detect available hardware wallets before listing them in wizard

gui/qt/installwizard.py

@@ -442,7 +442,17 @@ class InstallWizard(QDialog):
                 if not wallet_type:
                     return
             elif wallet_type == 'hardware':
-                hardware_wallets = map(lambda x:(x[1],x[2]), filter(lambda x:x[0]=='hardware', electrum.wallet.wallet_types))
+                hardware_wallets = []
+                for item in electrum.wallet.wallet_types:
+                    t, name, description, loader = item
+                    if t == 'hardware':
+                        try:
+                            p = loader()
+                        except:
+                            util.print_error("cannot load plugin for:", name)
+                            continue
+                        if p:
+                            hardware_wallets.append((name, description))
                 wallet_type = self.choice(_("Hardware Wallet"), 'Select your hardware wallet', hardware_wallets)
 
                 if not wallet_type:

lib/plugins.py

@@ -49,6 +49,14 @@ def is_available(name, w):
     return True
 
 
+def plugin_loader(config, name):
+    global plugins
+    if plugins.get(name) is None:
+        print_error(_("Loading plugin by constructor:"), name)
+        p = loader(name)
+        plugins[name] = p.Plugin(config, name)
+    return plugins[name]
+
 @profiler
 def init_plugins(config, is_local, gui_name):
     global plugins, descriptions, loader
@@ -60,20 +68,9 @@ def init_plugins(config, is_local, gui_name):
         electrum_plugins = __import__('electrum_plugins')
         loader = lambda name: __import__('electrum_plugins.' + name, fromlist=['electrum_plugins'])
 
-    def constructor(name, storage):
-        if plugins.get(name) is None:
-            try:
-                print_error(_("Loading plugin by constructor:"), name)
-                p = loader(name)
-                plugins[name] = p.Plugin(config, name)
-            except:
-                print_msg(_("Error: cannot initialize plugin"), name)
-                return
-        return plugins[name].constructor(storage)
-
-    def register_wallet_type(name, x, constructor):
+    def register_wallet_type(name, x):
         import wallet
-        x += (lambda storage: constructor(name, storage),)
+        x += (lambda: plugin_loader(config, name),)
         wallet.wallet_types.append(x)
 
     descriptions = electrum_plugins.descriptions
@@ -83,7 +80,7 @@ def init_plugins(config, is_local, gui_name):
             continue
         x = item.get('registers_wallet_type')
         if x:
-            register_wallet_type(name, x, constructor)
+            register_wallet_type(name, x)
         if not config.get('use_' + name):
             continue
         try:

lib/wallet.py

@@ -1925,9 +1925,9 @@ class Wallet(object):
 
         wallet_type = storage.get('wallet_type')
         if wallet_type:
-            for cat, t, name, c in wallet_types:
+            for cat, t, name, loader in wallet_types:
                 if t == wallet_type:
-                    WalletClass = c
+                    WalletClass = lambda storage: apply(loader().constructor, (storage,))
                     break
             else:
                 if re.match('(\d+)of(\d+)', wallet_type):