Description about this project [while learning]

Reference : https://overiq.com/flask-101/

Live project link : https://blogsinflask.herokuapp.com/

What is flask ?

• Flask is a micro framework for Python, meaning it's small and doesn't have large no. of built in modules like in other frameworks like Django or Grails. Flask is also less rigid about how you should structure your application.Unlike framework like Django, where you have to follow the strict rules. In Flask, you are free to structure your application the way you want.

Create virtual environment in python

• Isolate the packages in this project from the global environment
• to create virtual environment in python, we use virtualenv command as virtualenv venv in project directory, where venv is the name of virtual environment [user friendly name]
• to install virtualenv on mac use pip install virtualenv
• to activate virtualenv run source venv/bin/activate and to deactivate use deactivate

To install Flask inside virtual environment

• To install Flask inside virtual environment enter the command: sudo pip3 install flask or pip3 install flask on project directory not venv dir or pip install flask==version_number if specific version.
• to unistall if needed, use python3 -m pip uninstall flask
• to verify flask installation we can use following command, it will give the installed version of the flask [2.1.2] as of writing this file
• import flask
• print(flask.__version__)

init.py , load app & run app

• The init.py file makes Python treat directories containing it as modules.
• Furthermore, this is the first file to be loaded in a module, so you can use it to execute code that you want to run each time a module is loaded, or specify the submodules to be exported.

run app

• To run app either use python main_file.py or flask run

Define route

• to define route in flask , we can use app.add_url_rule('/', 'index', index) where index is the name of the method or use route decorator as @app.route('/')

Blueprint

• to separate route from the main app, we can create blueprint and later register to that main file in init.py
• create blueprint as auth = Blueprint('auth', __name__) # define blue print where Blueprint is imported from flask
• register blue print as : '.views' is the name of blueprint

       from .auth import auth
  

• contains all the route
• define as blue print i.e tell that it contains bunch of routes

Can have html files in template folder [templates is default]

• Can render html page when request [/, / some patters ] using render_template method as render_template('file_name_in_templates foler', data if any) for eg : return render_template('home.html', title='My Blogs - Powered with flask !')

• To pass many arguments data to the view , use as

    template_context = dict({home_nav_text = home_nav_text, blogs_nav_text = blogs_nav_text,admin_login_nav_text=admin_login_nav_text,search_nav_text=search_nav_text })
    return render_template('home.html', **template_context)
  

  or create dictionary and pass

    data = {
      'title' : 'My blogs in flask',
      'home_nav_text' : 'Home'
       # more field
    }
    return render_template('home.html', **data)
  

Creating response

• Even though flask autmatically creates reposne using make_response() , but often we need to include more options like header , content-type etc,
• syntax of make_response is res_obj = make_response(res_body, status_code=200)
• to set additional type , we can use res_obj as res.headers['Content-Type'] = 'text/plain' res.headers['Server'] = 'Foobar '

Redirect the reponse

• to redirect the response, we can use return redirect("url_to_redirect", code=301)
• To include template from one file or directory in another we can use , include statement in flask as {% include 'path/to/template' %}

Intercepting requests

• Just like grails [& other langaguages too] has interceptor, python also some decorators like before_first_request, after_request etc can be used as

@app.before_request
def before_request():
    print("before_request() called")

Aborting requests

    def abort_this_request():
          abort(404)

serving static files

• static files like .css , .js files are included in 'flask_app/static' directory by default , if different, have to configure.
• to use that files, use <link rel="stylesheet" href="{{ url_for('static', filename='nav_styles.css') }}">

custom error handler

• have errorhandler decorator to show custom pages
• can be used as @app.errorhandler(404) where 404 is the code passed to indicate not found

connecting to database

• without using ORM tools
• There are several python modules that allow us to connect to and manipulate the database using PostgreSQL, one of them is Psycopg2
• To install Psycopg2, we can run the command sudo pip3 install psycopg2
• once installed, we can import it and get various available methods.

To share [Extract required dependencies in requirements.txt file]

• use command in project directory pip freeze > requirements.txt

Deploy to heroku

• Create account & login to heroku
• heroku login
• Install heroku CLI
• install dependency called gunicorn as pip3 install gunicorn The Gunicorn "Green Unicorn" is a Python Web Server Gateway Interface HTTP server.
• create Procfile and web: gunicorn main:app [ this creates server and tell heroku what to do with our file] main.py has app to run
• git init & commit
• create heroku app from CLI as heroku create blogsinflask , blogsinflask is app name
• git remote -v gives remote repository
• push to heroku git push heroku main