如何将变量传递给python flask应用程序？

from flask import Flask

app = Flask(__name__)

@app.route('/user/<username>')
def show_user(username):
    return 'User: {}'.format(username)

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

from flask import Flask, request

app = Flask(__name__)

@app.route('/login', methods=['POST'])
def login():
    username = request.form['username']
    password = request.form['password']
    # 进行登录验证等操作
    return 'Logged in as {}.'.format(username)

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

from flask import Flask, request

app = Flask(__name__)

@app.route('/search')
def search():
    keyword = request.args.get('keyword')
    # 进行搜索操作
    return 'Search keyword: {}'.format(keyword)

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

from flask import Flask, request, make_response

app = Flask(__name__)

@app.route('/set_cookie')
def set_cookie():
    response = make_response('Cookie is set.')
    response.set_cookie('username', 'john')
    return response

@app.route('/get_cookie')
def get_cookie():
    username = request.cookies.get('username')
    return 'Username: {}'.format(username)

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