英文文档：
input([prompt])
if the prompt argument is present, it is written to standard output without a trailing newline. the function then reads a line from input, converts it to a string (stripping a trailing newline), and returns that. when eof is read, eoferror is raised
说明：
1. 如果提供了promat参数，首先将参数值输出到标准的输出，并且不换行。函数读取用户输入的值，将其转换成字符串。
>>> s = input(‘please input your name:’)
please input your name:ain>>> s’ain’