A module to generate shorter UUID encodings

src/calibre/utils/short_uuid.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python2
+# vim:fileencoding=utf-8
+# License: GPLv3 Copyright: 2015, Kovid Goyal <kovid at kovidgoyal.net>
+
+from __future__ import (unicode_literals, division, absolute_import,
+                        print_function)
+
+'''
+Generate UUID encoded using a user specified alphabet.
+'''
+
+import string, math, uuid as _uuid
+
+def num_to_string(number, alphabet, alphabet_len, pad_to_length=None):
+    ans = []
+    number = max(0, number)
+    while number:
+        number, digit = divmod(number, alphabet_len)
+        ans.append(alphabet[digit])
+    if pad_to_length is not None and pad_to_length > len(ans):
+        ans.append(alphabet[0] * (pad_to_length - len(ans)))
+    return ''.join(ans)
+
+def string_to_num(string, alphabet_map, alphabet_len):
+    ans = 0
+    for char in reversed(string):
+        ans = ans * alphabet_len + alphabet_map[char]
+    return ans
+
+class ShortUUID(object):
+
+    def __init__(self, alphabet=None):
+        # We do not include zero and one in the default alphabet as they can be
+        # confused with the letters O and I in some fonts. And removing them
+        # does not change the uuid_pad_len.
+        self.alphabet = tuple(sorted(type('')(alphabet or (string.digits + string.ascii_letters)[2:])))
+        self.alphabet_len = len(self.alphabet)
+        self.alphabet_map = {c:i for i, c in enumerate(self.alphabet)}
+        self.uuid_pad_len = int(math.ceil(math.log(1 << 128, self.alphabet_len)))
+
+    def uuid4(self, pad_to_length=None):
+        if pad_to_length is None:
+            pad_to_length = self.uuid_pad_len
+        return num_to_string(_uuid.uuid4().int, self.alphabet, self.alphabet_len, pad_to_length)
+
+    def uuid5(self, namespace, name, pad_to_length=None):
+        if pad_to_length is None:
+            pad_to_length = self.uuid_pad_len
+        return num_to_string(_uuid.uuid5(namespace, name).int, self.alphabet, self.alphabet_len, pad_to_length)
+
+    def decode(self, encoded):
+        return _uuid.UUID(int=string_to_num(encoded, self.alphabet_map, self.alphabet_len))
+
+_global_instance = ShortUUID()
+uuid4 = _global_instance.uuid4
+uuid5 = _global_instance.uuid5
+decode = _global_instance.decode