Hello Coders,
This article aims to help beginners to accommodate with Flask, the popular web framework written in Python. To follow and learn something from this tutorial there is no need to have a previous programming background, the content will be presented in the most simple way possible, enhanced at some point with visual materials.
By Moez Ali, Founder & Author of PyCaret. RECAP In our last post, we demonstrated how to develop a machine learning pipeline and deploy it as a web app using PyCaret and Flask framework in Python.If you haven’t heard about PyCaret before, please read this announcement to learn more. In this tutorial, we will use the same machine learning pipeline and Flask app that we built and deployed. Sep 26, 2016 Basically, the Flask app is pulling a Bokeh session, that’s running on the same machine, and serving it to the web. The problem is that the Bokeh app is served with ‘http’ and not ‘https’, which causes the browser to reject it. I assume that the solution lies in the Nginx config file, or the Flask app itself.
This tutorial will be periodically updated with new topics based on the new technology trends and your suggestions. Thank for reading!.
Python is an interpreted programming language (no compilation phase as for C/C++ programs) with high-level built-in data structures quite attractive for Rapid Application Development. The Python interpreter along with the standard libraries are available in source or binary form all major platforms (Linux, Windows or Mac).
To execute a Python program we need to have the Python interpreter available in the terminal. The first step is to access the official download page, download the installer for our operating system (Mac, Linux, M$ Windows) and execute it. If the installation goes well we should be able to access the interpreter from the terminal window (Powershell for windows, Xterm for Linux ..).
Please install the Python 3.x version, Python 2.x is deprecated and no longer supported by the Python foundation.
Flask is a Python web framework built with a small core and modularity in mind. It is classified as a microframework because it does not require particular tools or libraries. It has no database abstraction layer, form validation, or any other components, and all those super necessary features are provided by third-party libraries developed by the team behind Flask or other developers from the community.
The best definition I've found is this: Web framework is a set of components and libraries designed to simplify your web development process. - Source HackerNoon.
Indeed, the goal of a Web Framework is to make our life easier and provide help regarding the repetitive configuration and modules required by multiple projects. Flask does this flawlessly.
A short and curated list. Feel free to suggest more in the comments.
This section contains a few open-source UI-Ready starters already coded with a basic set of modules, helpers and deployment scrips.
For more open-source admin dashboards please access the AppSeed platform. The source code is published under the MIT license on Github (no account required to use the code).
The most easier way to install Flask is to use PIP (python package manager), which comes with Python3 binary distribution.
To check the installation, we can open the python CLI and import flask. If the module is properly installed, we should see no errors after import.
Each project has a list of dependencies usually saved in requirements.txt file, located in the root of the project. This is a common practice visible in many opensource projects and adopted by many developers (me included). We can install the modules in two ways:
Virtual Environment - the recommended way. Using a Virtual Environment (aka VENV) the modules will be installed isolated in the workstation, usually called a sandboxed environment. A simple use case to visualize the benefit of a VENV.
Imagine that we have two apps that use different versions of Flask. If The dependencies are installed globally, the dependencies will affect the set up for the other app. To avoid this use case, a virtual environment helps the developer to execute the app using an isolated environment, and both apps are usable in the same time, without dependencies errors.
Create a VENV Unix based systems
Create a VENV for Windows OS
Once the VENV is created and activated, we can install the project requirements using PIP:
Flask uses third party libraries (or modules) to provide common features used in many projects. I will drop here a short-list with popular modules. Feel free to suggest more in comments, if I missed some.
migrate the old structure to the new one bu generating the necessary SQL and scripts. Flask Dashboard Black, the app we will use as a sample to see something nice on the screen, is an open-source product coded in Flask on top of a beautiful UI Kit provided by Creative-Tim agency.
The source is available on Github and anyone can download the code and use it for hobby or commercial projects. In case you have issues using it, AMA in the comments.
App Links
The build instructions (saved also in the README file) are listed below:
If all goes well, we should see the dashboard, up & running in the browser. Please note that the app redirects the guest users to the login screen. Please create a new user using the registration page and authenticate into the app. By default, the app uses SQLite to save login information, but we can switch to other databases like MySql or PostgresSQL with ease. Promise to document this in a separate article.
Flask Dashboard - User Profile Page
Flask Dashboard - User Registration Page
As mentioned, the app is released under the MIT license. Feel free to grab the code and add more features on top. A short-list with suggestions:
Adress field in the profile pageCoding an app in our environment is nice, but release it into the wild in the internet is super rewarding, especially if is the first project. To deploy LIVE a Flask app, we have many options that depend on the server and the platform we are using. /destiny-2-mac-app.html.
The most simple way IMO is to use the Heroku platform. Of course, we need an account on the platform, and also the Heroku CLI installed in our environment. Please find below the steps to deploy the Flask Dashboard Black on Heroku:
If all goes well, the app should be up & running. The database is automatically created and we just need to register a new user and log in.
This is not so user-friendly deployment method, but the app that we've mentioned as a sample comes with the necessary scripts to deploy the app instantly using Docker.
In case you want to fully understand the whole process behind the Docker deployment, feel free to access an article, entirely dedicated to this topic: Flask Dashboard - Execution with Docker. The basic steps are:
Get the code from Github, using Git
Start the app in Docker
Visit http://localhost:5005 in your browser. The app should be up & running.
The deployment is not an easy topic to be digested by a beginner, and I prefer to provide a sample 100% configured and hide the real complexity covered by some nice scripts. To explain the deployment options, we need a full article that presents the possible and recommended architectures.
For a particular deploy configuration, feel free to AMA in the comments. I'll be glad to help and provide an extra opinion.
Thanks for reading! Yours, with much respect!
In order to test Flask installation, type the following code in the editor as Hello.py
Importing flask module in the project is mandatory. An object of Flask class is our WSGI application.
Flask constructor takes the name of current module (__name__) as argument.
The route() function of the Flask class is a decorator, which tells the application which URL should call the associated function.
The rule parameter represents URL binding with the function.
The options is a list of parameters to be forwarded to the underlying Rule object.
In the above example, ‘/’ URL is bound with hello_world() function. Hence, when the home page of web server is opened in browser, the output of this function will be rendered.
Finally the run() method of Flask class runs the application on the local development server.
All parameters are optional
| Sr.No. | Parameters & Description |
|---|---|
| 1 | host Hostname to listen on. Defaults to 127.0.0.1 (localhost). Set to ‘0.0.0.0’ to have server available externally |
| 2 | port Defaults to 5000 |
| 3 | debug Defaults to false. If set to true, provides a debug information |
| 4 | options To be forwarded to underlying Werkzeug server. |
The above given Python script is executed from Python shell.
A message in Python shell informs you that
Open the above URL (localhost:5000) in the browser. ‘Hello World’ message will be displayed on it.
A Flask application is started by calling the run() method. However, while the application is under development, it should be restarted manually for each change in the code. To avoid this inconvenience, enable debug support. The server will then reload itself if the code changes. It will also provide a useful debugger to track the errors if any, in the application.
The Debug mode is enabled by setting the debug property of the application object to True before running or passing the debug parameter to the run() method.