A best approach to a creating specified http post body

[dzawer at gmail.com]

Hi all, I'm rather new to python but not exaclty without  programming
experience and not quite get  best pyhton practices.
I have a following problem that it seems I cannot find a way to solve
correctly.

I need to build a special http post body that consists of :
name=value +\r\n strings.
Problem is that depending on operations the number of  name,value
pairs can increase and decrease.
Values need to be initialized at runtime, so storing premade text
files is not possible.

The worst thing that some operations must be at beginning, so
dictionary approach with classes  is kinda out.

Could you please provide some examples or descriptions on how you
would solve such problem ?
Thanks in advance.