Making string series in Python

Question

I have a problem in Python I simply can't wrap my head around, even though it's fairly simple (I think).

I'm trying to make "string series". I don't really know what it's called, but it goes like this:

I want a function that makes strings that run in series, so that every time the functions get called it "counts" up once.

I have a list with "a-z0-9._-" (a to z, 0 to 9, dot, underscore, dash). And the first string I should receive from my method is aaaa, next time I call it, it should return aaab, next time aaac etc. until I reach ----

Also the length of the string is fixed for the script, but should be fairly easy to change.

(Before you look at my code, I would like to apologize if my code doesn't adhere to conventions; I started coding Python some days ago so I'm still a noob).

What I've got:

Generating my list of available characters

chars = []
for i in range(26):
    chars.append(str(chr(i + 97)))

for i in range(10):
    chars.append(str(i))

chars.append('.')
chars.append('_')
chars.append('-')

Getting the next string in the sequence

iterationCount = 0
nameLen = 3
charCounter = 1
def getString():
    global charCounter, iterationCount
    name = ''
    for i in range(nameLen):
        name += chars[((charCounter + (iterationCount % (nameLen - i) )) % len(chars))]
    charCounter += 1
    iterationCount += 1
    return name

And it's the getString() function that needs to be fixed, specifically the way name gets build.

I have this feeling that it's possible by using the right "modulu hack" in the index, but I can't make it work as intended!

That's definately fix my iteration problem. But the problem is how to actually generate the strings :) — f2lollpll
– f2lollpll, Commented Apr 25, 2013 at 21:06
@mata beat me too it. I was going to say you will be amazed at how easy the solution will be. — dansalmo
– dansalmo, Commented Apr 25, 2013 at 21:13

mata · Accepted Answer · 2013-04-25 21:20:24Z

8

What you try to do can be done very easily using generators and itertools.product:

import itertools

def getString(length=4, characters='abcdefghijklmnopqrstuvwxyz0123456789._-'):
    for s in itertools.product(characters, repeat=length):
        yield ''.join(s)

for s in getString():
    print(s)


aaaa
aaab
aaac
aaad
aaae
aaaf
...

edited Apr 25, 2013 at 21:20

answered Apr 25, 2013 at 21:09

mata

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4 Comments

dansalmo Over a year ago

Since it is a generator, it will automatically stop when it gets to the end of the itertools.product sequence.

Jon Clements Over a year ago

Would be better to call len - length so as to not shadow the builtin, and itertools.product(*([characters]*len)) seems a bit convoluted - I would suggest itertools.product(characters, repeat=length)

mata Over a year ago

@JonClements - you're right :) pydoc itertools.product doesn't mention the repeat keyword argument (at least not right on top)

f2lollpll Over a year ago

As they write in the tutorial; "Batteries included". This was the exact answer I was looking for :) Thanks mata! That was awesome.. Once again SO is a dazzeling magical place for knowledge.

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