requests library seems to ignore "Transfer-Encoding" header

[Green360]

I wanted to send a request with "Transfer-Encoding:chunked" but somehow the header is never set.
Below is my code for testing and the corresponding captured request.

import requests

url = 'http://[replaced]/test.php'

def data_chunks():
    yield b'7\r\n'
    yield b'param=2\r\n'

response = requests.post(url,data=data_chunks(), headers={"Transfer-Encoding":"chunked", "Content-Type":"application/x-www-form-urlencoded"}, proxies={"http":"http://127.0.0.1:8080"})

POST /test.php HTTP/1.1
Host: [replaced]
User-Agent: python-requests/2.28.1
Accept-Encoding: gzip, deflate, br
Accept: /
Connection: close
Content-Length: 12

7
param=2

If I do not set the "Transfer-Encoding" header it is not used and even if I explicitly set the "Transfer-Encoding" header it is not used. The requests library always seems to put a "Content-Length" instead.
My goal is to form this request:

POST /test.php HTTP/1.1
Host: [replaced]
Transfer-Encoding: chunked
Content-Type: application/x-www-form-urlencoded

7
param=2

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