app.py

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

app=Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI']='sqlite:///weather.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS']=False
app.config['SECRET_KEY']='thisisasecret'
db=SQLAlchemy(app)

class City(db.Model):
    id=db.Column(db.Integer,primary_key=True)
    name=db.Column(db.String(50),nullable=False)
def get_weather_data(city):
    url=f'http://api.openweathermap.org/data/2.5/weather?q={city}&units=imperial&appid=224808221c3526f7470583afe6da6749'
    r=requests.get(url).json()
    return r

@app.route('/',methods=['GET'])
def index_get():
    cities=City.query.all()
    url='http://api.openweathermap.org/data/2.5/weather?q={}&units=imperial&appid=224808221c3526f7470583afe6da6749'
    weather_data=[]
    for city in cities:

        r=get_weather_data(city.name)
        print(r)
        weather={
        'city' : city.name,
        'temperature' :r['main']['temp'] ,
        'description' : r['weather'][0]['description'],
        'icon' : r['weather'][0]['icon'],
            }
        weather_data.append(weather)
    return render_template('weather.html',weather_data=weather_data)

@app.route('/',methods=['POST'])
def index_post():
    err_msg=''
    new_city=request.form.get('city')
    if new_city:
        existing_city=City.query.filter_by(name=new_city).first()
        if not existing_city:
            new_city_data=get_weather_data(new_city)
            if new_city_data['cod']==200:
                new_city_obj=City(name=new_city)
                db.session.add(new_city_obj)
                db.session.commit()
            else:
                err_msg='City does not exist in the world!'
        else:
            err_msg='City already added'
    if err_msg:
        flash(err_msg,'error')
    else:
        flash('City added successfully!')
    return redirect(url_for('index_get'))

@app.route('/delete/<name>/')
def delete_city(name):
    city=City.query.filter_by(name=name).first()
    db.session.delete(city)
    db.session.commit()
    flash(f'Successfully deleted {city.name}','success')
    return redirect(url_for('index_get'))
    return f'Deleted {name}'