genwallet.py: Minor improvments

Changes from top to bottom:
- Add header comment
- Import wallet_utils (needed for DEFAULT_MIXDEPTH)
- Make password optional in usage string
- Set variable wallet_name at the top where options are parsed
- Use DEFAULT_MIXDEPTH instead of hardcoded value

scripts/genwallet.py

@@ -1,33 +1,41 @@
 #!/usr/bin/env python3
 
+# A script for noninteractively creating wallets.
+# The implementation is similar to wallet_generate_recover_bip39 in jmclient/wallet_utils.py
+
 import sys
 import os
 from optparse import OptionParser
-from jmclient import load_program_config, add_base_options, SegwitWallet, SegwitLegacyWallet, create_wallet, jm_single
+from jmclient import (
+    load_program_config, add_base_options, SegwitWallet, SegwitLegacyWallet,
+    create_wallet, jm_single, wallet_utils
+)
 from jmbase.support import get_log, jmprint
 
 log = get_log()
 
 def main():
     parser = OptionParser(
-    usage='usage: %prog [options] wallet_file_name password',
-    description='Create a wallet with the given wallet name and password.')
+        usage='usage: %prog [options] wallet_file_name [password]',
+        description='Create a wallet with the given wallet name and password.'
+    )
     add_base_options(parser)
     (options, args) = parser.parse_args()
+    wallet_name = args[0]
     if options.wallet_password_stdin:
-        stdin = sys.stdin.read()
-        password = stdin.encode("utf-8")
+        password = sys.stdin.read().encode("utf-8")
     else:
         assert len(args) > 1, "must provide password via stdin (see --help), or as second argument."
         password = args[1].encode("utf-8")
+
     load_program_config(config_path=options.datadir)
     wallet_root_path = os.path.join(jm_single().datadir, "wallets")
-    wallet_name = os.path.join(wallet_root_path, args[0])
+    wallet_path = os.path.join(wallet_root_path, wallet_name)
     if jm_single().config.get("POLICY", "native") == "true":
         walletclass = SegwitWallet
     else:
         walletclass = SegwitLegacyWallet
-    wallet = create_wallet(wallet_name, password, 4, walletclass)
+    wallet = create_wallet(wallet_path, password, wallet_utils.DEFAULT_MIXDEPTH, walletclass)
     jmprint("recovery_seed:{}"
          .format(wallet.get_mnemonic_words()[0]), "important")
     wallet.close()