Serving Static Files

3.7. Serving Static Files#

In web development, static files refer to resources like images, CSS files (for styling), and JavaScript files (for interactivity) that don’t change as users interact with the web page. Flask makes serving static files easy by automatically creating a special route for these files.

3.7.1. Flask Project Structure#

To understand how Flask serves static files, it’s important to understand Flask’s project structure. Here’s a typical structure for a Flask project that includes static files:

/my_flask_app
    /static
        /css
            styles.css
        /images
            logo.png
    app.py

/static/: This directory contains all the static files like CSS, images, and JavaScript.
app.py: This is your main Flask application file, where you define your routes.

3.7.2. The static directory#

Flask knows that web applications often need static resources like images and stylesheets, so it automatically serves any files placed in a folder named static. By default, Flask creates a special route /static/ to serve these files.

For example, if you have an image called logo.png in the static directory, you can access it in your browser by visiting http://127.0.0.1:5000/static/logo.png. Flask automatically knows where to find it!

Changing the static URL#

By default, Flask serves static files under the /static/ URL path. However, you can change this URL path if you want to serve static files from a different location. For example, you might want to serve your files from /assets/ instead of /static/.

To do this, you can pass the static_url_path argument when creating the Flask application:

app = Flask(__name__, static_url_path='/assets')

3.7.3. Example: Serving CSS#

Let’s create a simple example where we serve a custom CSS file to style the homepage.

Create the Flask app (app.py)

from flask import Flask, render_template

app = Flask(__name__)

@app.route("/")  # Define the route for the home page
def home():
    return """
    <html>
    <head>
        <link rel="stylesheet" type="text/css" href="/static/css/styles.css">  <!-- Link to the CSS file -->
    </head>
    <body>
        <h1>Welcome to My Styled Homepage!</h1>
        <p>This page is styled with custom CSS.</p>
    </body>
    </html>
    """

if __name__ == "__main__":
    app.run(debug=True)

In this code:

We created a basic Flask app with a single homepage route.
In the <head> section of the HTML, we link to a custom CSS file located at /static/css/styles.css. The href points to the CSS file in the static folder.

Create the static/css/styles.css file

Next, we create the CSS file that will style our page. Place this file in the static/css/ folder.

body {
    background-color: lightblue;
    font-family: Arial, sans-serif;
}

h1 {
    color: darkblue;
}

p {
    color: darkgreen;
}

This CSS file changes the background color of the page to light blue, the heading (h1) to dark blue, and the paragraph text (p) to dark green.

Hint

Make sure your project folder looks like the following:

/my_flask_app
    /static
        /css
            styles.css
    app.py

Run the Flask App

python app.py

Access the Webpage

Open your browser and go to http://127.0.0.1:5000/. You should see the styled homepage with a light blue background, a dark blue heading, and dark green text for the paragraph. Flask automatically serves the CSS file from the /static/ folder.

3.7.4. Example: Serving Images#

Now that you’ve learned how to serve CSS files, let’s add an image to the homepage, such as a selfie, and serve it using Flask.

Update the Flask app (app.py)

from flask import Flask

app = Flask(__name__)

@app.route("/")  # Define the route for the home page
def home():
    return """
    <html>
    <head>
        <link rel="stylesheet" type="text/css" href="/static/css/styles.css">  <!-- Link to the CSS file -->
    </head>
    <body>
        <h1>Welcome to My Styled Homepage!</h1>
        <p>This page is styled with custom CSS.</p>
        <img src="/static/images/selfie.jpg" alt="My Selfie" width="300">  <!-- Serve the selfie image -->
    </body>
    </html>
    """

if __name__ == "__main__":
    app.run(debug=True)

In this code:

The <img> tag is used to display an image. The src attribute points to the image file selfie.jpg located in the static/images/ folder.
The width attribute sets the width of the image to 300 pixels (you can change it based on your ego).

Add the Image File

Place your selfie image in the static/images/ folder. You can name the file selfie.jpg or any name you prefer, as long as the file path matches what’s in the <img> tag.