def hex2binstr(bstr):
    t = {
        "0" : '0000',
        "1" : '0001',
        "2" : '0010',
        "3" : '0011',
        "4" : '0100',
        "5" : '0101',
        "6" : '0110',
        "7" : '0111',
        "8" : '1000',
        "9" : '1001',
        "a" : '1010',
        "b" : '1011',
        "c" : '1100',
        "d" : '1101',
        "e" : '1110',
        "f" : '1111',
    }

    o = ""
    for b in bstr:
        o = o + t[b]
    return o

print(hex2binstr("d4f3"))
print(hex2binstr("caf3"))