TypeError: unsupported operand type(s) for /: 'NoneType' and 'float'

Traceback (most recent call last):
File “xxxxx.py”, line 16, in
print (float(a) - 0.01) / main_std
TypeError: unsupported operand type(s) for /: ‘NoneType’ and ‘float’

Reason:
缺少括号。在python3中 print输出的语句需要使用括号()，如print(‘string’)

Solution:
print ((float(a) - 0.01) / main_std)