Addressed's @jchoude's comments

Author: MarcCote

nibabel/streamlines/tck.py

@@ -15,7 +15,8 @@
 
 from .array_sequence import ArraySequence
 from .tractogram_file import TractogramFile
-from .tractogram_file import HeaderError, DataWarning, DataError
+from .tractogram_file import HeaderWarning, DataWarning
+from .tractogram_file import HeaderError, DataError
 from .tractogram import TractogramItem, Tractogram, LazyTractogram
 from .header import Field
 
@@ -306,21 +307,29 @@ def _read_header(fileobj):
             while not buf.rstrip().endswith("END"):
                 buf += asstr(f.fobj.readline())
 
+            offset_data = f.tell()
+
         # Build header dictionary from the buffer.
         hdr = dict(item.split(': ') for item in buf.rstrip().split('\n')[:-1])
         hdr[Field.MAGIC_NUMBER] = magic_number
 
         # Check integrity of TCK header.
         if 'datatype' not in hdr:
-            raise HeaderError("Missing 'datatype' attribute in TCK header.")
+            msg = ("Missing 'datatype' attribute in TCK header."
+                   " Assuming it is Float32LE.")
+            warnings.warn(msg, HeaderWarning)
+            hdr['datatype'] = "Float32LE"
 
         if not hdr['datatype'].startswith('Float32'):
-            msg = ("TCK only supports float32 dtype but 'dataype: {}' was"
+            msg = ("TCK only supports float32 dtype but 'datatype: {}' was"
                    " specified in the header.").format(hdr['datatype'])
             raise HeaderError(msg)
 
         if 'file' not in hdr:
-            raise HeaderError("Missing 'file' attribute in TCK header.")
+            msg = ("Missing 'file' attribute in TCK header."
+                   " Will try to guess it.")
+            warnings.warn(msg, HeaderWarning)
+            hdr['file'] = '. {}'.format(offset_data)
 
         if hdr['file'].split()[0] != '.':
             msg = ("TCK only supports single-file - in other words the"

nibabel/streamlines/tests/test_tck.py

@@ -3,18 +3,19 @@
 import numpy as np
 from os.path import join as pjoin
 
-from nibabel.externals.six import BytesIO
+from six import BytesIO
 from nibabel.py3k import asbytes
 
 from ..array_sequence import ArraySequence
 from ..tractogram import Tractogram
-from ..tractogram_file import DataError
+from ..tractogram_file import HeaderWarning, DataError
 
+from .. import tck as tck_module
 from ..tck import TckFile
 
 from nose.tools import assert_equal, assert_raises, assert_true
 from numpy.testing import assert_array_equal
-from nibabel.testing import data_path
+from nibabel.testing import data_path, clear_and_catch_warnings
 from .test_tractogram import assert_tractogram_equal
 
 DATA = {}
@@ -88,6 +89,27 @@ def test_load_file_with_wrong_information(self):
                                         asbytes("Float32BE"))
         assert_raises(DataError, TckFile.load, BytesIO(new_tck_file))
 
+        # Simulate a TCK file with no `datatype` field.
+        new_tck_file = tck_file.replace(b"datatype: Float32LE\n", b"")
+        # Adjust data offset
+        new_tck_file = new_tck_file.replace(b"\nfile: . 67\n", b"\nfile: . 47\n")
+        with clear_and_catch_warnings(record=True, modules=[tck_module]) as w:
+            tck = TckFile.load(BytesIO(new_tck_file))
+            assert_equal(len(w), 1)
+            assert_true(issubclass(w[0].category, HeaderWarning))
+            assert_true("Missing 'datatype'" in str(w[0].message))
+            assert_array_equal(tck.header['datatype'], "Float32LE")
+
+        # Simulate a TCK file with no `file` field.
+        # Adjust data offset
+        new_tck_file = tck_file.replace(b"\nfile: . 67", b"")
+        with clear_and_catch_warnings(record=True, modules=[tck_module]) as w:
+            tck = TckFile.load(BytesIO(new_tck_file))
+            assert_equal(len(w), 1)
+            assert_true(issubclass(w[0].category, HeaderWarning))
+            assert_true("Missing 'file'" in str(w[0].message))
+            assert_array_equal(tck.header['file'], ". 56")
+
     def test_write_empty_file(self):
         tractogram = Tractogram(affine_to_rasmm=np.eye(4))
 
@@ -125,15 +147,6 @@ def test_write_simple_file(self):
         assert_equal(tck_file.read(),
                      open(DATA['simple_tck_fname'], 'rb').read())
 
-        # # Add custom header fields.
-        # tck_file = BytesIO()
-        # tck = TckFile(tractogram)
-        # # tck.header['Custom_field'] = "Some_value"
-        # tck.save(tck_file)
-        # tck_file.seek(0, os.SEEK_SET)
-        # new_tck = TckFile.load(tck_file)
-        # assert_equal(tck.header, new_tck.header)
-
     def test_load_write_file(self):
         for fname in [DATA['empty_tck_fname'],
                       DATA['simple_tck_fname']]: