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Python and Flask Workshop

Welcome to the python-flask-app repo. Today we will be building the image and running the container for Python and Flask, which can be found in this repo. But in order to make this general app your own, we will need to learn more about Github.

You will use Flask to build a web application to interact with your MariaDB servier.

Prerequisites

  1. Create a free github user account - https://github.com/join?plan=free&source=pricing-card-free
  2. Install SublimeText or Textmate for Mac for syntax coloring (or editor of your choosing)

Github Primer

  1. Complete the Github hello-world activity linked to above: https://guides.github.com/activities/hello-world/

Create your final project webapp

  1. From the https://github.com/munners17/python-flask-app repo, click the Use this template button
  2. Name the repo after a webapp name related to your final project
  3. Choose a private repo!
    Note: Feel free to make your project repo public after projects have been turned in
  4. Clone your newly created repo using your method of choice.

Review the Dockerfile

A Dockerfile is just a text file that that contains all the commands, in order, for building a specific docker image. The Docker Engine will automatically build the image when running the docker build command. For the class project, you may have to edit the Dockefile if you have additional dependencies.

Some basic Dockerfile commands are:

  • FROM: Identifies the base application of the image. A Dockerfile must start with a FROM instruction.
  • RUN: Install any dependencies
  • WORKDIR: Sets the working directory other commands will work from
  • CMD: Sets the command to be executed when running a container based on this image (not when the image is being built). This in essence identifies the application the container is encapsulating.
  • COPY: Adds files from your Docker client’s current directory.

Note we are not COPYING python files into the container. Instead we will create a mount point that will allow the webapp/ subfolder on your host (inside this repo) to be shared inside the container, similar to a network mount.

Build and Start Flask Container

  1. On the command line, move to your previously cloned repo
    • cd path/to/repo
  2. Build the docker image docker build -t munners17/python-flask .
  3. Create a docker network to allow different docker containers to easily communicate with each other over an IP network. Then bind the existing mariadb container to the newly created network bridge.
    • docker network create --driver=bridge db-network
    • docker network connect db-network mariadb-diveshop
  4. Create and run the container, connecting it to the shared network, db-network
    • docker run --name python-app -p 5000:5000 --mount type=bind,source="${PWD}"/webapp,target=/app --net db-network munners17/python-flask
    • Remember docker run CREATES AND STARTS the container. When needing to start the container in the future, use docker start -a python-app, since it does not need to be re-created.
  5. Verify the container is Up by checking the STATUS column after executing docker ps in another terminal

Login to your Flask Container

  1. Use docker exec to start an interactive session inside the container and run the bash shell to access the terminal. Command to login: docker exec -it python-app bash
  2. Start python and run a few python commands. Hit after each of the following:
  • python3
  • 4 + 3
  • x = [1, 2, 3, 4, 5]
  • print(x)
  • exit()

Depending on your skill level, you may want to walk through this introduction: https://www.w3schools.com/python/python_intro.asp

Flask Workshop

Update Existing Web App

You will find a basic implementation of the Flask web application framework in webapp/index.py. The python container is currently running index.py. See what index.py is doing by navigating to http://localhost:5000/

[CHANGE ME] should appear in your browser window.

You may have noticed we have not started a Web Server to handle the HTTP traffic from our web app to the browser! Well, Flask is being run in Developmemnt mode which launces its own local web server for testing purposes - this is the web server serving your browser client right now. This is not recommended for a Production environment.

Also notice in index.py that debug=True when running the Flask object. This enables the debugger and also allows the server to reload whenever it detects a code change. Try it out by starting to build out your web application:

  1. Use Sublime Text or a text editor of your choice to edit the index.py and replace "[CHANGE ME!] with "Hello World!":
from flask import Flask
app = Flask(__name__)
 
@app.route("/")
def hello():
   return "Hello World!"
 
if __name__ == "__main__":
   app.run(host="0.0.0.0",debug=True)

Open http://localhost:5000/ in your web browser, and “Hello World!” should appear without having to restart the application.

Creating URL routes

URL routing make URLs in your Web app easy to remember and organize. Use the @route() decorator to bind functions to a specific URL. The function will be called when the URL is accessed by the browser.

