negative number problem

[aLiase]

so heres my code

input = open('DATA1.txt', 'r')
output = open('OUT1.txt', 'w')
numbers = input.readlines()
for x in range(1):
    set = numbers[x]
    a = float(set[6])
    b = float(set[4])
    c = float(set[2])
    d = float(set[0])
    r = (a - b)**2 + (c - d)**2
    answer = round(r * 3.14169,3)
    output.writelines('%s\n' % answer)
output.close()
 

and heres what data1.txt has

1.312 2 3 4
 

What my problem is if I change the 1.312 to a negative 1.312 it errors out and gives me

Traceback (most recent call last):
  File "circle.py", line 6, in <module>
    a = float(set[6])
ValueError: empty string for float()
 

It seem to happen to both negative integer and float numbers.

[bvdet]

so heres my code

input = open('DATA1.txt', 'r')
output = open('OUT1.txt', 'w')
numbers = input.readlines()
for x in range(1):
    set = numbers[x]
    a = float(set[6])
    b = float(set[4])
    c = float(set[2])
    d = float(set[0])
    r = (a - b)**2 + (c - d)**2
    answer = round(r * 3.14169,3)
    output.writelines('%s\n' % answer)
output.close()
 

and heres what data1.txt has

1.312 2 3 4
 

What my problem is if I change the 1.312 to a negative 1.312 it errors out and gives me

Traceback (most recent call last):
  File "circle.py", line 6, in <module>
    a = float(set[6])
ValueError: empty string for float()
 

It seem to happen to both negative integer and float numbers.

Don't use set as a variable name because you will mask Python's built in set() function. Let's call it item. item is the first element in a list of one element. You are trying to apply float() to a minus sign because you are slicing the string "-1.312 2 3 4". You should split the string, then process the four numbers in the resulting list.

input = open('data.txt', 'r')
output = open('output.txt', 'w')
numberList = input.readlines()
for item in numberList:
    items = item.split()
    a = float(items[3])
    b = float(items[2])
    c = float(items[1])
    d = float(items[0])
    r = (a - b)**2 + (c - d)**2
    answer = round(r * 3.14169,3)
    output.writelines('%s\n' % answer)
output.close()