While you can manipulate Python's AST, you can't do it in a way that looks like adding new syntax.
In Clojure you can write a list comprehension as `(for [x (range 10)] x)`. In Python you can write it as `[x for x in range(10)]`.
Imagine these didn't exist, and you wanted to implement them yourself.
In Clojure this is possible. Its list comprehensions are implemented as a Clojure macro: https://github.com/clojure/clojure/blob/b98ba84/src/clj/cloj...
In Python there are several problems. The first is that you can't easily pull the decorator trick on arbitrary expressions. Not even with a lambda function, at least without doing a lot of work - inspect.getsource doesn't handle those properly.
But let's lower the bar, and replicate `l = [x for x in range(10)]` instead. You can do that with a decorator and an ordinary function.
Then the problem becomes that you can only use existing syntax in the function body. Syntax that already means something else. If you put an ordinary list comprehension in the function body then you get a syntax error when the file is parsed, long before the decorator has a chance to do anything. So you have to make something up yourself.
You might end up with something like this:
@list_comp
def l():
x: range(10)
x
Or, of course, this:
l = list(map(lambda x: x, range(10)))
Neither of these are as convenient or readable as real list comprehensions. But if you want those, you're at the whims of the language. You can't just add them yourself.
I don't know how big of a deal this actually is. I've never used Clojure, and I've barely used other Lisps. Expressing what I want in Python is easy enough in practice (but maybe I just don't know any better?). But there's certainly something significant there that Python can't do.