POST Multipart-Encoding does not work if the Content-Type header has been previously defined in the session

Hi,

I just wasted two hours because it seems that the POST Multiple Multipart-Encoded Files function does not work if a Content-Type has been previously defined at the session level.

Example:

...

session.headers.update({“Content-Type”: “application/json”})

...

response = session.post(
    “http://localhost:3000/api/v1/pipelines/upload”,
    files={
        “file”: (“hello_world3.py”, f, “text/x-python”)
    },
    data={
        “urlIdx”: “2”
    }
)

Two suggestions:

• a. Either modify the implementation of POST Multiple Multipart-Encoded Files to overwrite the content of the Content-Type header even if it has been defined at the session level
• b. Or issue a warning message to inform the developer of their possible error

What do you think?

Best regards,
Stéphane

Start by reproducing the example from the “POST Multiple Multipart-Encoded Files” documentation section, including a session-level Content-Type header, then trace how the session.post call prepares the multipart request. Determine the expected behavior for the conflicting header and verify it with a focused regression test or warning check; done means the behavior is documented and consistently tested.