def filter_chars():
    # This is not in style. RE is too high-level, but using it
    # for doing this fast and short. Push the pattern onto stack
    stack.append(re.compile('[\W_]+'))
    # Push the result onto the stack
    stack.append([stack.pop().sub(' ', stack.pop()[0]).lower()])
Takes data on the stack and places back a copy with all 
dataset/ETHPy150Open crista/exercises-in-programming-style/02-go-forth/tf-02.py/filter_chars