Uploading Files from Flask to Another API

What will you learn?

Explore how to efficiently upload files received by your Flask application directly to an external API. This comprehensive guide equips you with the necessary knowledge and tools for seamless file handling and integration between services.

Introduction to the Problem and Solution

When developing web applications with Flask, managing user-uploaded files is a common requirement. At times, there arises a need to transmit these files from our server to an external API without storing them locally. While this task may seem complex due to multipart/form-data requests handling, fear not! We have a straightforward solution that combines the power of Python’s requests library with Flask’s request object.

Our approach involves capturing files from form submissions in our Flask app using request.files, which provides access to FileStorage objects. By utilizing the requests library’s ability to send multipart/form-data requests, we can efficiently upload these files directly to another API endpoint. This method streamlines workflow processes and conserves resources by eliminating the need for local storage.


from flask import request
import requests

@app.route('/upload-to-api', methods=['POST'])
def upload_file_to_external_api():
    if 'file' not in request.files:
        return 'No file part', 400

    file = request.files['file']

    files = {'file': (file.filename, file.stream, file.content_type)}

    external_api_url = 'https://external-api.com/upload'

    response = requests.post(external_api_url, files=files)

    if response.status_code == 200:
        return 'File successfully uploaded.', 200
        return f'Failed with status code: {response.status_code}', 500

# Copyright PHD


In this solution:

  1. Endpoint Creation: Establish an endpoint /upload-to-api for receiving POST requests containing files.
  2. Request Handling: Verify the presence of a “file” part in incoming POST requests using request.files.
  3. Preparing File Data: Construct a suitable format for HTTP upload by organizing data into Python dictionaries with essential metadata like filename and content type.
  4. Performing Request: Utilize requests.post to send prepared data (files) along with any required headers directly.
  5. Handling Response: Based on the status code received from the target API, return appropriate success or failure responses.

This direct interaction approach between services eliminates intermediary steps like local storage or additional processing layers that could introduce complexity or latency.

  1. How do I install necessary requirements?

  2. A: Ensure Flask and Requests are installed using pip: pip install Flask requests.

  3. What is multipart/form-data?

  4. A: It’s an encoding type used for submitting forms containing binary data (e.g., images/files) efficiently over HTTP.

  5. Can I include additional parameters during upload?

  6. A: Yes! Modify your files dictionary or utilize separate payload dictionaries based on your target API requirements.

  7. Is this method secure?

  8. A: While convenient, ensure your server only accepts authorized uploads and trust the destination API; consider encryption needs as well!

  9. Do I require special server permissions?

  10. A: Typically no extra permissions are needed beyond standard security considerations if Python can execute network calls outwardly.

  11. Can I test uploads without an actual external service?

  12. A: Yes! Tools like Postman Mock Server or httpbin.org offer ways to simulate endpoints during development/testing phases.


Effortlessly uploading files from your Flask application directly to another web service doesn’t have to be daunting. By leveraging Python libraries effectively, you can simplify processes and focus on business logic rather than technical intricacies related to inter-service communication and file transfers. This streamlined approach enhances efficiency significantly, making it a valuable asset within developer communities worldwide.

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