Warn when doing O(n) operations on RedisLists (#511)

* Warn when doing O(n) operations on RedisLists

* Silence all Pottery warnings during unit test runs

* Bump version number

pottery/__init__.py

@@ -30,7 +30,7 @@
 
 
 __title__ = 'pottery'
-__version__ = '2.0.0'
+__version__ = '2.0.1'
 __description__ = __doc__.split(sep='\n\n', maxsplit=1)[0]
 __url__ = 'https://github.com/brainix/pottery'
 __author__ = 'Rajiv Bakulesh Shah'
@@ -49,6 +49,8 @@
 from .exceptions import TooManyExtensions  # isort:skip
 from .exceptions import ExtendUnlockedLock  # isort:skip
 from .exceptions import ReleaseUnlockedLock  # isort:skip
+from .exceptions import PotteryWarning  # isort:skip
+from .exceptions import InefficientAccessWarning  # isort:skip
 
 from .bloom import BloomFilter  # isort:skip
 from .cache import CachedOrderedDict  # isort:skip
@@ -76,6 +78,8 @@
     'TooManyExtensions',
     'ExtendUnlockedLock',
     'ReleaseUnlockedLock',
+    'PotteryWarning',
+    'InefficientAccessWarning',
 
     'BloomFilter',
     'CachedOrderedDict',

pottery/exceptions.py

@@ -95,3 +95,10 @@ class ReleaseUnlockedLock(PrimitiveError, RuntimeError):
 
 class QuorumIsImpossible(PrimitiveError, RuntimeError):
     'Too many Redis masters threw RedisErrors; quorum can not be achieved.'
+
+
+class PotteryWarning(Warning):
+    'Base warning class for Pottery containers.'
+
+class InefficientAccessWarning(PotteryWarning):
+    'Doing an O(n) Redis operation.'

pottery/list.py

@@ -20,6 +20,7 @@
 import functools
 import itertools
 import uuid
+import warnings
 from typing import Any
 from typing import Callable
 from typing import Iterable
@@ -35,6 +36,7 @@
 from .annotations import F
 from .base import Base
 from .base import JSONTypes
+from .exceptions import InefficientAccessWarning
 from .exceptions import KeyExistsError
 
 
@@ -124,8 +126,12 @@ def __getitem__(self, index: Union[slice, int]) -> Any:
     @_raise_on_error
     def __setitem__(self, index: int, value: JSONTypes) -> None:  # type: ignore
         'l.__setitem__(index, value) <==> l[index] = value.  O(n)'
-        if isinstance(index, slice):
-            with self._watch() as pipeline:
+        with self._watch() as pipeline:
+            if isinstance(index, slice):
+                warnings.warn(
+                    cast(str, InefficientAccessWarning.__doc__),
+                    InefficientAccessWarning,
+                )
                 encoded_values = [self._encode(value) for value in value]
                 indices = self.__slice_to_indices(index)
                 pipeline.multi()
@@ -137,9 +143,16 @@ def __setitem__(self, index: int, value: JSONTypes) -> None:  # type: ignore
                     num += 1
                 if num:
                     pipeline.lrem(self.key, num, 0)
-        else:
-            index = self.__slice_to_indices(index).start
-            self.redis.lset(self.key, index, self._encode(value))
+            else:
+                index = self.__slice_to_indices(index).start
+                len_ = cast(int, pipeline.llen(self.key))
+                if index not in {-1, 0, len_-1}:
+                    warnings.warn(
+                        cast(str, InefficientAccessWarning.__doc__),
+                        InefficientAccessWarning,
+                    )
+                pipeline.multi()
+                pipeline.lset(self.key, index, self._encode(value))
 
     @_raise_on_error
     def __delitem__(self, index: Union[slice, int]) -> None:  # type: ignore
@@ -156,6 +169,10 @@ def __delete(self, pipeline: Pipeline, index: Union[slice, int]) -> None:
         # to set l[index] to a UUID4, then to delete the value UUID4.  More
         # info:
         #   http://redis.io/commands/lrem
+        warnings.warn(
+            cast(str, InefficientAccessWarning.__doc__),
+            InefficientAccessWarning,
+        )
         indices, num = self.__slice_to_indices(index), 0
         uuid4 = str(uuid.uuid4())
         pipeline.multi()
@@ -190,6 +207,10 @@ def _insert(self,
             # UUID4, then to set the value UUID4 back to the original pivot
             # pivot value.  More info:
             #   http://redis.io/commands/linsert
+            warnings.warn(
+                cast(str, InefficientAccessWarning.__doc__),
+                InefficientAccessWarning,
+            )
             uuid4 = str(uuid.uuid4())
             pivot = cast(bytes, pipeline.lindex(self.key, index))
             pipeline.multi()

tests/base.py

@@ -21,16 +21,20 @@
 import random
 import sys
 import unittest
+import warnings
 from typing import NoReturn
 
 from redis import Redis
 
+from pottery import PotteryWarning
+
 
 class TestCase(unittest.TestCase):
     @classmethod
     def setUpClass(cls) -> None:
         logger = logging.getLogger('pottery')
         logger.setLevel(logging.CRITICAL)
+        warnings.filterwarnings('ignore', category=PotteryWarning)
 
     def setUp(self) -> None:
         super().setUp()