add extensible get_env hook on Spawner

to make it easier for subclasses to modify the env

jupyterhub/spawner.py

@@ -183,6 +183,14 @@ class Spawner(LoggingConfigurable):
         """
         self.api_token = ''
     
+    def get_env(self):
+        """Return the environment we should use
+        
+        Default returns a copy of self.env.
+        Use this to access the env in Spawner.start to allow extension in subclasses.
+        """
+        return self.env.copy()
+    
     def get_args(self):
         """Return the arguments to be passed after self.cmd"""
         args = [
@@ -376,9 +384,11 @@ class LocalProcessSpawner(Spawner):
             env['SHELL'] = shell
         return env
     
-    def _env_default(self):
-        env = super()._env_default()
-        return self.user_env(env)
+    def get_env(self):
+        """Add user environment variables"""
+        env = super().get_env()
+        env = self.user_env(env)
+        return env
     
     @gen.coroutine
     def start(self):
@@ -387,7 +397,7 @@ class LocalProcessSpawner(Spawner):
             self.user.server.ip = self.ip
         self.user.server.port = random_port()
         cmd = []
-        env = self.env.copy()
+        env = self.get_env()
         
         cmd.extend(self.cmd)
         cmd.extend(self.get_args())