Fix code incompatibilities with Python 2

There are some functionalities used that don't work with Python 2.
- Format strings
- list.clear()
- Type hints
- super() without arguments
- Packages without __init__.py file
- Some import names (futures.thread -> concurrent.futures)

Import behaviour changed between Py2 and 3 and one file was missing
`from __future__ import absolute_import` line (that makes
the behaviour consistent between 2 and 3) which caused import error.

Some members in "c_sharding_info.pyx" had "str" type. This type maps to
"str" both in Py2 and 3 - and those are different types - raw bytes in Py2,
unicode string in py3. This caused errors in Py2, because code was trying
to assign unicode strings to those members.
The fix is to use Cython's / Pyrex's "unicode" type - it maps to
"unicode" in Py2 and to "str" in Py3.

This commit fixes all of those problems.

Author: Lorak-mmk

cassandra/c_shard_info.pyx

@@ -19,8 +19,8 @@ cdef extern from *:
 
 cdef class ShardingInfo():
     cdef readonly int shards_count
-    cdef readonly str partitioner
-    cdef readonly str sharding_algorithm
+    cdef readonly unicode partitioner
+    cdef readonly unicode sharding_algorithm
     cdef readonly int sharding_ignore_msb
     cdef readonly int shard_aware_port
     cdef readonly int shard_aware_port_ssl

cassandra/connection.py

@@ -903,7 +903,7 @@ def _initiate_connection(self, sockaddr):
                     break
                 except Exception as ex:
                     log.debug("port=%d couldn't bind cause: %s", port, str(ex))
-            log.debug(f'connection (%r) port=%d should be shard_id=%d', id(self), port, port % self.total_shards)
+            log.debug('connection (%r) port=%d should be shard_id=%d', id(self), port, port % self.total_shards)
 
         self._socket.connect(sockaddr)
 

cassandra/pool.py

@@ -15,6 +15,8 @@
 """
 Connection pooling and host management.
 """
+from __future__ import absolute_import
+
 from concurrent.futures import Future
 from functools import total_ordering
 import logging
@@ -1200,7 +1202,9 @@ def shutdown(self):
         with self._lock:
             connections_to_close.extend(self._connections)
             self.open_count -= len(self._connections)
-            self._connections.clear()
+            # After dropping support for Python 2 we can again use list.clear()
+            # self._connections.clear()
+            del self._connections[:]
             connections_to_close.extend(self._trash)
             self._trash.clear()
 

cassandra/scylla/__init__.py

@@ -52,12 +52,14 @@ def nth(iterable, n, default=None):
 
 
 class CloudConfiguration:
-    endpoint_factory: SniEndPointFactory
-    contact_points: list
-    auth_provider: AuthProvider = None
-    ssl_options: dict
-    ssl_context: SSLContext
-    skip_tls_verify: bool
+    # Commented out because this syntax doesn't work with Python2
+    # Can be restores after dropping support for Python2
+    # endpoint_factory: SniEndPointFactory
+    # contact_points: list
+    # auth_provider: AuthProvider = None
+    # ssl_options: dict
+    # ssl_context: SSLContext
+    # skip_tls_verify: bool
 
     def __init__(self, configuration_file, pyopenssl=False, endpoint_factory=None):
         cloud_config = yaml.safe_load(open(configuration_file))

cassandra/scylla/cloud.py

@@ -283,7 +283,7 @@ class MockSession(MagicMock):
             keyspace = "reprospace"
 
             def __init__(self, *args, **kwargs):
-                super().__init__(*args, **kwargs)
+                super(MockSession, self).__init__(*args, **kwargs)
                 self.cluster = MagicMock()
                 self.cluster.executor = ThreadPoolExecutor(max_workers=2, initializer=self.executor_init)
                 self.cluster.signal_connection_failure = lambda *args, **kwargs: False

tests/unit/test_host_connection_pool.py

@@ -18,8 +18,8 @@
     import unittest  # noqa
 
 import logging
-from unittest.mock import MagicMock
-from futures.thread import ThreadPoolExecutor
+from mock import MagicMock
+from concurrent.futures import ThreadPoolExecutor
 
 from cassandra.cluster import ShardAwareOptions
 from cassandra.pool import HostConnection, HostDistance
@@ -62,7 +62,7 @@ class MockSession(MagicMock):
             keyspace = "ks1"
 
             def __init__(self, is_ssl=False, *args, **kwargs):
-                super().__init__(*args, **kwargs)
+                super(MockSession, self).__init__(*args, **kwargs)
                 self.cluster = MagicMock()
                 if is_ssl:
                     self.cluster.ssl_options = {'some_ssl_options': True}