Naming a Slice

Problem

• Your program has become an unreadable mess of hardcoded slice indices and you want to clean it up.

Solution

• Use slice()

######    0123456789012345678901234567890123456789012345678901234567890'
record = '....................100          .......513.25     ..........'
cost = int(record[20:32]) * float(record[40:48])
print(cost)

51325.0

SHARES = slice(20,32)
PRICE  = slice(40,48)
cost = int(record[SHARES]) * float(record[PRICE])
print(cost)

51325.0

Why use slice()

• If you have a slice instance s, you can get more information about it by looking at its s.start, s.stop, and s.step attributes, respectively

a = slice(10, 50, 2)
print(a.start)
print(a.stop)
print(a.step)

10
50
2

• In addition, you can map a slice onto a sequence of a specific size by using its indices(size) method.

s = 'HelloWorld'
a = slice(5, 10, 2)
a.indices(len(s))

(5, 10, 2)

for i in range(*a.indices(len(s))):
    print(s[i])

W
r
d