如何根据用户从键盘输入的内容定义公式？ （蟒蛇）

Question

It's my very first question so I hope I'll put it right.

I'm doing some predefined exercises in Python and one request is to define the following formula:

{6*[2+(a-1)%b]*2a} with user's input from the keyboard.

If I am to pick the "a" and "b" my self, the formula is working, however, when ask input from user ( raw_input ) I'm getting an error and I can't figure out why.

The code I tried looks like this:

a = raw_input("enter the first number")
b = raw_input("enter the second number")

print (6*(2+(a-1)%b)*2**a)

And the error message is this:

Traceback (most recent call last):
  File "python", line 4, in <module>
TypeError: unsupported operand type(s) for -: 'unicode' and 'int'

Thank you in advance for your help, Victor

Answer 1

In python2, which you sadly chose to use, the function raw_input returns a string. You must convert it into a number:

a = float(raw_input("enter the first number"))
b = float(raw_input("enter the second number"))

And 2**a probably should be 2*a , unless you raise 2 to power a .