fix: make dogpile.cache.memory preserve its init parameters

Make the `MemoryBackend` behave like the others, and stop removing keys
from the initialization dict.

Fixes: #273
Closes: #274
Pull-request: #274
Pull-request-sha: b893879

Change-Id: Ifd3f0d88b18a73a0ce287e1a514a6268daf157c4

Author: 0xDEC0DE

docs/build/unreleased/273.rst

@@ -0,0 +1,9 @@
+.. change::
+    :tags: bug, memory
+    :tickets: 273
+
+    Fixed issue where :meth:`.MemoryBackend.configure` would unexpectedly
+    modify the input arguments dictionary by removing its contents. The method
+    now preserves the original arguments dictionary as expected, consistent
+    with the behavior of other backend types.  Pull request courtesy Nicolas
+    Simonds.

dogpile/cache/backends/memory.py

@@ -50,7 +50,7 @@ class MemoryBackend(CacheBackend):
     """
 
     def __init__(self, arguments):
-        self._cache = arguments.pop("cache_dict", {})
+        self._cache = arguments.get("cache_dict", {})
 
     def get(self, key):
         return self._cache.get(key, NO_VALUE)

dogpile/testing/fixtures.py

@@ -50,9 +50,11 @@ def teardown_method(self, method):
     def _check_backend_available(cls, backend):
         pass
 
+    backend: str
     region_args = {}
     config_args = {}
     extra_arguments = {}
+    backend_argument_names = ()
 
     _region_inst = None
     _backend_inst = None
@@ -398,6 +400,33 @@ def boom():
             Exception, "boom", reg.get_or_create, some_key, boom
         )
 
+    def test_argument_dictionary_unmodified(self):
+        fixed_arg_names = getattr(self, "backend_argument_names", None)
+
+        backend_arguments = {}
+        if not fixed_arg_names:
+            backend_arguments.update(self.config_args["arguments"])
+        else:
+            backend_arguments.update(
+                {key: "somevalue" for key in self.backend_argument_names}
+            )
+
+        assert backend_arguments, (
+            "suite has no config_args['arguments'] and no "
+            "backend_argument_names attribute I can use to generate an "
+            "arg dict"
+        )
+
+        backend_arguments.update(
+            {"arbitrary_arg_one": "foo", "arbitrary_arg_two": "bar"}
+        )
+        argument_dict_copy = dict(backend_arguments)
+
+        region = CacheRegion()
+        region.configure(self.backend, arguments=backend_arguments)
+
+        eq_(backend_arguments, argument_dict_copy)
+
 
 def raise_cant_deserialize_exception(v):
     raise CantDeserializeException()

tests/cache/test_memory_backend.py

@@ -4,6 +4,7 @@
 
 class MemoryBackendTest(_GenericBackendTestSuite):
     backend = "dogpile.cache.memory"
+    backend_argument_names = ["cache_dict"]
 
 
 class MemoryBackendSerializerTest(
@@ -12,5 +13,5 @@ class MemoryBackendSerializerTest(
     pass
 
 
-class MemoryPickleBackendTest(_GenericBackendTestSuite):
+class MemoryPickleBackendTest(MemoryBackendTest):
     backend = "dogpile.cache.memory_pickle"