Fix last bug

2 files changed, 6 insertions, 6 deletions

diff --git a/pint/context.py b/pint/context.py
index bce99da..ea06d9e 100644
--- a/pint/context.py
+++ b/pint/context.py
@@ -201,7 +201,7 @@ class ContextChain(ChainMap):
     def __init__(self):
         super(ContextChain, self).__init__()
         self._graph = None
-        self._contexts = ()
+        self._contexts = []
 
     def insert_contexts(self, *contexts):
         """Insert one or more contexts in reversed order the chained map.
@@ -210,7 +210,7 @@ class ContextChain(ChainMap):
         To facilitate the identification of the context with the matching rule,
         the *relation_to_context* dictionary of the context is used.
         """
-        self._contexts = contexts + self._contexts
+        self._contexts.insert(0, contexts)
         self.maps = [ctx.relation_to_context for ctx in reversed(contexts)] + self.maps
         self._graph = None
 
@@ -246,4 +246,4 @@ class ContextChain(ChainMap):
         return self[(src, dst)].transform(src, dst, registry, value)
 
     def __hash__(self):
-        return hash(self._contexts)
+        return hash(tuple(self._contexts))
diff --git a/pint/registry.py b/pint/registry.py
index 7d9fdbb..b9ff71c 100644
--- a/pint/registry.py
+++ b/pint/registry.py
@@ -80,7 +80,7 @@ class _Meta(type):
         return obj
 
 
-class RegistryCache(object):
+class RegistryCache:
     """Cache to speed up unit registries
     """
 
@@ -1083,7 +1083,7 @@ class ContextRegistry(BaseRegistry):
         #: Map context chain to cache
         self._caches = {}
 
-        super(ContextRegistry, self).__init__(**kwargs)
+        super().__init__(**kwargs)
 
     def _register_parsers(self):
         super(ContextRegistry, self)._register_parsers()
@@ -1132,7 +1132,7 @@ class ContextRegistry(BaseRegistry):
         try:
             self._cache = self._caches[self._active_ctx]
         except KeyError:
-            super(ContextRegistry, self)._build_cache()
+            super()._build_cache()
             self._caches[self._active_ctx] = self._cache
 
     def enable_contexts(self, *names_or_contexts, **kwargs):