Merge pull request #1150 from Shevonar/fix-rosbag-python3

Fix rosbag API for Python 3

tools/rosbag/src/rosbag/bag.py

@@ -1586,6 +1586,7 @@ def _read_uint32(f): return _unpack_uint32(f.read(4))
 def _read_uint64(f): return _unpack_uint64(f.read(8))
 def _read_time (f): return _unpack_time (f.read(8))
 
+def _decode_str(v): return v if type(v) is str else v.decode()
 def _unpack_uint8(v): return struct.unpack('<B', v)[0]
 def _unpack_uint32(v): return struct.unpack('<L', v)[0]
 def _unpack_uint64(v): return struct.unpack('<Q', v)[0]
@@ -1634,8 +1635,7 @@ def _read_field(header, field, unpack_fn):
 
  return value
 
-def _read_str_field (header, field):
- return _read_field(header, field, lambda v: v)
+def _read_str_field (header, field): return _read_field(header, field, _decode_str)
 def _read_uint8_field (header, field): return _read_field(header, field, _unpack_uint8)
 def _read_uint32_field(header, field): return _read_field(header, field, _unpack_uint32)
 def _read_uint64_field(header, field): return _read_field(header, field, _unpack_uint64)