import hashlib


def get_hash(filename):
    """Calculate SHA256 checksum for file"""
    buffer_size = 65536
    sha256 = hashlib.sha256()
    with open(filename, "rb") as file:
        while True:
            chunk = file.read(buffer_size)
            if not chunk:
                break
            sha256.update(chunk)
    return sha256.hexdigest()