Minor Description
The Avro spec says
Default values for bytes and fixed fields are JSON strings, where Unicode code points 0-255 are mapped to unsigned 8-bit byte values 0-255.
but in the Avro library for Python, _read_default_value calls str.encode to convert the JSON string to bytes, and str.encode in Python 3 uses UTF-8 by default. So, this miscodes bytes 0x80 and higher. For example, the JSON string "\u0080" becomes two bytes b'\xc2\x80' even though it should become one byte b'\x80'.