On demand duplicate check during runtime with a 'growing' BKTree

[sla-te]

What I would like to achieve I about the following:

EXISTING_HASHES: set = set()
def is_duplicate(img_bytes: bytes):
    if get_hash(img_bytes) in EXISTING_HASHES:
        return True
    return False

def main():
    image_bytes = get_new_image()
    if is_duplicate(image_bytes)
        return

    with open(file) as f:
       f.write(image_bytes)