*python* no loops please

Write a program that takes the size of a file (in bytes) as input from the user and converts it to the nearest whole number binary prefix (B for byte, KB for kilobyte, MB for megabyte, GB for gigabyte), rounded down. Any file sizes greater than 1024 GB should just be converted to GB. Remember that there are 2^10 bytes in a kilobyte (not 1000), 2^20 bytes in a megabyte, and 2^30 bytes in a gigabyte.