Python isn't really used for client side, because no major web browsers have Python built in.
However, Javascript has become more and more Python-like as it has evolved. You might want to study Python and Javascript together.
Take a look at https://developer.mozilla.org/en/New_in_JavaScript_1.7 and notice the Python-like nature of the new features. "array comprehensions" are just like Python list comprehensions; iterators and generators are straight out of Python; "destructuring assignments" are a standard Python idiom.
Javascript is kind of like Python with curly braces. It uses a very different inheritance model, but libraries are available that implement a more Python-like class system on top of the built-in system in Javascript.