Code review time… In a conversation about URL shorteners and “Coke Rewards” realized that there was a case where I needed to be able to generate safe character strings that had high reliability for input back by human beings. The typical Base62 systems where there is ambiguity between (O, o and 0) make things hard (along with all of those upper vs. lower case cases).
Here’s the quick module I put together that is a safe base converter to human readable numbers.
import types
class BaseConverter(object):
""" Convert a number between two bases of digits, by default it's a human safe set
>>> v = BaseConverter(BaseConverter.BASE10)
>>> v.to_decimal(22)
22
>>> v.from_decimal(22)
'22'
>>> v = BaseConverter(BaseConverter.BASE2)
>>> v.to_decimal(22)
Traceback (most recent call last):
...
ValueError: character '2' not in base
>>> v.to_decimal(10)
2
>>> v.to_decimal('10')
2
>>> v.from_decimal(22)
'10110'
>>> v = BaseConverter()
>>> v.to_decimal(22)
58
>>> v.from_decimal(123123)
'5h17'
>>> v.to_decimal('5H17')
123123
>>> v = BaseConverter(BaseConverter.BASE62)
>>> v.from_decimal(257938572394L)
'4XYBxik'
>>> v.to_decimal('4XYBxik')
257938572394
>>> v = BaseConverter((('Zero ',),('One ',)))
>>> v.from_decimal(BaseConverter(BaseConverter.BASE2).to_decimal('1101'))
'One One Zero One '
"""
HUMAN_TABLE = (
('0','O','o','Q','q'),
('1','I','i','L','l','J','j'),
('2','Z','z'),
('3',),
('4',),
('5','S','s'),
('6',),
('7',),
('8',),
('9',),
('a','A',),
('b','B',),
('c','C',),
('d','D',),
('e','E',),
('f','F',),
('g','G',),
('h','H',),
('k','K',),
('m','M',),
('n','N',),
('p','P',),
('r','R',),
('t','T',),
('u','U','V','v'),
('w','W',),
('x','X',),
('y','Y',),
)
BASE2 = "01"
BASE10 = "0123456789"
BASE62 = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
BASE16 = (
('0',),
('1',),
('2',),
('3',),
('4',),
('5',),
('6',),
('7',),
('8',),
('9',),
('A','a',),
('B','b',),
('C','c',),
('D','d',),
('E','e',),
('F','f',),
)
def __init__(self, digitset=HUMAN_TABLE):
if type(digitset) in (types.StringType, types.UnicodeType) :
self.digitset = [(v) for v in digitset]
else :
self.digitset = digitset
self.base = len(self.digitset)
self.output_map = {}
self.output_digits = [v[0] for v in self.digitset]
self.input_set = {}
for idx, l in enumerate(self.digitset) :
for k in l :
self.input_set[k] = idx
#print 'OUT DIGITS', self.output_digits
#print 'INPUT SET', self.input_set
def from_decimal(self, i):
return self.convert(i, self.BASE10, self.output_digits)
def to_decimal(self, s):
return int(self.convert(s, self.input_set, self.BASE10))
def convert(self, number, fromdigits, todigits) :
fd = fromdigits
fbase = self.base
if type(fromdigits) in (types.StringType, types.UnicodeType) :
fbase = len(fromdigits)
fd = dict([(fromdigits[idx], idx) for idx in range(0,len(fromdigits))])
return self._convert(number, fbase, fd, todigits)
@staticmethod
def _convert(number, fbase, fromdigits, todigits) :
# Based on http://code.activestate.com/recipes/111286/
number = str(number)
if number[0] == '-':
number = number[1:]
neg = 1
else:
neg = 0
# make an integer out of the number
x = 0
#print "fbase = ", len(fromdigits)
for digit in number :
try :
x = x * fbase + fromdigits[digit]
except KeyError, e:
raise ValueError("character '%s' not in base" % digit)
# create the result in base 'len(todigits)'
tbase = len(todigits)
if x == 0:
res = todigits[0]
else:
res = ""
while x > 0:
#print "divmod(%d, %d) = %r" % (x, tbase, divmod(x,tbase))
x, digit = divmod(x, tbase)
res = todigits[digit] + res
if neg:
res = '-' + res
return res
binary = BaseConverter(BaseConverter.BASE2)
hex = BaseConverter(BaseConverter.BASE16)
base62 = BaseConverter(BaseConverter.BASE62)
human = BaseConverter()
if __name__ == '__main__' :
import doctest
import random
doctest.testmod()
