Question

I’ve got a Perl function which takes a timestamp and returns either the unchanged timestamp (if it’s never seen it before) or otherwise, it appends some letters to make it unique:

sub uniqify($) {   my $timestamp = shift;    state $last_ts = -1;   state $next_letter = 'A';    if ($timestamp == $last_ts) {     $timestamp .= $next_letter++;   } else {     $last_ts = $timestamp;     $next_letter = 'A';   }    return $timestamp; } 

So if you call it four times, with the values 1, 1, 1, and 2, it will return 1, then 1A, then 1B, then 2.

Note: It only ever gets called with ever-increasing timestamps, so it doesn’t need to recall every one it’s ever seen, just the last one.

Now I need to translate this function to Python. I’ve learned that I can replace the ‘state’ variables with globals (yuck!) or perhaps attach them to the function as attributes, but neither of those is particularly elegant.

Also, Python doesn’t have something like Perl’s magic autoincrement, where if you ‘++’ a variable whose value is ‘A’, it becomes ‘B’ — or if it’s ‘Z’, it becomes ‘AA’. So that’s a curveball too.

I’m hacking together a solution, but it’s really ugly and hard to read. Translating from Perl to Python is supposed to have the opposite effect, right? 🙂 So I’m offering this as a challenge to SO users. Can you make it an elegant Python function?

Answer 1

Look at this answer for a robust method to convert a number to an alphanumeric id

The code I present doesn’t go from ‘Z’ to ‘AA’, instead goes to ‘BA’, but I suppose that doesn’t matter, it still produces a unique id

from string import uppercase as up import itertools  def to_base(q, alphabet):     if q < 0: raise ValueError( 'must supply a positive integer' )     l = len(alphabet)     converted = []     while q != 0:         q, r = divmod(q, l)         converted.insert(0, alphabet[r])     return ''.join(converted) or alphabet[0]  class TimestampUniqifier( object ):     def __init__(self):         self.last = ''         self.counter = itertools.count()     def __call__( self, str ):         if str == self.last:             suf = self.counter.next()             return str + to_base( suf, up )         else:             self.last = str             self.counter = itertools.count()             return str              timestamp_uniqify = TimestampUniqifier() 

usage:

timestamp_uniqify('1') '1' timestamp_uniqify('1') '1A' timestamp_uniqify('1') '1B' timestamp_uniqify('1') '1C' timestamp_uniqify('2') '2' timestamp_uniqify('3') '3' timestamp_uniqify('3') '3A' timestamp_uniqify('3') '3B' 

You can call it maaaany times and it will still produce good results:

for i in range(100): print timestamp_uniqify('4')  4 4A 4B 4C 4D 4E 4F 4G 4H 4I 4J 4K 4L 4M 4N 4O 4P 4Q 4R 4S 4T 4U 4V 4W 4X 4Y 4Z 4BA 4BB 4BC 4BD 4BE 4BF 4BG 4BH 4BI 4BJ 4BK 4BL 4BM 4BN 4BO 4BP 4BQ 4BR 4BS 4BT 4BU 4BV 4BW 4BX 4BY 4BZ 4CA 4CB 4CC 4CD 4CE 4CF 4CG 4CH 4CI 4CJ 4CK 4CL 4CM 4CN 4CO 4CP 4CQ 4CR 4CS 4CT 4CU 4CV 4CW 4CX 4CY 4CZ 4DA 4DB 4DC 4DD 4DE 4DF 4DG 4DH 4DI 4DJ 4DK 4DL 4DM 4DN 4DO 4DP 4DQ 4DR 4DS 4DT 4DU