Make parser state logic a bit more bearable

gcconv.py

 # coding=utf-8
 """Convert Bank statement CSV to Gnucash-acceptable format"""
 
+from collections import namedtuple
+
+ParserState = namedtuple('ParserState', 'ths nxt')
+
 
 def valid_formats():
     return _parsers.keys()
 
     def __init__(self):
         self.transactions = []
-        self.state = False
-        self.next_state = False
+        self.state = ParserState(ths=False, nxt=False)
 
     def is_open(self):
-        return self.state
+        return self.state.ths
 
     def is_closed(self):
-        return not self.state
+        return not self.state.ths
 
     def parse_file(self, fpath, encoding='utf-8'):
         lines_read = 0
             for line in f.readlines():
                 line = line.decode(encoding).strip()
                 lines_read += 1
-                self.state = self.pick_state(line, lineno=lines_read)
+                self.state = self.advance(line, lineno=lines_read)
                 if self.is_open():
                     self.transactions.append(self.parse_line(line).to_gc())
 
     def parse_line(self, line):
         return MbankTransaction(line)
 
-    def pick_state(self, line, lineno=None):
+    def advance(self, line, lineno=None):
         """Choose parser state according to current line and line no."""
-        if self.next_state:
-            self.next_state = False
-            return True
+        if self.state.nxt:
+            return ParserState(ths=True, nxt=False)
         if self.is_closed() and line.startswith(u'#Datum uskute'):
-            self.next_state = True
-            return False
+            return ParserState(ths=False, nxt=True)
         if self.is_open() and not line:
-            return False
+            return ParserState(ths=False, nxt=False)
         return self.state
 
 
     def parse_line(self, line):
         return FioTransaction(line)
 
-    def pick_state(self, line, lineno=None):
+    def advance(self, line, lineno=None):
         """Choose parser state according to current line and line no."""
-        if self.next_state:
-            self.next_state = False
-            return True
-        if self.is_closed() and line.startswith(u'"ID operace";"Datum";'):
-            self.next_state = True
-            return False
+        if self.state.nxt:
+            return ParserState(ths=True, nxt=False)
+        if self.is_open() and line.startswith(u'"ID operace";"Datum";'):
+            return ParserState(ths=False, nxt=True)
         return self.state