Convert from numbers to letters

[Steven Bethard]

Gary Wilson Jr wrote:
> Gary Wilson Jr wrote:
> 
>>alpha = 'abcdefghijklmnopqrstuvwxyz'.upper()
>>pairs = [x for x in alpha] + [''.join((x,y)) for x in alpha for y in alpha]
> 
> I forget, is string concatenation with '+' just as fast as join()
> now (because that would look even nicer)?

Certain looping constructs like:

x = ''
for y in z:
     x += y

are now (in CPython 2.4) somewhere near the speed of:

x = []
for y in z:
     x.append(y)
x = ''.join(x)

but this isn't really relevant to your problem because you're only 
joining two characters:

$ python -m timeit -s "import string; a = string.ascii_uppercase" 
"[''.join([x, y]) for x in a for y in a]"
1000 loops, best of 3: 1.02 msec per loop

$ python -m timeit -s "import string; a = string.ascii_uppercase"
"[x + y for x in a for y in a]"
1000 loops, best of 3: 295 usec per loop

Unsurprisingly, it's actually faster to simply concatenate the two 
characters.

STeVe