I am learning perl and python... at the same time, not my by design but it has to be done.
Question:
In a perl script I use(see below) at the head of my txt.
There isn't really any equivalent. Python's design has evolved over time, and many changes have been made (particularly in 3.x) to make sure that the defaults in the language are what a developer wants by default. It's very rare for a feature to exist but be an optional flag.
This probably comes down to The Zen of Python's 'There should be one-- and preferably only one --obvious way to do it.' Python's design is focussed around readability, and having many ways of doing things or changing the way the language works makes code harder to read.
The closest, I would argue, is imports from __future__ in older versions of Python to introduce some fixes/new features from newer versions into older versions (such as division going from integer to float division by default). This is similar in the sense that it is improving the default behaviour to be more sensible in the standard case.
Edit: I seem to have attracted ire from perl users who see this post as an attack on Perl - it was never intended as such. Perl is a fine language, my original post just used poor wording and wasn't clear in it's explanation. I have attempted to clarify.