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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _known_populations(row, pops):
 """Find variants present in substantial frequency in population databases. """

    cutoff = 0.01
    out = set([])
    for pop, base in [("esp", "af_esp_all"), ("1000g", "af_1kg_all"),
                      ("exac", "af_exac_all"), ("anypop", "max_aaf_all")]:
        for key in [x for x in pops if x.startswith(base)]:
            val = row[key]
            if val and val > cutoff:
                out.add(pop)
    return sorted(list(out))