It's pretty horrible, but this adds support for parentheses inside the `full_eval` function:

  from itertools import takewhile, dropwhile

  def split_paren(expr):
      left = ''.join(takewhile(lambda c: c != '(', expr))
      right = ''.join(takewhile(lambda c: c != ')', expr[::-1]))[::-1]
      inside = ''.join(dropwhile(lambda c: c != ')', ''.join(dropwhile(lambda c: c != '(', expr))[::-1]))[::-1][1:-1]
      return left, inside, right

  def full_eval(expr):
      if '(' in expr:
          left, inside, right = split_paren(expr)
          return full_eval(left + str(full_eval(inside)) + right)
      else:
          return calc(expr)