Why Are My Python Requests File Uploads Failing, and How Can I Fix Them?

Uploading Files with Python Requests

When attempting to upload a file using the Python requests library, users may encounter situations where the file is not successfully received by the server. This can be frustrating, especially when other solutions lack the necessary insights to resolve the issue.

Understanding the Problem

In the specific instance described, the user was uploading a file via a form submission using the requests.post() method. Despite providing the correct file name and contents, the server was not recognizing the uploaded file. Instead, it reported that the uploaded file was empty.

The Solution

The key to resolving this issue lies in correctly specifying the parameters for the files and data arguments of the requests.post() method. When uploading a file, it is essential to specify a mapping of the file's name to its contents. In this case, the user was attempting to set both the files and data arguments.

The correct approach for uploading a file with Python requests is to use the files argument to specify the file's mapping. Here's an updated code snippet that fixes the issue:

import requests

url = 'http://nesssi.cacr.caltech.edu/cgi-bin/getmulticonedb_release2.cgi/post'
files = {'upload_file': open('file.txt', 'rb')}
values = {'DB': 'photcat', 'OUT': 'csv', 'SHORT': 'short'}

r = requests.post(url, files=files, data=values)

By placing the file mapping in the files argument, the requests library will automatically handle the multipart form submission, including setting the appropriate headers.

Handling Advanced Scenarios

In some cases, users may need further control over the file upload process. Python requests supports various options to customize the file mapping, including providing a filename and content type. For more complex scenarios, such as uploading the entire POST body from a file, the data argument can be used without the files argument.

Conclusion

By understanding the correct usage of the files and data arguments, users can successfully upload files using Python requests. This enables seamless integration of file uploads into automated scripts and programs.

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