RF: Move dicom import into test function

Include a comment about why the tag might be missing.

Author: moloney

nibabel/nicom/csareader.py

@@ -66,6 +66,7 @@ def get_csa_header(dcm_data, csa_type='image'):
     try:
         tag = dcm_data[(0x29, element_no)]
     except KeyError:
+        # The element could be missing due to anonymization
         return None
     return read(tag.value)
 

nibabel/nicom/tests/test_csareader.py

@@ -14,8 +14,6 @@
 
 from .test_dicomwrappers import (have_dicom, dicom_test,
                                  IO_DATA_PATH, DATA, DATA_FILE)
-if have_dicom:
-    from .test_dicomwrappers import pydicom
 
 CSA2_B0 = open(pjoin(IO_DATA_PATH, 'csa2_b0.bin'), 'rb').read()
 CSA2_B1000 = open(pjoin(IO_DATA_PATH, 'csa2_b1000.bin'), 'rb').read()
@@ -138,8 +136,12 @@ def test_missing_csa_elem():
     # Test that we get None instead of raising an Exception when the file has
     # the PrivateCreator element for the CSA dict but not the element with the
     # actual CSA header (perhaps due to anonymization)
+    try:
+        from dicom.tag import Tag
+    except ImportError:
+        from pydicom.tag import Tag
     dcm = deepcopy(DATA)
-    csa_tag = pydicom.tag.Tag(0x29, 0x1010)
+    csa_tag = Tag(0x29, 0x1010)
     del dcm[csa_tag]
     hdr = csa.get_csa_header(dcm, 'image')
     assert_equal(hdr, None)