Nano Banana APIの料金とモデル比較：5モデルの選び方

OpenAI-compatible:  POST https://api.laozhang.ai/v1/chat/completions
Gemini-native:      POST https://api.laozhang.ai/v1beta/models/{model}:generateContent

"""LaoZhang APIのNano Bananaモデルで使う共通ヘルパー。"""
import base64
import json
import os
import re
import sys
from pathlib import Path

import requests
from openai import OpenAI

BASE_URL = "https://api.laozhang.ai"
INPUT_TYPES = {".png": "image/png", ".jpg": "image/jpeg", ".jpeg": "image/jpeg", ".webp": "image/webp"}
DATA_URL = re.compile(r"data:image/[\w.+-]+;base64,([A-Za-z0-9+/=]+)")


def openai_client():
    """OpenAI互換のクライアント。SDKがキーを Authorization: Bearer で送る。"""
    # max_retries=0：タイムアウト後の自動リトライで画像が二重に生成・課金されるのを防ぐ
    return OpenAI(api_key=os.environ["LAOZHANG_API_KEY"], base_url=f"{BASE_URL}/v1", timeout=300, max_retries=0)


def generate_content(model, parts, image_config=None):
    """Geminiネイティブの generateContent リクエストを送り、JSONレスポンスを返す。"""
    generation_config = {"responseModalities": ["IMAGE"]}
    if image_config:
        generation_config["imageConfig"] = image_config
    response = requests.post(
        f"{BASE_URL}/v1beta/models/{model}:generateContent",
        headers={"Authorization": f"Bearer {os.environ['LAOZHANG_API_KEY']}"},
        json={"contents": [{"role": "user", "parts": parts}], "generationConfig": generation_config},
        timeout=300,
    )
    if response.status_code != 200:
        raise RuntimeError(f"HTTP {response.status_code}: {response.text[:500]}")
    return response.json()


def _extension(raw):
    if raw.startswith(b"\x89PNG"):
        return "png"
    if raw.startswith(b"\xff\xd8\xff"):
        return "jpg"
    if raw[:4] == b"RIFF" and raw[8:12] == b"WEBP":
        return "webp"
    return "bin"


def _write(encoded, stem, number):
    encoded = "".join(encoded.split())
    raw = base64.b64decode(encoded + "=" * (-len(encoded) % 4))  # 不足している = を補う
    suffix = "" if number == 1 else f"-{number}"
    path = Path(f"{stem}{suffix}.{_extension(raw)}")
    path.write_bytes(raw)
    return str(path)


def save_chat_images(content, stem):
    """OpenAI互換：message.content に含まれるBase64のデータURLをすべて保存する。"""
    found = DATA_URL.findall(content or "")
    if not found:
        raise RuntimeError(f"message.content に画像がありません: {(content or '')[:300]!r}")
    return [_write(data, stem, number) for number, data in enumerate(found, start=1)]


def save_native_images(result, stem):
    """Geminiネイティブ：candidates[].content.parts[] 内の inlineData 画像をすべて保存する。"""
    blobs = []
    for candidate in result.get("candidates") or []:
        for part in (candidate.get("content") or {}).get("parts") or []:
            blob = part.get("inlineData") or part.get("inline_data")
            if blob and not part.get("thought"):
                blobs.append(blob)
    if not blobs:
        reasons = [candidate.get("finishReason") for candidate in result.get("candidates") or []]
        raise RuntimeError(f"画像が返されませんでした: {result.get('promptFeedback') or reasons}")
    return [_write(blob["data"], stem, number) for number, blob in enumerate(blobs, start=1)]


def _encode(path):
    mime = INPUT_TYPES.get(Path(path).suffix.lower())
    if mime is None:
        raise ValueError(f"PNG、JPEG、WebPのいずれかのファイルを指定してください: {path}")
    return mime, base64.b64encode(Path(path).read_bytes()).decode("ascii")


def to_data_url(path):
    """ローカルファイルを、OpenAI互換の image_url パート用データURLに変換する。"""
    mime, data = _encode(path)
    return f"data:{mime};base64,{data}"


def to_inline_part(path):
    """ローカルファイルを、Geminiネイティブの inlineData パートに変換する。"""
    mime, data = _encode(path)
    return {"inlineData": {"mimeType": mime, "data": data}}


if __name__ == "__main__":
    # レスポンスファイルの画像を保存する：python nano_banana.py response.json output-name
    body = json.loads(Path(sys.argv[1]).read_text(encoding="utf-8"))
    if "error" in body:
        sys.exit(f"APIエラー: {body['error']}")
    if "choices" in body:
        saved = save_chat_images(body["choices"][0]["message"].get("content"), sys.argv[2])
    else:
        saved = save_native_images(body, sys.argv[2])
    for path in saved:
        print("保存しました", path)

from nano_banana import generate_content, save_native_images

result = generate_content(
    "gemini-2.5-flash-image",
    [{"text": "Generate an image of a lighthouse on a rocky coast at dusk, wide cinematic view."}],
    image_config={"aspectRatio": "16:9"},
)
for path in save_native_images(result, "standard-lighthouse"):
    print("保存しました", path)

from nano_banana import openai_client, save_chat_images, to_data_url

response = openai_client().chat.completions.create(
    model="gemini-2.5-flash-image",
    messages=[{
        "role": "user",
        "content": [
            {"type": "text", "text": "Replace the background with a plain light-gray studio wall. Keep the product unchanged."},
            {"type": "image_url", "image_url": {"url": to_data_url("product.jpg")}},
        ],
    }],
)
for path in save_chat_images(response.choices[0].message.content, "standard-edit"):
    print("保存しました", path)

from nano_banana import generate_content, save_native_images

result = generate_content(
    "gemini-3.1-flash-image",
    [{"text": "Generate an image of a lighthouse on a rocky coast at dusk, wide cinematic view."}],
    image_config={"aspectRatio": "16:9", "imageSize": "2K"},
)
for path in save_native_images(result, "lighthouse-2k"):
    print("保存しました", path)

{
  "contents": [{
    "role": "user",
    "parts": [
      {"text": "Dress the person in the first image in the jacket from the second image."},
      {"fileData": {"mimeType": "image/jpeg", "fileUri": "https://cdn.example.com/person.jpg"}},
      {"inlineData": {"mimeType": "image/png", "data": "<Base64 data of the jacket image>"}}
    ]
  }],
  "generationConfig": {"responseModalities": ["IMAGE"]}
}