trezor-firmware/src/apps/common/hash_writer.py

class HashWriter:

    def __init__(self, hashfunc):
        self.ctx = hashfunc()
        self.buf = bytearray(1)  # used in append()

    def extend(self, buf: bytearray):
        self.ctx.update(buf)

    def append(self, b: int):
        self.buf[0] = b
        self.ctx.update(self.buf)

    def get_digest(self, *args) -> bytes:
        return self.ctx.digest(*args)