1、打开PYTHON，新建一个PY文档。
2、num = input("Please input whatever number you want: ")荏鱿胫协num_double = num * 2print(num)print(num_double)如果只用input，那么如果想要做运算，直接做运算的话只会重复数字，因为input里面只是字符串。
3、num = int(input猾诮沓靥("Please input whatever number you want: "))num_double = num * 2print(num)print(num_double)如果在前面加上int，那么就可以把字符串定义为整型，这样就可以做运算了。
4、num = float(input("Please input whatever number you want: "))num_double = num * 2print(num)print(num_double)除了整型，还可以定义为浮点型，就会有小数点。
5、num = eval(input("Please input whatever number you want: "))num_double = num * 2print(num)print(num_double)如果用eval，这样就可以直接做运算。
6、num = eval(input("Please input whatever number you want: "))num_double = num * 2print(num)print(num_double)当然如果你输入浮点型，经过eval后也是会变为浮点型。
