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How to download files in Flask

Downloading files from Flask applications

Flask allows downloads, just like JavaScript-based web applications do.

There are two components to this process.

HTML

There needs to be an HTML href, which will call the appropriate Python function for the download.

<a href="{{ url_for('download', filename="downloadFile.txt") }}">File</a>

Python

The Python component will consist of a function that will return the required file to the client.

@app.route('/uploads/<path:filename>', methods=['GET', 'POST'])
def download(filename):
    # Appending app path to upload folder path within app root folder
    uploads = os.path.join(current_app.root_path, app.config['UPLOAD_FOLDER'])
    # Returning file from appended path
    return send_from_directory(directory=uploads, filename=filename)

This function takes the required file’s name as an argument. It then uses the os module’s path.join function to append the Flask app’s root path stored in current_app.root_path and the upload folder’s path from the root folder stored in app.config['UPLOAD_FOLDER'].

current_app is the application context. It can be used wherever an application context has been set up. app.config is a dictionary that stores a number of variables assigned by Flask itself or by the programmer. The UPLOAD_FOLDER variable has to be set up by the user.

From the appended path, the function returns the file found by send_from_directory, which takes the folder path in the first parameter and the file name in the second parameter.

Remember that you need to have access to the file you are downloading.

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