def commas(x):

    x = round(x, 3)
    if x == round(x):
        x = int(x)

    sgn = x < 0
    if sgn:
        x = -x
    s = str(x)
    a = s.split('.')
    s = a[0]
    s = ''.join(reversed(list(s)))
    res = ''
    for i in range(len(s)):
        res += s[i]
        if i % 3 == 2 and i != len(s) - 1:
            res += ','
    res = ''.join(reversed(list(res)))
    if len(a) == 2:
        res += '.' + a[1]

    if sgn:
        res = '-' + res
    return res


assert commas(1) == "1"
assert commas(1000) == "1,000"
assert commas(100.2346) == "100.235"
assert commas(1000000000.23) == "1,000,000,000.23"
assert commas(-999.9999) == "-1,000"
assert commas(-1234567.0001236) == "-1,234,567"
print("TEST PASSED")