Add workaround for displaCy server on Python 2/3 (resolves #1227)

Make sure status and headers are bytes on Python 2 and strings on
Python 3

spacy/compat.py

@@ -61,6 +61,14 @@ elif is_python3:
     json_dumps = lambda data: ujson.dumps(data, indent=2)
     path2str = lambda path: str(path)
 
+
+def b_to_str(b_str):
+    if is_python2:
+        return b_str
+    # important: if no encoding is set, string becomes "b'...'"
+    return str(b_str, encoding='utf8')
+
+
 def getattr_(obj, name, *default):
     if is_python3 and isinstance(name, bytes):
         name = name.decode('utf8')

spacy/displacy/__init__.py

@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 
 from .render import DependencyRenderer, EntityRenderer
 from ..tokens import Doc
+from ..compat import b_to_str
 from ..util import prints, is_in_jupyter
 
 
@@ -65,7 +66,9 @@ def serve(docs, style='dep', page=True, minify=False, options={}, manual=False,
 
 
 def app(environ, start_response):
-    start_response('200 OK', [('Content-type', 'text/html; charset=utf-8')])
+    # headers and status need to be bytes in Python 2, see #1227
+    headers = [(b_to_str(b'Content-type'), b_to_str(b'text/html; charset=utf-8'))]
+    start_response(b_to_str(b'200 OK'), headers)
     res = _html['parsed'].encode(encoding='utf-8')
     return [res]