Introduction to Plotly Dash (Python)

Building a simple Python Dash application involves a few basic steps. Dash is a great tool for making interactive web applications using Python, and it is especially powerful for creating data visualizations. Here’s a step-by-step guide to help you get started with your first Dash app.

1. Create a Project Folder

Open your command line interface (CLI) and run the following command to create a new directory for your project:

mkdir sample-dash-app
cd sample-dash-app

2. Set Up a Virtual Environment

It’s good practice to use a virtual environment for Python projects to manage dependencies. Use the following commands to create and activate a virtual environment:

# For Windows
python -m venv venv
.\venv\Scripts\activate

# For macOS and Linux
python3 -m venv venv
source venv/bin/activate

3. Install Dependencies

Install Dash and Plotly, which are the main libraries you will need. You might also want to install other packages depending on your needs:

pip install dash plotly

4. Create a requirements.txt File

To share your project with others, it’s helpful to create a requirements.txt file which lists all of the packages that your project depends on. Run the following command to generate this file:

pip freeze > requirements.txt

5. Create the Dash Application

Create a new file named app.py in your project folder. You can do this via your text editor or the command line:

touch app.py # macOS and Linux
echo “” > app.py # Windows

Now, edit app.py to include the following complete Dash application code:

import dash
from dash import html, dcc
import plotly.express as px

app = dash.Dash(__name__)

app.layout = html.Div(children=[
html.H1(children=’Hello Dash!’),
html.Div(children=’’’Dash: A web application framework for Python.’’’),
dcc.Graph(
id=’example-graph’,
figure=px.bar(x=[“a”, “b”, “c”], y=[4, 1, 2], title=”Bar Plot Example”)
)
])

if __name__ == ‘__main__’:
app.run_server(debug=True)

Code Explanation

• Imports: The necessary modules from Dash and Plotly are imported.
• App Initialization: A new Dash app instance is created.
• Layout Definition: The app’s layout is defined using HTML and Plotly components. It includes a header (html.H1), a descriptive text (html.Div), and a simple bar graph (dcc.Graph).
• Running the Server: The if __name__ == '__main__': block checks if the script is executed as the main program and not imported as a module. The app.run_server method starts the app on the default Flask server.

6. Run the Application

Make sure your virtual environment is activated, and run your application with:

python app.py

Navigate to http://127.0.0.1:8050/ in your web browser to see your Dash application in action.

With these steps, you have created a basic but functional Dash application, set up a development environment properly, and prepared your project for easy sharing and collaboration.