Make redis dependency optional

CHANGELOG.md

@@ -12,6 +12,10 @@ While this is unreleased, please only add v3 features here. Rebasing master onto
 ### Added
 
 * `Scope` - An enum which contains all of the authorization scopes (see [here](https://github.com/plamere/spotipy/issues/652#issuecomment-797461311)).
+* Added `RedisCacheHandler`, a cache handler that stores the token info in Redis.
+* Added a new parameter to `RedisCacheHandler` to allow custom keys (instead of the default `token_info` key)
+* Simplify check for existing token in `RedisCacheHandler`
+* Make redis an optional dependency
 
 ### Changed
 

README.md

@@ -26,6 +26,12 @@ or upgrade
 pip install spotipy --upgrade
 ```
 
+Spotipy includes optional support for caching Spotify access tokens to a Redis server. To use this support, make sure to specify the `redis` extra:
+
+```bash
+pip install spotipy[redis]
+```
+
 ## Quick Start
 
 A full set of examples can be found in the [online documentation](http://spotipy.readthedocs.org/) and in the [Spotipy examples directory](https://github.com/plamere/spotipy/tree/master/examples).

setup.py

@@ -11,9 +11,15 @@
     'Sphinx>=1.5.2'
 ]
 
+redis_reqs = [
+    "redis>=3.5.3",
+    "redis<4.0.0;python_version<'3.4'",
+]
+
 extra_reqs = {
     'doc': doc_reqs,
-    'test': test_reqs
+    'test': test_reqs,
+    'redis': redis_reqs,
 }
 
 setup(

spotipy/cache_handler.py

@@ -12,8 +12,7 @@
 import os
 from spotipy.util import CLIENT_CREDS_ENV_VARS
 from abc import ABC, abstractmethod
-
-from redis import RedisError
+import warnings
 
 logger = logging.getLogger(__name__)
 
@@ -188,8 +187,19 @@ def __init__(self, redis, key=None):
         self.redis = redis
         self.key = key if key else 'token_info'
 
+        try:
+            from redis import RedisError  # noqa: F401
+        except ImportError:
+            warnings.warn(
+                'Error importing module "redis"; '
+                'it is required for RedisCacheHandler',
+                UserWarning
+            )
+
     def get_cached_token(self):
         token_info = None
+        from redis import RedisError
+
         try:
             token_info = self.redis.get(self.key)
             if token_info:
@@ -200,6 +210,8 @@ def get_cached_token(self):
         return token_info
 
     def save_token_to_cache(self, token_info):
+        from redis import RedisError
+
         try:
             self.redis.set(self.key, json.dumps(token_info))
         except RedisError as e: