Fixing flake8 warnings and errors

flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics --exclude benchmark

Excluding the benchmark directory (due to protobuf generated files)
Also removing some Python2 specific code

examples/calculator_client.py

@@ -2,7 +2,6 @@
 
 from __future__ import print_function
 import argparse
-import socket
 import capnp
 
 import calculator_capnp
@@ -302,5 +301,6 @@ def main(host):
 
     print("PASS")
 
+
 if __name__ == '__main__':
     main(parse_args().host)