How to use a for loop with input function

Question

I simply have to make a sum of three numbers and calculate the average

import sys
sums=0.0
k=3
for w in range(k):
    sums = sums + input("Pleas input number " + str(w+1) + " ")
print("the media is " + str(sums/k) + " and the Sum is " + str(sums))

And the error :

Pleas input number 1 1
Traceback (most recent call last):
  File "/home/user/Python/sec001.py", line 5, in <module>
    sums = sums + input("Pleas input number " + str(w+1) + " ");
TypeError: unsupported operand type(s) for +: 'float' and 'str'

Think of the type of the value returned by input(..) by trying type(input("> ")) in your console; you'll see it is of type str. Can a str be added to a float (sums) without first being converted? — Dimitris Fasarakis Hilliard
– Dimitris Fasarakis Hilliard, Commented Nov 3, 2016 at 14:30

MichaelMMeskhi · Accepted Answer · 2016-11-03 14:48:00Z

3

Why not do the simple version then optimize it?

def sum_list(l):
    sum = 0
    for x in l:
        sum += x
    return sum

l = list(map(int, input("Enter numbers separated by spaces:  ").split())) 
sum_list(l)

Your problem was that you were not casting your input from 'str' to 'int'. Remember, Python auto-initializes data types. Therefore, explicit casting is required. Correct me if I am wrong, but that's how I see it.

Hope I helped :)

edited Nov 3, 2016 at 14:48

answered Nov 3, 2016 at 14:44

MichaelMMeskhi

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7 Comments

OneCricketeer Over a year ago

Why not optimize your code to use Python's built in sum function?

MichaelMMeskhi Over a year ago

You are correct! Beg my pardon, but why have you edited the parameter list to 'l' instead of 'n'. If 'l' is to be used then all changes must be made.

MichaelMMeskhi Over a year ago

My bad I have made a mistake :)

OneCricketeer Over a year ago

Your loop has for x in l. I fixed it

MichaelMMeskhi Over a year ago

Thank you. Silly mistakes kill me :\

|

BernardoGO · Accepted Answer · 2016-11-03 14:51:07Z

The input() function returns a string(str) and Python does not convert it to float/integer automatically. All you need to do is to convert it.

import sys;
sums=0.0;
k=3;
for w in range(k):
    sums = sums + float(input("Pleas input number " + str(w+1) + " "));
print("the media is " + str(sums/k) + " and the Sum is " + str(sums));

If you want to make it even better, you can use try/except to deal with invalid inputs. Also, import sys is not needed and you should avoid using semicolon.

sums=0.0
k=3
for w in range(k):
    try:
        sums = sums + float(input("Pleas input number " + str(w+1) + " "))
    except ValueError:
        print("Invalid Input")
print("the media is " + str(sums/k) + " and the Sum is " + str(sums))

tdelaney · Accepted Answer · 2016-11-03 14:44:15Z

1

input returns a string and you need to create an int or float from that. You also have to deal with the fact that users can't follow simple instructions. Finally, you need to get rid of those semicolons - they are dangerous and create a hostile work environment (at least when you bump into other python programmers...!)

import sys
sums=0.0
k=3
for w in range(k):
    while True:
        try:
            sums += float(input("Pleas input number " + str(w+1) + " "))
            break
        except ValueError:
            print("That was not a number")
print("the media is " + str(sums/k) + " and the Sum is " + str(sums))

answered Nov 3, 2016 at 14:44

tdelaney

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