We will now create some URL routes:

  • /destinations
  • /customers/
  • /members/name/

Replace the code in index.py with the code below

from flask import Flask, render_template, request, redirect
app = Flask(__name__)
 
@app.route("/")
def index():
   return "Index!"
 
@app.route("/destinations")
def dest():
   return "Destinations!"
 
@app.route("/customers")
def customers():
   return "Customers"
 
@app.route("/customers/<string:name>/")
def getMember(name):
   return name
 
if __name__ == "__main__":
   app.run(host="0.0.0.0", debug=True)

Try the URLs in your browser:

Rendering HTML

Flask can generate HTML by referencing template files you locate in the /templates/ subdirectory. Use the render_template() function to call on the appropriate template and pass it any data you want to use or display.

Create a file named show_c.html in a new /templates/ subdirectory relative to where index.py is located (inside `/webapp/):

<html>
<head><title>INFO 257 workshop show data</title>
</head>

<h1> Hello {{customer}}</h1>

</body>
</html>

Edit the customers/<string:name> route in the Flask app to render the new template:

@app.route("/customers/<string:name>/")
def getMember(name):
   return render_template(
   'show_c.html',customer=name)

You can then open to see an HTML formatted page: http://127.0.0.1:5000/customers/Jackson/

Passing Data

The template HTML file can reference data passed by render_template() by utilizing a special syntax defined by the Jinja2 template engine. You implemented this in the step above by passing the name variable to show_c.html as the variable customer.

You can pass any data the python/flask app has access to, such as a local variable. Replace the /customers route in index.py:

@app.route("/customers")
def customers():
   name_local="Keith Lucas"
   return render_template('show_c.html',customer=name_local)

You can then open to see an HTML formatted page with the local variable passed: http://127.0.0.1:5000/customers

Task: Create a Template

  1. Create a new template file (show_d.html) that displays a Diveshop destination name of your choosing when accessing this URL: localhost:5000/destinations

Accessing the Database

Flask extends the SQLAlchemy library that allows for connecting to a database named : https://flask-sqlalchemy.palletsprojects.com/en/2.x/quickstart/

You will be able to execute SQL querires and receive the results programatically (similar to your DataGrip client).

Use the SQLALCHEMY_DATABASE_URI configuration of the Flask object to designate the location and credentials of your mariaDBMS and database name. Note the the docker containers can identify themselves over the Docker network using DNS where their address is .. In this case, our mariaDB container can be identified using mariadb-diveshop.db-network

First, update the web app to connect to your Diveshop database via SQLAlchemy. Replace the first 2 lines in index.py with the following:

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

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql+pymysql://root:mypass@mariadb-diveshop.db-network/Diveshop'
db = SQLAlchemy(app) 

@app.route("/database")
def datab():
   result = db.engine.execute("SELECT DATABASE()")
   names = [row[0] for row in result]
   return names[0]

Diveshop should be displayed when accessing : http://127.0.0.1:5000/database

List Customers in the Database

Edit the show_c.html template to display all the customers in Diveshop. Utilize the Jinja2 template syntax referenced above to loop through the customers passed by the flask app, creating a new HTML table row for each customer.

show_c.html:

<html>
<head><title>INFO 257 workshop show data</title>
</head>

<body>
	<table class="table">
		<tr>
			<th>Customer Name</th>
			<th>City</th>
			<th>State</th>
		</tr>
			{% for ui_row in customers %}
		<tr>
			<td>{{ ui_row.Cust_Name }}</td>
			<td>{{ ui_row.City }}</td>
			<td>{{ ui_row.State }}</td>
		</tr>
			{% endfor %}
	</table>
</body>
</html>

index.py::

Now query the database to select all customers (all rows in DIVECUST relation) in the web app and pass to rendering engine for show_c.html. Update the /customers URL:

@app.route("/customers")
def customers():
    result = db.engine.execute("select * from DIVECUST")
    names = []
    
    for row in result:
        name = {}
        name["Cust_Name"] = row[1]
        name["City"] = row[3]
        name["State"] = row[4]
        names.append(name)

    return render_template('show_c.html',customers=names)

The list of customers in Diveshop should be displayed when accessing: http://127.0.0.1:5000/customers

TASK: List Destinations

  1. Have all the Diveshop Destinations names and their travel cost display when accessing http://127.0.0.1:5000/destinations * Note: Copy+Paste from the Customers logic to allow you to just change the SQL query

Forms

Basic user input is handled by HTTP Forms.

