prize18-2  Exercise 1: Encode One Character by Hand
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Steps for U+20AC (euro sign). It is in U+0800-U+FFFF, so it uses the 3-byte pattern 1110xxxx 10xxxxxx 10xxxxxx (16 free bits).
  1. 16-bit binary of 0x20AC:        0010 000010 101100
  2. Split 4 + 6 + 6 bits:           0010 | 000010 | 101100
  3. Add the pattern bits:           11100010 | 10000010 | 10101100
  4. In hex:                         E2 82 AC

ex1.py:

  cp = 0x20AC
  print(f"{cp:016b}")
  b1 = 0b11100000 | (cp >> 12)
  b2 = 0b10000000 | ((cp >> 6) & 0b111111)
  b3 = 0b10000000 | (cp & 0b111111)
  mine = bytes([b1, b2, b3])
  print(" ".join(f"{b:08b}" for b in mine), mine.hex(" "))
  print(mine == "\u20ac".encode("utf-8"))

Real output (Python 3.14):

  0010000010101100
  11100010 10000010 10101100 e2 82 ac
  True

Note how the first byte starts with three 1s (a 3-byte character) and each later byte starts with 10 (continuation).