def save(nifti_filename, numpy_data):
<EOL>nifti_filename = os.path.expanduser(nifti_filename)<EOL>try:<EOL><INDENT>nifti_img = nib.Nifti1Image(numpy_data, numpy.eye(<NUM_LIT:4>))<EOL>nib.save(nifti_img, nifti_filename)<EOL><DEDENT>except Exception as e:<EOL><INDENT>raise ValueError("<STR_LIT>".format(nifti_filename))<EOL><DEDENT>return nifti_filename<EOL>
Export a numpy array to a nifti file.  TODO: currently using dummy
headers and identity matrix affine transform. This can be expanded.

Arguments:
    nifti_filename (str): A filename to which to save the nifti data
    numpy_data (numpy.ndarray): The numpy array to save to nifti

Returns:
    String. The expanded filename that now holds the nifti data