Avoid nested import

... to get rid of F401 error by flake8.

tests/test_token_plugins.py

@@ -7,6 +7,11 @@ import unittest
 from unittest.mock import patch, MagicMock
 from jwcrypto import jwt, jwk
 
+try:
+    import redis
+except ImportError:
+    redis = None
+
 from websockify.token_plugins import parse_source_args, ReadOnlyTokenFile, JWTTokenApi, TokenRedis
 
 
@@ -206,9 +211,7 @@ class JWSTokenTestCase(unittest.TestCase):
 
 class TokenRedisTestCase(unittest.TestCase):
     def setUp(self):
-        try:
+        if redis is None:
-            import redis
-        except ImportError:
             patcher = patch.dict(sys.modules, {'redis': MagicMock()})
             patcher.start()
             self.addCleanup(patcher.stop)

websockify/token_plugins.py

@@ -5,6 +5,11 @@ import re
 import json
 from pathlib import Path
 
+try:
+    import redis
+except ImportError:
+    redis = None
+
 logger = logging.getLogger(__name__)
 
 _SOURCE_SPLIT_REGEX = re.compile(
@@ -256,9 +261,7 @@ class TokenRedis(BasePlugin):
           pip install redis
     """
     def __init__(self, src):
-        try:
+        if redis is None:
-            import redis
-        except ImportError:
             logger.error("Unable to load redis module")
             sys.exit()
         # Default values
@@ -314,9 +317,7 @@ class TokenRedis(BasePlugin):
             sys.exit()
 
     def lookup(self, token):
-        try:
+        if redis is None:
-            import redis
-        except ImportError:
             logger.error("package redis not found, are you sure you've installed them correctly?")
             sys.exit()