##チュートリアル

####【メッセージを受信する場合】
WebhookHandlerを下記の様に設定
@handler.add(MessageEvent, message=TextMessage)

lineapi.py

from flask import Flask, request, abort

from linebot import (
    LineBotApi, WebhookHandler
)
from linebot.exceptions import (
    InvalidSignatureError
)
from linebot.models import (
    MessageEvent, TextMessage, TextSendMessage,
)

app = Flask(__name__)

line_bot_api = LineBotApi('YOUR_CHANNEL_ACCESS_TOKEN')
handler = WebhookHandler('YOUR_CHANNEL_SECRET')


@app.route("/callback", methods=['POST'])
def callback():
    # get X-Line-Signature header value
    signature = request.headers['X-Line-Signature']

    # get request body as text
    body = request.get_data(as_text=True)
    app.logger.info("Request body: " + body)

    # handle webhook body
    try:
        handler.handle(body, signature)
    except InvalidSignatureError:
        print("Invalid signature. Please check your channel access token/channel secret.")
        abort(400)

    return 'OK'


@handler.add(MessageEvent, message=TextMessage)
def handle_message(event):
    line_bot_api.reply_message(
        event.reply_token,
        TextSendMessage(text=event.message.text))


if __name__ == "__main__":
    app.run()

LINE Messaging API SDK for PythonのSynopsis/Usageから引用

####【メッセージをリプライ】
reply message API（ line_bot_api.reply_message）を呼ぶ
引数を、下記にすることで、オウム返しされる
・event.reply_token
・TextSendMessage(event.message.text)

####＜event＞
handle_messageメソッドの引数(event)

event

{
  "message": {
    "id": "10951288714213",
    "text": "Hello",
    "type": "text"
  },
  "replyToken": "73fb2d4ab910457443a96c3483f478dc",
  "source": {
    "type": "user",
    "userId": "U0d47ada1d7ca738641228d4599c9d347"
  },
  "timestamp": 1574264703712,
  "type": "message"
}

##引用
LINE Messaging API SDK for Python