Try letting the user hit a button to choose which list of records to return from the home page.

Create a new template: index.html:

<html>
<head>
 <title>INFO 257 Workshop Form</title>
 <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1">
</head>

<body>
 <br>
 
 <form method="POST" action="/customers">

   <div class="form-group">
     <input type="submit" value="List Customers" />
   </div>
 </form>
 
 <br>
 
 <form method="POST" action="/destinations">

   <div class="form-group">
     <input type="submit" value="List Destinations" />
   </div>
 </form>
 
</body>

</html>

TASK: List Customers and Destinations with Button Click

  1. Update index.py to render the new index.html at the root/home location: http://127.0.0.1:5000/ . You should see 2 new buttons
  • You should receive an error message declaring an unallowalbe method after clicking on the bugtton. To proceed, complete the next step:
  1. The HTTP POST method must be declared as an allowable request for the "destinatons/" and "customers/" routes (Note HTTP/GET is the default). Edit existing route parameters in index.py that the POST in index.html is linked with:
@app.route("/destinations", methods=["POST", "GET"])

@app.route("/customers", methods=["POST", "GET"])

Click the buttons on http://127.0.0.1:5000/ to confirm they produce the correct lists of data

Now try a text box to search the database. We will enter the Accomodation Type to return destinations that match that type (Expensive, Moderate, Cheap)

First add a text box form element that posts to the /destinations URL.

index.html: Add this form element after the last </form> tag

<br>
<form method="GET" action="/destinations">
	<label for="search">Find Destinations by Accomodation</label>
	<input id="search" name="search" class="form-control" type="text" /><br />
</form>

Now there are two form methods handled by the /destinations flask method. Produce different logic depending on the method issued:

index.py: Replace the beginning of the dest() method, everything before names = [], with the following logic. Note this may have to be update to integrate with the varialbe names you used in a previous Task that implemented this function():

if request.method == "GET":
    search = request.args.get('search')

    result = db.engine.execute("select * from DEST where Accomodations=%s",search)
else:
    result = db.engine.execute("select * from DEST")

Try it out by typing an Accomodation type into the text box @ http://127.0.0.1:5000/

Now a text box is not very friendly for matching an enumerated list of types, like Accomodation Type. Let's create a dropdown to allow the user to select from the available options.

index.html: Replace the GET form elements with the following which dynamically generates the dropdown options based on the data variable passed:

<form method="GET" action="/destinations">
	<label for="search">Find Destinations by Accomodation</label>
  	<select id="accomodations" name="accomodations">
  				
		    {% for ui_row in data %}
    		<option value="{{ui_row.Accomodations}}">{{ui_row.Accomodations}}</option>
	    	{% endfor %}
    	</select>
   	<input type="submit" value="Submit" />
</form>

Edit the flask route method for URL(/) to send the proper Accomodation type data to be displayed in the drop down button: index.py:

@app.route("/")
def index():
   result = db.engine.execute("select DISTINCT(Accomodations) from DEST")
   accs = []

   for row in result:
       name = {}
       name["Accomodations"] = row[0]
       accs.append(name)

   return render_template("index.html", data=accs)

Right-click the web page and select "View Source" to view the web page returned back from the server to your client (browser). Verify the HTML has been updated dynamically to include all the Accomodation options:

<form method="GET" action="/destinations">
			<label for="search">Find Destinations by Accomodation</label>
  			<select id="accomodations" name="accomodations">
  				
    			<option value="Cheap">Cheap</option>
    			
    			<option value="Moderate">Moderate</option>
    			
    			<option value="Expensive">Expensive</option>
    			
    		</select>
    		<input type="submit" value="Submit" />
		</form>

TASK: Capture dropdown value

  1. Edit the /destinations route method to capture the selected dropdown value to allow the proper Destinations to be displayed [Only requires editing one word]
  2. Verify proper destinations displayed after hitting submit button next to dropdown

Next Workshop

  1. HTML Styling