input: def create_web_app():
      """Create a web application in Python using Flask that will take user input and generate an HTML page with the input.
      >>> create_web_app()
      // The function returns a Flask app object.
      """
output:     
      from flask import Flask, request, render_template_string
  
      app = Flask(__name__)
  
      @app.route('/', methods=['GET', 'POST'])
      def index():
          if request.method == 'POST':
              user_input = request.form['user_input']
              html_content = f"<h1>You entered: {user_input}</h1>"
              return render_template_string(html_content)
          return '''
              <form method="post">
                  <input type="text" name="user_input">
                  <input type="submit" value="Submit">
              </form>
          '''
  
      return app
  