Practice python task for exam?

Question

I'm practicing previous python exam question for an upcoming exam but my code is screwy.

1. The task is to make a text file with a list of weights in grams (done).

2. Prompts user for file name, reads the weights, adds them in a list and calculates the total weight.

Herein lies the problem:

try:

   file = input('Enter file name:')

   f = open('weights.txt', 'r')

   sum=0

   for line in f:

      sum = sum+(int(line.strip()))/1000

      print('The textbook weight in kg:', sum)

except:

   print('File cannot be opened')

The output the programme shows is:

"The textbook weight in kg: 0.5

The textbook weight in kg: 0.65

The textbook weight in kg: 1.35

The textbook weight in kg: 1.6500000000000001

The textbook weight in kg: 1.9000000000000001"

But the output i need is:

1.9 only,without the previous lines.

As I'm still a beginner, I know very little about the correct code. So any help will be appreciated

Answer 1

Your problem is with your indentation. You should print your result after the whole for loop is executed, i.e.

try:
    file = input('Enter file name:')
    f = open('weights.txt', 'r')
    sum=0   
    for line in f:
        sum = sum+(int(line.strip()))/1000
    print('The textbook weight in kg:', sum)
except:
    print('File cannot be opened')

Also for the floating point inaccuracy thing, you could format your print like this:

print('The textbook weight in kg:{:.2f}'.format(sum))
# The textbook weight in kg:1.90