#!/usr/bin/env python3

import hashlib

import sys


def fail(msg=""):
    sys.stderr.write("Error: %s\n" % msg)
    sys.exit(1)


def get_sha256(filename, block_size=65536):
    sha256 = hashlib.sha256()
    with open(filename, 'rb') as f:
        for block in iter(lambda: f.read(block_size), b''):
            sha256.update(block)
    return sha256.hexdigest()