How to Get Uploaded File in Flask: Simple Guide

In Flask, you get an uploaded file using request.files inside your route function. Access the file by its form field name, for example, file = request.files['file'], then you can save or process it.

Syntax

Use request.files to access files sent by the client in a POST request. The key inside request.files matches the name attribute of the file input in the HTML form.

• request.files['file']: gets the uploaded file object.
• file.filename: the original filename on the client.
• file.save(path): saves the file to the server.

python

from flask import request

@app.route('/upload', methods=['POST'])
def upload():
    file = request.files['file']  # 'file' is the input field name
    filename = file.filename
    file.save(f'/path/to/save/{filename}')
    return 'File uploaded successfully'

Example

This example shows a simple Flask app with an HTML form to upload a file. The server receives the file and saves it to a folder named uploads.

python

from flask import Flask, request, render_template_string
import os

app = Flask(__name__)
UPLOAD_FOLDER = 'uploads'
os.makedirs(UPLOAD_FOLDER, exist_ok=True)

@app.route('/')
def index():
    return render_template_string('''
        <form method="POST" action="/upload" enctype="multipart/form-data">
            <input type="file" name="file">
            <input type="submit" value="Upload">
        </form>
    ''')

@app.route('/upload', methods=['POST'])
def upload():
    file = request.files.get('file')
    if file and file.filename:
        filepath = os.path.join(UPLOAD_FOLDER, file.filename)
        file.save(filepath)
        return f'File "{file.filename}" uploaded successfully.'
    return 'No file selected or empty filename.'

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

Output

Running the app and uploading a file shows: File "example.txt" uploaded successfully.

Common Pitfalls

• Not setting enctype="multipart/form-data" in the HTML form causes request.files to be empty.
• Using request.form instead of request.files to get files will not work.
• Trying to access a file key that does not exist raises a KeyError. Use request.files.get('file') to avoid this.
• Not checking if file.filename is empty can cause saving empty files.

python

from flask import request

# Wrong way (missing enctype and wrong access)
# HTML form without enctype="multipart/form-data" will not send files properly.

# Right way
file = request.files.get('file')
if file and file.filename:
    file.save('/path/to/save/' + file.filename)

Quick Reference

Remember these key points when handling file uploads in Flask:

• Use request.files['fieldname'] to get the file.
• Set enctype="multipart/form-data" in your HTML form.
• Check if the file exists and has a filename before saving.
• Save files securely to avoid overwriting or security risks.

Key Takeaways

Use request.files with the form input name to get uploaded files in Flask.

Always set enctype="multipart/form-data" in your HTML form for file uploads.

Check if the file exists and has a valid filename before saving.

Use file.save(path) to store the uploaded file on the server.

Use request.files.get() to avoid errors if the file key is missing.