Return whether the provided file is a CSV file or not.
    This checks if the first row of the file can be splitted by ',' and
    if the resulting line contains more than 4 columns (Markers, linkage
    group, chromosome, trait).

def is_excel_file(inputfile):
    """ Return whether the provided file is a CSV file or not.
    This checks if the first row of the file can be splitted by ',' and
    if the resulting line contains more than 4 columns (Markers, linkage
    group, chromosome, trait).

    """
    try:
        xlrd.open_workbook(inputfile)
    except Exception as err:
        print(err)
        return False
    return True