在python中，怎么将字符串类型的变量强制转换成float类型的变量

Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:01:18) [MSC v.1900 32 bit (Intel)] on win32Type "help", "copyright", "credits" or "license" for more information.>>> s = '123.4'>>> float(