remove dependency on IPython

- Standalone traitlets has been released, use it directly.
- Copy url_path_join from notebook

jupyterhub/utils.py

@@ -14,11 +14,6 @@ from tornado import web, gen, ioloop
 from tornado.httpclient import AsyncHTTPClient, HTTPError
 from tornado.log import app_log
 
-try:
-    from jupyter_notebook.utils import url_path_join
-except:
-    from IPython.html.utils import url_path_join
-
 
 def random_port():
     """get a single random port"""
@@ -172,5 +167,26 @@ def compare_token(compare, token):
     if compare == hashed:
         return True
     return False
-    
 
+
+def url_path_join(*pieces):
+    """Join components of url into a relative url
+
+    Use to prevent double slash when joining subpath. This will leave the
+    initial and final / in place
+    
+    Copied from notebook.utils.url_path_join
+    """
+    initial = pieces[0].startswith('/')
+    final = pieces[-1].endswith('/')
+    stripped = [ s.strip('/') for s in pieces ]
+    result = '/'.join(s for s in stripped if s)
+
+    if initial:
+        result = '/' + result
+    if final:
+        result = result + '/'
+    if result == '//':
+        result = '/'
+
+    return result