Create a rgb-to-hex converter
Level: Intermediate (score: 3)
Designer Mary wants to convert her CSS from statements like background-color: rgb(128, 128, 0); to: background-color: #808000;.
Don't worry, you don't have to rewrite CSS, just complete the rgb_to_hex helper for her that takes a tuple of RGB (3 ints) and converts it to the corresponding hex value.
For example for Maroon you would call it like rgb_to_hex((128, 0, 0)) and it would return the hex #800000.
Make sure you check that each r, g and b int is within the valid range of 0 and 255 (both included), if not raise a ValueError, Explicit is better than implicit (Zen).
Check the TESTS tab for more examples, there we check your code for 16 colors and 3 excepions. Have fun!