Remove defaultdict behavior.

Fix issue with number of values for CSV data.
Document record version and effectivity dates.

aosstower/l00/parser.py

+"""
+Data Versions
+=============
+There have so far been 3 changes to the format of the raw ASCII data over the
+years.
+
+Version 0
+---------
+Effective from incept to 2010-06-01T00:27:51Z.
+
+The original data format was a key value, space separated data format
+``<key> <value>``. There were a total of 16 data values including `TIME`:
+`TIME, ACCURAIN, TEMP107_4, LI200X, TEMP107_1, RH41372, TEMP107_5, CS105,
+PAROSCI, WSPD05305, TEMP107_3, CS10162, RAIN380M, TEMP107_2, TEMP41372,
+WDIR05305`.
+
+Version 1
+---------
+Effective 2010-06-01T00:27:51Z to 2012-12-03T17:34:17Z.
+
+A CSV format file with a total of 28 values: station_id, year, doy, hhmm, sec,
+box_pressure, paro_air_temp_period, paro_pressure_period, paro_air_temp,
+pressure, paro_cal_sig, box_rh, box_air_temp, air_temp_2, air_temp_3,
+air_temp_4, wind_speed, wind_dir, rh_shield_freq, rh, air_temp_6_3m, dewpoint,
+rtd_shield_freq, air_temp, solar_flux, precip, accum_precip, altimeter.
+
+Version 2
+---------
+Effective 2012-12-03T17:34:17Z to present.
+
+Same as Version 1 with the addition of altimeter2 at the end. I'm not sure why
+we have 2 altimeter values but as far as I know altimeter2 is not used.
+"""
 
-# coding=utf-8
 import re
 import logging
 from datetime import datetime, timedelta
-from collections import defaultdict
 
 from metobs import data as d
 
@@ -45,7 +76,7 @@ def _make_record(data):
             continue
         if key in database:
             data[key] = database[key].type(data[key])
-    return defaultdict(lambda: float('nan'), data)
+    return data
 
 
 class ParserV0(object):
@@ -83,6 +114,7 @@ class ParserV0(object):
                 raw_data[self.names[k1]] = v1
             else:
                 raise LineParseError("Unexpected var: %s" % k1, line)
+        raw_data['version'] = 0
         try:
             time_str = parts[1]
             unix_time = int(time_str)
@@ -92,7 +124,7 @@ class ParserV0(object):
         return _make_record(raw_data)
 
 
-class ParserV1(object):
+class ParserV1V2(object):
 
     names = ['station_id', 'year', 'doy', 'hhmm', 'sec', 'box_pressure',
              'paro_air_temp_period', 'paro_pressure_period', 'paro_air_temp',
@@ -100,7 +132,7 @@ class ParserV1(object):
              'air_temp_2', 'air_temp_3', 'air_temp_4', 'wind_speed', 'wind_dir',
              'rh_shield_freq', 'rh', 'air_temp_6_3m', 'dewpoint',
              'rtd_shield_freq', 'air_temp', 'solar_flux', 'precip',
-             'accum_precip', 'altimeter']
+             'accum_precip', 'altimeter']  # , 'altimeter2']
 
     @staticmethod
     def maybe_mine(line):
@@ -118,9 +150,10 @@ class ParserV1(object):
 
     def parse(self, line):
         parts = line.split(',')
-        if len(parts) != 29:
-            raise LineParseError("Expected 28 parts", line)
+        if len(parts) < 28:
+            raise LineParseError("Expected >= 28 parts", line)
         raw_data = {k: v for k, v in zip(self.names, parts)}
+        raw_data['version'] = 1 if len(parts) == 28 else 2
         try:
             raw_data['stamp'] = self._get_stamp(raw_data)
         except (TypeError, ValueError):
@@ -138,12 +171,17 @@ def read_records(source, error_handler=lambda *a: None):
         fptr = open(source)
 
     for idx, line in enumerate(fptr.readlines()):
-        for parser in [ParserV1(), ParserV0()]:
+        if not line.strip() or line.startswith('#'):
+            continue
+        for parser in [ParserV1V2(), ParserV0()]:
             if parser.maybe_mine(line):
                 try:
                     yield parser.parse(line)
-                    break  # forces 'else' to execute
                 except LineParseError as err:
                     error_handler(idx + 1, line, err)
+                break
+
+        # yes, I know a for/else is obscure, but in this case it does
+        # exactly what I need, it only executes if `break` does not execute
         else:
             error_handler(idx + 1, line, RuntimeError("no parser found", line))