Store toc mask rather than dict in segments

nptdms/base_segment.py

@@ -3,6 +3,7 @@
 import numpy as np
 
 from nptdms import types
+from nptdms.common import toc_properties
 from nptdms.log import log_manager
 
 
@@ -14,16 +15,16 @@ class BaseSegment(object):
     """
 
     __slots__ = [
-        'position', 'num_chunks', 'ordered_objects', 'toc',
+        'position', 'num_chunks', 'ordered_objects', 'toc_mask',
         'next_segment_offset', 'next_segment_pos',
         'raw_data_offset', 'data_position', 'final_chunk_proportion',
         'endianness']
 
     def __init__(
-            self, position, toc, endianness, next_segment_offset,
+            self, position, toc_mask, endianness, next_segment_offset,
             next_segment_pos, raw_data_offset, data_position):
         self.position = position
-        self.toc = toc
+        self.toc_mask = toc_mask
         self.endianness = endianness
         self.next_segment_offset = next_segment_offset
         self.next_segment_pos = next_segment_pos
@@ -45,7 +46,7 @@ def read_segment_objects(self, file, previous_segment_objects, previous_segment=
         :param previous_segment: Previous segment in the file.
         """
 
-        if not self.toc["kTocMetaData"]:
+        if not self.toc_mask & toc_properties['kTocMetaData']:
             try:
                 self.ordered_objects = previous_segment.ordered_objects
                 self._calculate_chunks()
@@ -55,7 +56,7 @@ def read_segment_objects(self, file, previous_segment_objects, previous_segment=
                     "kTocMetaData is not set for segment but "
                     "there is no previous segment")
 
-        if not self.toc["kTocNewObjList"]:
+        if not self.toc_mask & toc_properties['kTocNewObjList']:
             # In this case, there can be a list of new objects that
             # are appended, or previous objects can also be repeated
             # if their properties change
@@ -75,7 +76,7 @@ def read_segment_objects(self, file, previous_segment_objects, previous_segment=
             # re-using any properties from previous segments.
             updating_existing = False
             segment_obj = None
-            if not self.toc["kTocNewObjList"]:
+            if not self.toc_mask & toc_properties['kTocNewObjList']:
                 # Search for the same object from the previous segment
                 # object list.
                 for obj in self.ordered_objects:
@@ -108,7 +109,7 @@ def read_raw_data(self, f):
             objects in this segment.
         """
 
-        if not self.toc["kTocRawData"]:
+        if not self.toc_mask & toc_properties['kTocRawData']:
             yield DataChunk.empty()
 
         f.seek(self.data_position)

nptdms/tdms_segment.py

@@ -1,3 +1,4 @@
+import logging
 import os
 import numpy as np
 
@@ -7,22 +8,21 @@
     BaseSegment, BaseSegmentObject, DataChunk, read_interleaved_segment_bytes, fromfile)
 from nptdms.daqmx import DaqmxSegment
 from nptdms.log import log_manager
-from nptdms.utils import OrderedDict
 
 
 log = log_manager.get_logger(__name__)
 
 
 def read_segment_metadata(file, previous_segment_objects, previous_segment=None):
-    (position, toc, endianness, data_position, raw_data_offset,
+    (position, toc_mask, endianness, data_position, raw_data_offset,
      next_segment_offset, next_segment_pos) = read_lead_in(file)
 
     segment_args = (
-        position, toc, endianness, next_segment_offset,
+        position, toc_mask, endianness, next_segment_offset,
         next_segment_pos, raw_data_offset, data_position)
-    if toc['kTocDAQmxRawData']:
+    if toc_mask & toc_properties['kTocDAQmxRawData']:
         segment = DaqmxSegment(*segment_args)
-    elif toc["kTocInterleavedData"]:
+    elif toc_mask & toc_properties['kTocInterleavedData']:
         segment = InterleavedDataSegment(*segment_args)
     else:
         segment = ContiguousDataSegment(*segment_args)
@@ -50,13 +50,12 @@ def read_lead_in(file):
     # Next four bytes are table of contents mask
     toc_mask = types.Int32.read(file)
 
-    toc = OrderedDict()
-    for prop_name, prop_mask in toc_properties.items():
-        prop_is_set = (toc_mask & prop_mask) != 0
-        toc[prop_name] = prop_is_set
-        log.debug("Property %s is %s", prop_name, prop_is_set)
+    if log.isEnabledFor(logging.DEBUG):
+        for prop_name, prop_mask in toc_properties.items():
+            prop_is_set = (toc_mask & prop_mask) != 0
+            log.debug("Property %s is %s", prop_name, prop_is_set)
 
-    endianness = '>' if toc['kTocBigEndian'] else '<'
+    endianness = '>' if (toc_mask & toc_properties['kTocBigEndian']) else '<'
 
     # Next four bytes are version number
     version = types.Int32.read(file, endianness)
@@ -91,7 +90,7 @@ def read_lead_in(file):
         next_segment_pos = (
                 position + next_segment_offset + lead_size)
 
-    return (position, toc, endianness, data_position, raw_data_offset,
+    return (position, toc_mask, endianness, data_position, raw_data_offset,
             next_segment_offset, next_segment_pos)
 
 

nptdms/writer.py

@@ -1,6 +1,5 @@
 """Module for writing TDMS files"""
 
-from collections import namedtuple
 try:
     from collections import OrderedDict
 except ImportError:
@@ -95,7 +94,7 @@ def write(self, file):
         metadata = self.metadata()
         metadata_size = sum(len(val.bytes) for val in metadata)
 
-        toc = ["kTocMetaData", "kTocRawData", "kTocNewObjList"]
+        toc = ['kTocMetaData', 'kTocRawData', 'kTocNewObjList']
         leadin = self.leadin(toc, metadata_size)
 
         file.write(b''.join(val.bytes for val in leadin))
@@ -138,9 +137,8 @@ def leadin(self, toc, metadata_size):
         leadin.append(Bytes(b'TDSm'))
 
         toc_mask = long(0)
-        for toc_key, toc_val in toc_properties.items():
-            if toc_key in toc:
-                toc_mask = toc_mask | toc_val
+        for toc_flag in toc:
+            toc_mask = toc_mask | toc_properties[toc_flag]
         leadin.append(Int32(toc_mask))
 
         tdms_version = 4712