Add dependency patterns example

examples/dependency_patterns.py

@@ -0,0 +1,33 @@
+'''
+Match a dependency pattern. See https://github.com/explosion/spaCy/pull/1120
+
+We start by creating a DependencyTree for the Doc. This class models the document
+dependency tree. Then we compile the query into a Pattern using the PatternParser.
+The syntax is quite simple:
+
+we define a node named 'fox', that must match in the dep tree a token
+whose orth_ is 'fox'. an anonymous token whose lemma is 'quick' must have fox
+as parent, with a dep_ matching the regex am.* another anonymous token whose
+orth_ matches the regex brown|yellow has fox as parent, with whathever dep_
+DependencyTree.match returns a list of PatternMatch. Notice that we can assign
+names to anonymous or defined nodes ([word:fox]=f). We can get the Token mapped
+to the fox node using match['f'].
+'''
+import spacy
+from spacy.pattern import PatternParser, DependencyTree
+
+nlp = spacy.load('en')
+doc = nlp("The quick brown fox jumped over the lazy dog.")
+tree = DependencyTree(doc)
+
+query = """fox [word:fox]=f
+           [lemma:quick]=q >/am.*/ fox
+           [word:/brown|yellow/] > fox"""
+
+pattern = PatternParser.parse(query)
+matches = tree.match(pattern)
+
+assert len(matches) == 1
+match = matches[0]
+
+assert match['f'] == doc[3]