I found the quoted text in Programming Python 3rd edition by Mark Lutz from Chapter 16: Server-Side Scripting (page 987):

Forms also include a method option to specify the encoding style to be used to send data over a socket to the target server machine. Here, we use the post style, which contacts the server and then ships it a stream of user input data in a separate transmission. An alternative get style ships input information to the server in a single transmission step, by adding user inputs to the end of the URL used to invoke the script, usually after a ? character (more on this soon).

I read this with some puzzlement. As far as I know post data is sent in the same transmission as a part of the same http header. I have never heard of this extra step for post data transmission.
I quickly looked over the relevant HTTP rfc's and didn't notice any distinction in version 1.0 or 1.1. I also used wireshark for some analysis and didn't notice multiple transmissions for post.
Am I missing something fundamental or is this an error in the text?
Simple POST request is in single step. but when you are uploading a file, than the form is posted in multiple parts. In that case, the content type  application/x-www-form-urlencoded is changed to multipart/form-data.
HTTP POST Requests require multiple transmissions?