How to get the dependency tree with spaCy?
I don't know if this is a new API call or what, but there's a .print_tree() method on the Document class that makes quick work of this.
https://spacy.io/api/doc#print_tree
It dumps the dependency tree to JSON. It deals with multiple sentence roots and all that :
import spacy
nlp = spacy.load('en')
doc1 = nlp(u'This is the way the world ends. So you say.')
print(doc1.print_tree(light=True))
The name print_tree is a bit of a misnomer, the method itself doesn't print anything, rather it returns a list of dicts, one for each sentence.
In case someone wants to easily view the dependency tree produced by spacy, one solution would be to convert it to an nltk.tree.Tree
and use the nltk.tree.Tree.pretty_print
method. Here is an example:
import spacy
from nltk import Tree
en_nlp = spacy.load('en')
doc = en_nlp("The quick brown fox jumps over the lazy dog.")
def to_nltk_tree(node):
if node.n_lefts + node.n_rights > 0:
return Tree(node.orth_, [to_nltk_tree(child) for child in node.children])
else:
return node.orth_
[to_nltk_tree(sent.root).pretty_print() for sent in doc.sents]
Output:
jumps
________________|____________
| | | | | over
| | | | | |
| | | | | dog
| | | | | ___|____
The quick brown fox . the lazy
Edit: For changing the token representation you can do this:
def tok_format(tok):
return "_".join([tok.orth_, tok.tag_])
def to_nltk_tree(node):
if node.n_lefts + node.n_rights > 0:
return Tree(tok_format(node), [to_nltk_tree(child) for child in node.children])
else:
return tok_format(node)
Which results in:
jumps_VBZ
__________________________|___________________
| | | | | over_IN
| | | | | |
| | | | | dog_NN
| | | | | _______|_______
The_DT quick_JJ brown_JJ fox_NN ._. the_DT lazy_JJ
You can use the library below to view your dependency tree, found it extremely helpful!
import spacy
from spacy import displacy
nlp = spacy.load('en')
doc = nlp(u'This is a sentence.')
displacy.serve(doc, style='dep')
You can open it with your browser, and it looks like:
To generate a SVG file:
from pathlib import Path
output_path = Path("yourpath/.svg")
svg = displacy.render(doc, style='dep')
with output_path.open("w", encoding="utf-8") as fh:
fh.write(svg)
The tree isn't an object in itself; you just navigate it via the relationships between tokens. That's why the docs talk about navigating the tree, but not 'getting' it.
First, let's parse some text to get a Doc
object:
>>> import spacy
>>> nlp = spacy.load('en_core_web_sm')
>>> doc = nlp('First, I wrote some sentences. Then spaCy parsed them. Hooray!')
doc
is a Sequence
of Token
objects:
>>> doc[0]
First
>>> doc[1]
,
>>> doc[2]
I
>>> doc[3]
wrote
But it doesn't have a single root token. We parsed a text made up of three sentences, so there are three distinct trees, each with their own root. If we want to start our parsing from the root of each sentence, it will help to get the sentences as distinct objects, first. Fortunately, doc
exposes these to us via the .sents
property:
>>> sentences = list(doc.sents)
>>> for sentence in sentences:
... print(sentence)
...
First, I wrote some sentences.
Then spaCy parsed them.
Hooray!
Each of these sentences is a Span
with a .root
property pointing to its root token. Usually, the root token will be the main verb of the sentence (although this may not be true for unusual sentence structures, such as sentences without a verb):
>>> for sentence in sentences:
... print(sentence.root)
...
wrote
parsed
Hooray
With the root token found, we can navigate down the tree via the .children
property of each token. For instance, let's find the subject and object of the verb in the first sentence. The .dep_
property of each child token describes its relationship with its parent; for instance a dep_
of 'nsubj'
means that a token is the nominal subject of its parent.
>>> root_token = sentences[0].root
>>> for child in root_token.children:
... if child.dep_ == 'nsubj':
... subj = child
... if child.dep_ == 'dobj':
... obj = child
...
>>> subj
I
>>> obj
sentences
We can likewise keep going down the tree by viewing one of these token's children:
>>> list(obj.children)
[some]
Thus with the properties above, you can navigate the entire tree. If you want to visualise some dependency trees for example sentences to help you understand the structure, I recommend playing with displaCy.