Removing first character from string

Question

I am working on a CodeEval challenge and have a solution to a problem which takes a list of numbers as an input and then outputs the sum of the digits of each line. Here is my code to make certain you understand what I mean:

import sys
test_cases = open(sys.argv[1], 'r')
for test in test_cases:
    if test:
        num = int(test)
        total =0
        while num != 0:
            total += num % 10
            num /= 10
        print total


test_cases.close()

I am attempting to rewrite this where it takes the number as a string, slices each 0-index, and then adds those together (curious to see what the time and memory differences are - totally new to coding and trying to find multiple ways to do things as well)

However, I am stuck on getting this to execute and have the following:

import sys
test_cases = open(sys.argv[1], 'r')
for test in test_cases:
    sums = 0
    while test:
      sums = sums + int(str(test)[0])
      test = test[1:]
    print sums

test_cases.close()

I am receiving a "ValueError: invalid literal for int() with base 10: ''"

The sample input is a text file which looks like this:

3011
6890
8778
1844
42
8849
3847
8985
5048
7350
8121
5421
7026
4246
4439
6993
4761
3658
6049
1177

Thanks for any help you can offer!

Answer 1

Your issue is the newlines (eg. /n or /r/n) at the end of each line.

Change this line:

for test in test_cases:

into this to split out the newlines:

for test in test_cases.read().splitlines():

Answer 2

try this code:

tot = 0
with open(sys.argv[1], 'r') as f:
    for line in f:
        try:
            tot += int(line)
        except ValueError:
            print "Not a number"

print tot

• using the context manager ( with... ) the file is automatically closed.
• casting to int filter any empty or not valid value

you can substitute print with any other statement optimal for you ( raise or pass depending on your goals)