给我后端代码和爬虫程序

好的，以下是一个示例的后端代码和爬虫程序，使用Python Flask框架和Requests库实现：

后端代码：

from flask import Flask, jsonify, request
import threading
import time
import requests

app = Flask(__name__)

@app.route("/api/price")
def get_price():
    keyword = request.args.get("keyword")
    platform = request.args.get("platform")
    if platform == "taobao":
        url = "https://s.taobao.com/search?initiative_id=tbindexz_20170306&ie=utf8&search_type=item&tfsid=TB1rJ2vXNj1gK0jSZFuXXXn0XXa&sort=sale-desc&app=detailproduct&fs=1&cps=yes&cat=50005998&imgfile=&q=" + keyword
        headers = {
            "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36"
        }
        r = requests.get(url, headers=headers)
        r.encoding = "utf-8"
        data = r.text
        # 处理数据，获取价格信息等
        # ...
        # 返回数据
        return jsonify({
            "avg_price": avg_price,
            "max_price": max_price,
            "min_price": min_price,
            "date": date,
            "price": price
        })
    elif platform == "jingdong":
        # 类似地处理京东平台的数据
        # ...
    elif platform == "pinduoduo":
        # 类似地处理拼多多平台的数据
        # ...
    else:
        return "不支持的平台"

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=5000)

该示例代码使用Flask框架实现了一个简单的API接口，接收前端页面传来的商品关键字和平台选择信息，然后调用相应的爬虫程序获取价格信息并返回给前端页面。需要注意的是，该示例代码只是一个简单示例，需要根据实际需求进行修改和完善。

爬虫程序：

import requests
from bs4 import BeautifulSoup

def crawl_taobao(keyword):
    url = "https://s.taobao.com/search?initiative_id=tbindexz_20170306&ie=utf8&search_type=item&tfsid=TB1rJ2vXNj1gK0jSZFuXXXn0XXa&sort=sale-desc&app=detailproduct&fs=1&cps=yes&cat=50005998&imgfile=&q=" + keyword
    headers = {
        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36"
    }
    r = requests.get(url, headers=headers)
    r.encoding = "utf-8"
    data = r.text
    soup = BeautifulSoup(data, "html.parser")
    items = soup.find_all("div", class_="item J_MouserOnverReq  ")
    avg_price = 0
    max_price = 0
    min_price = 0
    date = []
    price = []
    for item in items:
        title = item.find("a", class_="J_ClickStat").text.strip()
        price_str = item.find("div", class_="price g_price g_price-highlight").text.strip().replace("¥", "")
        price_num = float(price_str)
        avg_price += price_num
        if price_num > max_price:
            max_price = price_num
        if min_price == 0 or price_num < min_price:
            min_price = price_num
        date.append(title)
        price.append(price_num)
    if len(items) > 0:
        avg_price /= len(items)
    return (avg_price, max_price, min_price, date, price)

# 类似地实现京东和拼多多平台的爬虫程序
# ...

if __name__ == "__main__":
    print(crawl_taobao("手机"))

该示例代码实现了一个简单的淘宝平台爬虫程序，接收商品关键字作为参数，然后爬取淘宝平台上的商品价格信息并返回。需要注意的是，该示例代码只是一个简单示例，需要根据实际需求进行修改和完善，同时需要遵守爬虫协议，避免对网站造成影响。