Merge pull request #6772 from vladmandic/sha-calc-optimization

def calculate_sha256(filename):

    hash_sha256 = hashlib.sha256()

    blksize = 1024 * 1024

    with open(filename, "rb") as f:

        for chunk in iter(lambda: f.read(4096), b""):

        for chunk in iter(lambda: f.read(blksize), b""):

            hash_sha256.update(chunk)

    return hash_sha256.hexdigest()