Fix default value of max_workers

pyathena/async_cursor.py

@@ -2,7 +2,6 @@
 from __future__ import absolute_import
 from __future__ import unicode_literals
 import logging
-import os
 
 from concurrent.futures.thread import ThreadPoolExecutor
 
@@ -11,6 +10,12 @@
 from pyathena.error import ProgrammingError, NotSupportedError
 from pyathena.result_set import AthenaResultSet
 
+try:
+    from multiprocessing import cpu_count
+except ImportError:
+    def cpu_count():
+        return None
+
 
 _logger = logging.getLogger(__name__)
 
@@ -21,7 +26,7 @@ def __init__(self, client, s3_staging_dir, schema_name, poll_interval,
                  encryption_option, kms_key, converter, formatter,
                  retry_exceptions, retry_attempt, retry_multiplier,
                  retry_max_delay, retry_exponential_base,
-                 max_workers=(os.cpu_count() or 1) * 5,
+                 max_workers=(cpu_count() or 1) * 5,
                  arraysize=CursorIterator.DEFAULT_FETCH_SIZE):
         super(AsyncCursor, self).__init__(client, s3_staging_dir, schema_name, poll_interval,
                                           encryption_option, kms_key, converter, formatter,