代码如下：

import time
import datetime

# 时间字符串加8小时
timestring = time.time() #获取当前时间戳
timestamp = float(int(timestring)) #转换为float格式

print (timestamp)  # 1576422806.0
print (type(timestamp))  # <class 'float'>

datetime_struct = datetime.datetime.fromtimestamp(timestamp)
print (type(datetime_struct))  # <type 'datetime.datetime'>

datetime_obj = (datetime_struct - datetime.timedelta(hours=8))
print (datetime_obj)  # 时间减去8小时：2019-12-15 15:13:26  <type 'datetime.datetime'>

datetime_str = datetime_obj.strftime('%Y-%m-%d %H:%M:%S')
print (datetime_str)  # 2019-12-15 15:13:26  <type 'str'>