app.py

from flask import Flask, request, flash, url_for, redirect, render_template
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///students.sqlite3'
app.config['SECRET_KEY'] = "random string"

db = SQLAlchemy(app)

class students(db.Model):
   id = db.Column('student_id', db.Integer, primary_key = True)
   name = db.Column(db.String(100))
   city = db.Column(db.String(50))
   addr = db.Column(db.String(200)) 
   pin = db.Column(db.String(10))

   def __init__(self, name, city, addr, pin):
      self.name = name
      self.city = city
      self.addr = addr
      self.pin = pin

with app.app_context():
   db.create_all()

@app.route('/')
def show_all():
   return render_template('show_all.html', students = students.query.all() )

@app.route('/new', methods = ['GET', 'POST'])
def new():
   if request.method == 'POST':
      if not request.form['name'] or not request.form['city'] or not request.form['addr']:
         flash('Please enter all the fields', 'error')
      else:
         student = students(name = request.form['name'], city = request.form['city'], addr = request.form['addr'], pin = request.form['pin'])
         db.session.add(student)
         db.session.commit()
         flash('Record was successfully added')
         return redirect(url_for('show_all'))
   return render_template('new.html')

@app.route('/edit/<int:id>', methods=['GET', 'POST'])
def edit(id):
    student = students.query.get_or_404(id)
    if request.method == 'POST':
        if not request.form['name'] or not request.form['city'] or not request.form['addr']:
            flash('Please enter all the fields', 'error')
        else:
            student.name = request.form['name']
            student.city = request.form['city']
            student.addr = request.form['addr']
            student.pin = request.form['pin']
            db.session.commit()
            flash('Record was successfully updated')
            return redirect(url_for('show_all'))
    return render_template('edit.html', student=student)

@app.route('/delete/<int:id>')
def delete(id):
    student = students.query.get_or_404(id)
    db.session.delete(student)
    db.session.commit()
    flash('Record was successfully deleted')
    return redirect(url_for('show_all'))

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