def GetPopList(sample_blocks):
    """
    Get a list of populations in the sample_blocks
    ----------
    sample_blocks : list of [hap_blocks]
       each hap_block is a dictionary with keys
       'pop', 'chrom', 'start', 'end'

    Returns
    -------
    poplist : list of str
       list of populations represented in the blocks
    """
    poplist = set()
    for i in range(len(sample_blocks)):
        for sb in sample_blocks[i]:
            poplist.add(sb['pop'])
    return list(poplist)