Disable the serial console, make clean connection and python code will run fater
http://forum.arduino.cc/index.php?topic=191820.msg1421548#msg1421548
https://forum.openwrt.org/viewtopic.php?id=15165
The catch of disabled serial console (device debugging and recovering impossible)
http://forum.arduino.cc/index.php?topic=191820.msg1425151#msg1425151
http://forum.arduino.cc/index.php?topic=191820.msg1480507#msg1480507
http://forum.arduino.cc/index.php?topic=191820.msg1424302#msg1424302
The work around:
http://forum.arduino.cc/index.php?topic=191820.msg1679588#msg1679588