old_mnemonic: speed up mn_decode

mn_decode is used by mnemonic.make_seed which now takes around 25% less time

electrum/keystore.py

@@ -904,7 +904,7 @@ def from_seed(seed, passphrase, is_p2sh=False):
             xtype = 'p2wsh' if is_p2sh else 'p2wpkh'
         keystore.add_xprv_from_seed(bip32_seed, xtype, der)
     else:
-        raise BitcoinException('Unexpected seed type {}'.format(t))
+        raise BitcoinException('Unexpected seed type {}'.format(repr(t)))
     return keystore
 
 def from_private_key_list(text):

electrum/old_mnemonic.py

@@ -26,7 +26,7 @@
 
 # list of words from http://en.wiktionary.org/wiki/Wiktionary:Frequency_lists/Contemporary_poetry
 
-words = [
+words = (
 "like",
 "just",
 "love",
@@ -1653,7 +1653,8 @@ words = [
 "unseen",
 "weapon",
 "weary",
-]
+)
+_words_indexes = {w: i for i, w in enumerate(words)}
 
 n = len(words)
 assert n == 1626
@@ -1679,9 +1680,9 @@ def mn_decode( wlist ):
     out = ''
     for i in range(len(wlist)//3):
         word1, word2, word3 = wlist[3*i:3*i+3]
-        w1 =  words.index(word1)
+        w1 =  _words_indexes[word1]
-        w2 = (words.index(word2))%n
+        w2 = (_words_indexes[word2]) % n
-        w3 = (words.index(word3))%n
+        w3 = (_words_indexes[word3]) % n
         x = w1 +n*((w2-w1)%n) +n*n*((w3-w2)%n)
         out += '%08x'%x
     return out

electrum/tests/test_mnemonic.py

@@ -186,5 +186,6 @@ class Test_seeds(ElectrumTestCase):
         self.assertTrue(is_old_seed("0123456789ABCDEF" * 4))
 
     def test_seed_type(self):
-        for seed_words, _type in self.mnemonics:
+        for idx, (seed_words, _type) in enumerate(self.mnemonics):
+            with self.subTest(msg=f"seed_type_subcase_{idx}", seed_words=seed_words):
                 self.assertEqual(_type, seed_type(seed_words), msg=seed_words)