this is my code

 @app.route('/retrieveCustomers', methods=['GET', 'POST']) def retrieve_customers(): customers_dict = {} db = shelve.open('customer.db', 'r') customers_dict = db['Customers'] db.close() customers_list = [] for key in customers_dict: customer = customers_dict.get(key) customers_list.append(customer) if request.method == 'POST': sort_by = request.form['sort_by'] gender = request.form['gender'] if sort_by == 'region': customers_list = sorted(customers_list, key=lambda x: x.get_region()) elif sort_by == 'gender': customers_list = [customer for customer in customers_list if customer.get_gender() == gender] return render_template('retrieveCustomers.html', count=len(customers_list), customers_list=customers_list) @app.route('/updateUser//', methods=['GET', 'POST']) def update_user(id): update_user_form = CreateUserForm(request.form) if request.method == 'POST' and update_user_form.validate(): users_dict = {} db = shelve.open('user.db', 'w') users_dict = db['Users'] user = users_dict.get(id) user.set_first_name(update_user_form.first_name.data) user.set_last_name(update_user_form.last_name.data) user.set_gender(update_user_form.gender.data) db['Users'] = users_dict db.close() return redirect(url_for('retrieve_users')) else: users_dict = {} db = shelve.open('user.db', 'r') users_dict = db['Users'] db.close() user = users_dict.get(id) update_user_form.first_name.data = user.get_first_name() update_user_form.last_name.data = user.get_last_name() update_user_form.gender.data = user.get_gender() return render_template('updateUser.html', form=update_user_form) @app.route('/updateCustomer//', methods=['GET', 'POST']) def update_customer(id): update_customer_form = CreateCustomerForm(request.form) if request.method == 'POST' and update_customer_form.validate(): customers_dict = {} db = shelve.open('customer.db', 'w') customers_dict = db['Customers'] customer = customers_dict.get(id) customer.set_first_name(update_customer_form.first_name.data) customer.set_last_name(update_customer_form.last_name.data) customer.set_gender(update_customer_form.gender.data) customer.set_email(update_customer_form.email.data) customer.set_date_joined(update_customer_form.date_joined.data) customer.set_region(update_customer_form.region.data) customer.set_address(update_customer_form.address.data) db['Customers'] = customers_dict db.close() return redirect(url_for('retrieve_customers')) else: customers_dict = {} db = shelve.open('customer.db', 'r') customers_dict = db['Customers'] db.close() customer = customers_dict.get(id) update_customer_form.first_name.data = customer.get_first_name() update_customer_form.last_name.data = customer.get_last_name() update_customer_form.gender.data = customer.get_gender() update_customer_form.email.data = customer.get_email() update_customer_form.date_joined.data = customer.get_date_joined() update_customer_form.region.data = customer.get_region() update_customer_form.address.data = customer.get_address() return render_template('updateCustomer.html', form=update_customer_form) @app.route('/deleteUser/', methods=['POST']) def delete_user(id): users_dict = {} db = shelve.open('user.db', 'w') users_dict = db['Users'] users_dict.pop(id) db['Users'] = users_dict db.close() return redirect(url_for('retrieve_users')) @app.route("/logout") def logout(): return redirect(url_for('login')) @app.route('/deleteCustomer/', methods=['POST']) def delete_customer(id): customers_dict = {} db = shelve.open('customer.db', 'w') customers_dict = db['Customers'] customers_dict.pop(id) db['Customers'] = customers_dict db.close() return redirect(url_for('retrieve_customers')) if __name__ == '__main__': app.run(port=4996) 

the is my html for retrieveCustomer

{% extends "base.html" %} {% block title %}Library Loan System - Retrieve Customers{% endblock %} {% block content %} 
Retrieve Customers
 
 {% if count == 0 %} 
There are no customers.
 {% elif count == 1 %} 
There is 1 customer.
 {% else %} 
There are {{ count }} customers.
 {% endif %} 
  
 
 Sort by Region:  All North South East West   
 
  
 
 Sort by Gender:  All Male Female   
 
 
  {% for customer in customers_list %}  {% endfor %} 
 
 
 
User ID
 
Customer ID
 
First Name
 
Last Name
 
Gender
 
Email
 
Date Joined
 
region
 
Address
 
 
 
 
 
 
{{ customer.get_user_id() }}
 
{{ customer.get_customer_id() }}
 
{{ customer.get_first_name() }}
 
{{ customer.get_last_name() }}
 
{{ customer.get_gender() }}
 
{{ customer.get_email() }}
 
{{ customer.get_date_joined() }}
 
{{ customer.get_region() }}
 
{{ customer.get_address() }}
 
Update
 
 
     
 
 
  
 
Delete Confirmation
  
  
 Are you sure you want to delete {{customer.get_first_name()}} {{customer.get_last_name()}}? 
  
   
 
 
 
 
 
 
 
 
 {% endblock %} 

this is my code i want sort the customer based on gender and region when i tried to code it shows error

Internal Server Error

The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.

this is my pycharm error

127.0.0.1 - - [03/Feb/2023 21:54:13] "GET / HTTP/1.1" 200 - [2023-02-03 21:54:16,749] ERROR in app: Exception on /retrieveCustomers [GET] Traceback (most recent call last): File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\flask\app.py", line 2525, in wsgi_app response = self.full_dispatch_request() File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\flask\app.py", line 1822, in full_dispatch_request rv = self.handle_user_exception(e) File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\flask\app.py", line 1820, in full_dispatch_request rv = self.dispatch_request() File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\flask\app.py", line 1796, in dispatch_request return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args) File "C:\Users\praka\PycharmProjects\simpleweb\__init__.py", line 97, in retrieve_customers return render_template('retrieveCustomers.html', count=len(customers_list), customers_list=customers_list) File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\flask\templating.py", line 146, in render_template template = app.jinja_env.get_or_select_template(template_name_or_list) File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\jinja2\environment.py", line 1081, in get_or_select_template return self.get_template(template_name_or_list, parent, globals) File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\jinja2\environment.py", line 1010, in get_template return self._load_template(name, globals) File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\jinja2\environment.py", line 969, in _load_template template = self.loader.load(self, name, self.make_globals(globals)) File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\jinja2\loaders.py", line 138, in load code = environment.compile(source, name, filename) File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\jinja2\environment.py", line 768, in compile self.handle_exception(source=source_hint) File "C:\Users\praka\PycharmProjects\simpleweb\venv\lib\site-packages\jinja2\environment.py", line 936, in handle_exception raise rewrite_traceback_stack(source=source) File "C:\Users\praka\PycharmProjects\simpleweb\template etrieveCustomers.html", line 17, in template

jinja2.exceptions.TemplateSyntaxError: Encountered unknown tag 'url_for'. Jinja was looking for the following tags: 'endblock'. The innermost block that needs to be closed is 'block'. 127.0.0.1 - - [03/Feb/2023 21:54:16] "GET /retrieveCustomers HTTP/1.1" 500 -

pls help me trouble shoot my code and help with the solution