Nexrad fixes

metpy/io/nexrad.py

@@ -19,6 +19,7 @@
 exporter = Exporter(globals())
 
 log = logging.getLogger("metpy.io.nexrad")
+log.addHandler(logging.StreamHandler())  # Python 2.7 needs a handler set
 log.setLevel(logging.WARNING)
 
 
@@ -241,6 +242,11 @@ def _read_data(self):
                 self._buffer.jump_to(msg_start,
                                      self.CTM_HEADER_SIZE + 2 * msg_hdr.size_hw)
 
+        # Check if we have any message segments still in the buffer
+        if self._msg_buf:
+            log.warning('Remaining buffered messages segments for message type(s): %s',
+                        ' '.join(map(str, self._msg_buf.keys())))
+
         del self._msg_buf
 
     msg1_fmt = NamedStruct([('time_ms', 'L'), ('date', 'H'),
@@ -588,10 +594,19 @@ def _decode_msg31(self, msg_hdr):
 
     def _buffer_segment(self, msg_hdr):
         # Add to the buffer
-        bufs = self._msg_buf.setdefault(msg_hdr.msg_type, bytearray())
-        bufs.extend(self._buffer.read(2 * msg_hdr.size_hw - self.msg_hdr_fmt.size))
-        if msg_hdr.segment_num == msg_hdr.num_segments:
-            return bufs
+        bufs = self._msg_buf.setdefault(msg_hdr.msg_type, dict())
+        bufs[msg_hdr.segment_num] = self._buffer.read(2 * msg_hdr.size_hw -
+                                                      self.msg_hdr_fmt.size)
+
+        # Warn for badly formatted data
+        if len(bufs) != msg_hdr.segment_num:
+            log.warning('Segment out of order (Got: %d Count: %d) for message type %d.',
+                        msg_hdr.segment_num, len(bufs), msg_hdr.msg_type)
+
+        # If we're complete, return the full collection of data
+        if msg_hdr.num_segments == len(bufs):
+            self._msg_buf.pop(msg_hdr.msg_type)
+            return b''.join(bytes(item[1]) for item in sorted(bufs.items()))
 
     def _add_sweep(self, hdr):
         if not self.sweeps and not hdr.rad_status & START_VOLUME:

metpy/io/tests/test_nexrad.py

@@ -1,4 +1,5 @@
 import glob
+import logging
 import os.path
 
 import numpy as np
@@ -9,6 +10,9 @@
 
 get_test_data = nose.tools.nottest(get_test_data)
 
+# Turn off the warnings for tests
+logging.getLogger("metpy.io.nexrad").setLevel(logging.CRITICAL)
+
 
 def test_level3_generator():
     datadir = get_test_data('nids', as_file_obj=False)
@@ -21,8 +25,9 @@ def read_level3_file(fname):
 
 # 1999 file tests old message 1
 # KFTG tests bzip compression and newer format for a part of message 31
+# KTLX 2015 has missing segments for message 18, which was causing exception
 level2_files = ['KTLX20130520_201643_V06.gz', 'KTLX19990503_235621.gz',
-                'Level2_KFTG_20150430_1419.ar2v']
+                'Level2_KFTG_20150430_1419.ar2v', 'KTLX20150530_000802_V06.bz2']
 
 
 def test_level2_generator():

metpy/io/tools.py

@@ -103,7 +103,8 @@ def __call__(self, val):
             if not val:
                 break
 
-        return l if len(l) > 1 else l[0]
+        # Return whole list if empty or multiple items, otherwise just single item
+        return l[0] if len(l) == 1 else l
 
 
 class Array(object):