        sentence.append(None)
                    elif any(not isinstance(b, Tree) for b in a):
                        for n, b in enumerate(a):
                            if not isinstance(b, Tree):
                                a[n] = len(sentence)
                                sentence.append('%s' % b)
        self.nodes, self.coords, self.edges, self.highlight = self.nodecoords(
                tree, sentence, highlight)

看起来引发错误的行是 sentence.append('%s' % b) https://github.com/nltk/nltk/blob/develop/nltk/treeprettyprinter.py#L97

问题是为什么会引发 TypeError？

TypeError: not all arguments converted during string formatting

如果我们仔细看，看起来我们可以使用 print('%s' % b) 最基本的 python 类型

# String
>>> x = 'abc'
>>> type(x)
<class 'str'>
>>> print('%s' % x)
abc

# Integer
>>> x = 123
>>> type(x)
<class 'int'>
>>> print('%s' % x)
123

# Float 
>>> x = 1.23
>>> type(x)
<class 'float'>
>>> print('%s' % x)
1.23

# Boolean
>>> x = True
>>> type(x)
<class 'bool'>
>>> print('%s' % x)
True

令人惊讶的是，它甚至适用于列表！

>>> x = ['abc', 'def']
>>> type(x)
<class 'list'>
>>> print('%s' % x)
['abc', 'def']

但是它被tuple阻碍了！！

>>> x = ('DT', 123)
>>> x = ('abc', 'def')
>>> type(x)
<class 'tuple'>
>>> print('%s' % x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: not all arguments converted during string formatting

所以如果我们回到 https://github.com/nltk/nltk/blob/develop/nltk/treeprettyprinter.py#L95

处的代码

if not isinstance(b, Tree):
    a[n] = len(sentence)
    sentence.append('%s' % b)

因为我们知道 sentence.append('%s' % b) 无法处理 tuple，添加一个元组类型检查并以某种方式连接元组中的项目并转换为 str 将产生很好的效果pretty_print:

if not isinstance(b, Tree):
    a[n] = len(sentence)
    if type(b) == tuple:
        b = '/'.join(b)
    sentence.append('%s' % b)

[输出]:

                             S                                      
            _________________|_____________________________          
           NP                        VBD       IN          NP       
   ________|_________________         |        |      _____|____     
the/DT little/JJ yellow/JJ dog/NN barked/VBD at/IN the/DT     cat/NN

在不更改nltk代码的情况下，是否仍然可以获得漂亮的印刷品？

让我们看看 result 即 Tree 对象的样子：

Tree('S', [Tree('NP', [('the', 'DT'), ('little', 'JJ'), ('yellow', 'JJ'), ('dog', 'NN')]), Tree('VBD', [('barked', 'VBD')]), Tree('IN', [('at', 'IN')]), Tree('NP', [('the', 'DT'), ('cat', 'NN')])])

看起来叶子被保存为字符串元组列表，例如[('the', 'DT'), ('cat', 'NN')]，所以我们可以做一些修改，使其成为字符串列表，例如[('the/DT'), ('cat/NN')]，这样Tree.pretty_print()就可以很好玩了。

因为我们知道 Tree.pprint() 有助于将字符串元组连接成我们想要的形式，即

(S
  (NP the/DT little/JJ yellow/JJ dog/NN)
  (VBD barked/VBD)
  (IN at/IN)
  (NP the/DT cat/NN))

我们可以简单地输出到括号中的解析字符串，然后用 Tree.fromstring():

重新读取解析 Tree 对象

from nltk import Tree
Tree.fromstring(str(result)).pretty_print()

决赛：

import nltk 
sentence = [("the", "DT"), ("little", "JJ"), ("yellow", "JJ"), ("dog", "NN"), ("barked","VBD"), ("at", "IN"), ("the", "DT"), ("cat", "NN")]

pattern = """NP: {<DT>?<JJ>*<NN>}
VBD: {<VBD>}
IN: {<IN>}"""
NPChunker = nltk.RegexpParser(pattern) 
result = NPChunker.parse(sentence)

Tree.fromstring(str(result)).pretty_print()

[输出]:

                             S                                      
            _________________|_____________________________          
           NP                        VBD       IN          NP       
   ________|_________________         |        |      _____|____     
the/DT little/JJ yellow/JJ dog/NN barked/VBD at/IN the/DT     cat/NN

我怎样才能漂亮地打印一个 nltk 树对象？

How can I pretty print a nltk tree object?

python

tree

nltk

pprint