这个答案在本质上与道格拉斯·里德（Douglas Leeder）的相似，但有以下变化：
import string
ALPHABET = string.ascii_uppercase + string.ascii_lowercase + \
string.digits + '-_'
ALPHABET_REVERSE = dict((c, i) for (i, c) in enumerate(ALPHABET))
BASE = len(ALPHABET)
SIGN_CHARACTER = '$'
def num_encode(n):
if n < 0:
return SIGN_CHARACTER + num_encode(-n)
s = []
while True:
n, r = divmod(n, BASE)
s.append(ALPHABET[r])
if n == 0: break
return ''.join(reversed(s))
def num_decode(s):
if s[0] == SIGN_CHARACTER:
return -num_decode(s[1:])
n = 0
for c in s:
n = n * BASE + ALPHABET_REVERSE[c]
return n
>>> num_encode(0)
'A'
>>> num_encode(64)
'BA'
>>> num_encode(-(64**5-1))
'$_____'
一些注意事项：
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