💫 Allow Span to take text label (#3031)

Fixes #3027.

* Allow Span.__init__ to take unicode values for the `label` argument.
* Allow `Span.label_` to be writeable.

- [x] I have submitted the spaCy Contributor Agreement.
- [x] I ran the tests, and all new and existing tests passed.
- [ ] My changes don't require a change to the documentation, or if they do, I've added all required information.

spacy/tests/doc/test_span.py

@@ -3,7 +3,7 @@ from __future__ import unicode_literals
 
 import pytest
 from spacy.attrs import ORTH, LENGTH
-from spacy.tokens import Doc
+from spacy.tokens import Doc, Span
 from spacy.vocab import Vocab
 
 from ..util import get_doc
@@ -154,6 +154,17 @@ def test_span_as_doc(doc):
     assert span.text == span_doc.text.strip()
 
 
+def test_span_string_label(doc):
+    span = Span(doc, 0, 1, label='hello')
+    assert span.label_ == 'hello'
+    assert span.label == doc.vocab.strings['hello']
+
+def test_span_string_set_label(doc):
+    span = Span(doc, 0, 1)
+    span.label_ = 'hello'
+    assert span.label_ == 'hello'
+    assert span.label == doc.vocab.strings['hello']
+
 def test_span_ents_property(doc):
     """Test span.ents for the """
     doc.ents = [

spacy/tokens/span.pyx

@@ -15,7 +15,7 @@ from ..parts_of_speech cimport univ_pos_t
 from ..util import normalize_slice
 from ..attrs cimport IS_PUNCT, IS_SPACE
 from ..lexeme cimport Lexeme
-from ..compat import is_config
+from ..compat import is_config, basestring_
 from ..errors import Errors, TempErrors, Warnings, user_warning, models_warning
 from .underscore import Underscore, get_ext_args
 
@@ -42,7 +42,7 @@ cdef class Span:
             raise ValueError(Errors.E046.format(name=name))
         return Underscore.span_extensions.pop(name)
 
-    def __cinit__(self, Doc doc, int start, int end, attr_t label=0,
+    def __cinit__(self, Doc doc, int start, int end, label=0,
                   vector=None, vector_norm=None):
         """Create a `Span` object from the slice `doc[start : end]`.
 
@@ -64,6 +64,8 @@ cdef class Span:
             self.end_char = self.doc[end - 1].idx + len(self.doc[end - 1])
         else:
             self.end_char = 0
+        if isinstance(label, basestring_):
+            label = doc.vocab.strings.add(label)
         if label not in doc.vocab.strings:
             raise ValueError(Errors.E084.format(label=label))
         self.label = label
@@ -601,6 +603,8 @@ cdef class Span:
         """RETURNS (unicode): The span's label."""
         def __get__(self):
             return self.doc.vocab.strings[self.label]
+        def __set__(self, unicode label_):
+            self.label = self.doc.vocab.strings.add(label_)
 
 
 cdef int _count_words_to_root(const TokenC* token, int sent_length) except -1: