This syntax file displays unicode characters for some Python operators and built-in functions, turning the following:

    map (lambda x: x, [1,2,3])

    def foo(e, a):
        if e in [1,2,3] and not a:
            return math.sqrt(math.pi)
        else:
            return sum([1,2,3])

into

    map (λ x: x, [1,2,3])

    def foo(e, a):
        if e ∈ [1,2,3] ∧ ¬a:
            return √(π)
        else:
            return ∑([1,2,3])

Screenshot:

This does not – at any point – alter your source code. It simply uses Vim's "conceal" feature to “hide” in behind ∈, etc. Whenever the cursor is at a line with concealed text, the text will be expanded.

To install, simply put python.vim in ~/.vim/after/syntax or use something like Pathogen (recommended).

Vim ≥ 7.3 is required.

This plug-in is very much inspired by http://github.com/Twinside/vim-haskellConceal