break db load into smaller functions, load backup if opening primary db fails

bin/autojump

@@ -104,19 +104,44 @@ class Database:
         Try to open the database file, recovering from backup if needed.
         """
         if os.path.exists(self.filename):
+            try:
                 with open(self.filename, 'r') as f:
                     for line in f.readlines():
                         weight, path = line[:-1].split("\t", 1)
                         path = decode(path, 'utf-8')
                         self.data[path] = float(weight)
-        elif os.path.exists(self.filename + '.bak'):
+            except (IOError, EOFError):
+                self.load_backup(error_recovery)
+        else:
+            self.load_backup(error_recovery)
+
+    def load_backup(self, error_recovery = False):
+        """
+        Loads database from backup file.
+        """
+        if os.path.exists(self.filename + '.bak'):
             if not error_recovery:
                 print('Problem with autojump database,\
                         trying to recover from backup...', file=sys.stderr)
                 shutil.copy(self.filename + '.bak', self.filename)
                 return self.load(True)
             else:
-                # migration code, autojump_py last used in v17
+                self.migrate()
+
+    def maintenance(self):
+        """
+        Trims and decays database entries when exceeding settings.
+        """
+        if sum(self.data.values()) > MAX_KEYWEIGHT:
+            self.decay()
+        if len(self.data) > MAX_STORED_PATHS:
+            self.trim()
+        self.save()
+
+    def migrate(self):
+        """
+        Migrates database from old format autojump_py, last used in release-v17.
+        """
         self.filename = get_db_file('autojump_py')
         if os.path.exists(self.filename):
             try: # fix to get optimised pickle in python < 3
@@ -140,16 +165,6 @@ class Database:
                 pass
         return {} # if everything fails, return an empty dictionary
 
-    def maintenance(self):
-        """
-        Trims and decays database entries when exceeding settings.
-        """
-        if sum(self.data.values()) > MAX_KEYWEIGHT:
-            self.decay()
-        if len(self.data) > MAX_STORED_PATHS:
-            self.trim()
-        self.save()
-
     def purge(self):
         """
         Deletes all entries that no longer exist on system.

tests/runtests.py

@@ -91,7 +91,7 @@ class TestAutojump(unittest.TestCase):
             os.remove(fname)
             os.remove(fname + '.bak')
 
-    def test_db_load_migrate(self):
+    def test_db_migration(self):
         ORIG_CONFIG_DIR = autojump.CONFIG_DIR
         try:
             # setup
@@ -101,8 +101,8 @@ class TestAutojump(unittest.TestCase):
             fname = CONFIG_DIR + '/autojump_py'
             db = autojump.Database(fname)
             db.add('/1')
-            shutil.copy(fname, fname + '.bak')
             db.add('/2')
+            shutil.copy(fname, fname + '.bak')
 
             # test
             missing_fname = '/tmp/autojump_test_db_load_missing_' + str(random.randint(0,32678)) + '.txt'