Question

I tried to make a short program that works out the famous Drake equation. I got it to accept integer inputs, decimal inputs, and fractional inputs. However, I get this error when the program attempts to multiply them (right after I input all necessary values the error happens):

Traceback (most recent call last)
  File "C:/Users/Family/Desktop/Programming/Python Files/1/DrakeEquation1.py", line 24, in <module>
    calc() #cal calc to execute it
  File "C:/Users/Family/Desktop/Programming/Python Files/1/DrakeEquation1.py", line 17, in calc
    calc = r*fp*ne*fl*fi*fc*l
TypeError: can't multiply sequence by non-int of type 'str'

My code is as follows:

def intro():
    print('This program will evaluate the Drake equation with your values')

def calc():
    print('What is the average rate of star formation in the galaxy?')
    r = input()
    print('What fraction the stars have planets?')
    fp = input()
    ne = int(input('What is the average number of life supporting planets (per     star)?'))
    print('What fraction of these panets actually develop life')
    fl = input()
    print('What fraction of them will develop intelligent life')
    fi = input()
    print('What fraction of these civilizations have developed detectable technology?')
    fc = input()
    l = int(input('How long will these civilizations release detectable signals?'))
    calc = r*fp*ne*fl*fi*fc*l

    print('My estimate of the number of detectable civilizations is ' + calc + ' .')


if __name__=="__main__":
    intro() #cal intro to execute it 
    calc() #cal calc to execute it 

What do I need to change in order to fix this problem?

Answer 1

You need to convert your input values to floats.

r = float(input())

(Note: in Python versions less than 3, use raw_input instead of input.)

And so on for the other variables. Otherwise you’re attempting to multiply a string by a string.

Edit: as others have pointed out, calc additionally cannot be concatenated to the surrounding strings using the + operator. Use string substitution for that:

print('My estimate of the number of detectable civilizations is %s.' % calc)