Fastest way to insert these dashes in python string?

Question

So I know Python strings are immutable, but I have a string:

c[\'date\'] = \"20110104\"

Which I would like to convert to

c[\'da         


        

Answer 1

s = '20110104'


def option_1():
    return '-'.join([s[:4], s[4:6], s[6:]])

def option_1a():
    return '-'.join((s[:4], s[4:6], s[6:]))

def option_2():
    return '{}-{}-{}'.format(s[:4], s[4:6], s[6:])

def option_3():
    return '%s-%s-%s' % (s[:4], s[4:6], s[6:])

def option_original():
    return s[:4] + "-" + s[4:6] + "-" + s[6:]

Running %timeit on each yields these results

• option_1: 35.9 ns per loop
• option_1a: 35.8 ns per loop
• option_2: 36 ns per loop
• option_3: 35.8 ns per loop
• option_original: 36 ns per loop

So... pick the most readable because the performance improvements are marginal