obj.py: remove 'on_fail' keyword arg

- During initialization, data objects now invariably raise an exception on
  failure (ObjectInitError by default, configurable via the 'exc' attribute).

- For callers that need to handle the exception, the new get_obj() wrapper is
  provided.

Testing:

    $ test/objtest.py -S
    $ test/objtest.py -S --getobj

mmgen/addr.py

@@ -1159,7 +1159,7 @@ async def add_tw_data(self,wallet):
 		twd = await self.get_tw_data(wallet)
 		out,i = {},0
 		for acct,addr_array in twd:
-			l = TwLabel(self.proto,acct,on_fail='silent')
+			l = get_obj(TwLabel,proto=self.proto,text=acct,silent=True)
 			if l and l.mmid.type == 'mmgen':
 				obj = l.mmid.obj
 				if len(addr_array) != 1:

mmgen/altcoins/eth/tw.py

@@ -257,7 +257,7 @@ async def get_unspent_rpc(self):
 		if self.addrs:
 			wl = [d for d in wl if d['addr'] in self.addrs]
 		return [{
-				'account': TwLabel(self.proto,d['mmid']+' '+d['comment'],on_fail='raise'),
+				'account': TwLabel(self.proto,d['mmid']+' '+d['comment']),
 				'address': d['addr'],
 				'amount': await self.wallet.get_balance(d['addr']),
 				'confirmations': 0, # TODO
@@ -298,7 +298,7 @@ async def __ainit__(self,proto,usr_addr_list,minconf,showempty,showbtcaddrs,all_
 		from mmgen.obj import CoinAddr
 		for mmid,d in list(tw_dict.items()):
 #			if d['confirmations'] < minconf: continue # cannot get confirmations for eth account
-			label = TwLabel(self.proto,mmid+' '+d['comment'],on_fail='raise')
+			label = TwLabel(self.proto,mmid+' '+d['comment'])
 			if usr_addr_list and (label.mmid not in usr_addr_list):
 				continue
 			bal = await self.wallet.get_balance(d['addr'])

mmgen/exception.py

@@ -40,10 +40,11 @@ class InvalidTokenAddress(Exception):     mmcode = 2
 class UnrecognizedTokenSymbol(Exception): mmcode = 2
 class TokenNotInBlockchain(Exception):    mmcode = 2
 class TokenNotInWallet(Exception):        mmcode = 2
-class BadTwComment(Exception):            mmcode = 2
+class BadTwLabel(Exception):              mmcode = 2
 class BaseConversionError(Exception):     mmcode = 2
 class BaseConversionPadError(Exception):  mmcode = 2
 class TransactionChainMismatch(Exception):mmcode = 2
+class ObjectInitError(Exception):         mmcode = 2
 
 # 3: yellow hl, 'MMGen Error' + exception + message
 class RPCFailure(Exception):              mmcode = 3

mmgen/main_split.py

@@ -104,7 +104,7 @@
 
 from .obj import MMGenID
 try:
-	mmids = [MMGenID(a,on_fail='die') for a in cmd_args]
+	mmids = [MMGenID(a) for a in cmd_args]
 except:
 	die(1,'Command line arguments must be valid MMGen IDs')
 

mmgen/main_wallet.py

@@ -148,10 +148,10 @@
 	from .obj import SubSeedIdx
 	ss_idx = SubSeedIdx(cmd_args.pop())
 elif invoked_as == 'seedsplit':
-	from .obj import SeedSplitSpecifier
+	from .obj import get_obj,SeedSplitSpecifier
 	master_share = MasterShareIdx(opt.master_share) if opt.master_share else None
 	if cmd_args:
-		sss = SeedSplitSpecifier(cmd_args.pop(),on_fail='silent')
+		sss = get_obj(SeedSplitSpecifier,s=cmd_args.pop(),silent=True)
 		if master_share:
 			if not sss:
 				sss = SeedSplitSpecifier('1:2')