You can actually run a Python interpreter directly in JS thanks to emscripten.

The project is called empythoned:

Empythoned is a build script that uses Emscripten to compile CPython for use in a browser. It attempts to compile the main interpreter as a single small executable and the whole standard library as dynamically loaded libraries.

but be warned:

The project is in its infancy. Right now the core interpreter works very well, but many of the libraries either don't work at all or contain various bugs.

You can translate JavaScript to Python using Js2Py. It supports whole JavaScript and you can use it to translate large JavaScript modules like esprima.js (a JavaScript 6 parser).

>>> import js2py
>>> f = js2py.eval_js( "function $(a) {return a + arguments[1]}" )
>>> f
function $(a) { [python code] }
>>> f(1, 2, 3)
3

This is how the translated function looks like internally (it's rather ugly):

>>> print js2py.translate_js( "function $(a) {return a + arguments[1]}" )
from js2py.pyjs import *
var = Scope( JS_BUILTINS )
set_global_object(var)
# Code follows:
var.registers([u'$'])
@Js
def PyJsHoistedNonPyName(a, this, arguments, var=var):
    var = Scope({u'a':a, u'this':this, u'arguments':arguments}, var)
    var.registers([u'a'])
    return (var.get(u'a')+var.get(u'arguments').get(u'1'))
PyJsHoistedNonPyName.func_name = u'$'
var.put(u'$', PyJsHoistedNonPyName)