human
Complete this python program:
def interactive_traversal(expr):
assistant
#Here is the Python program you requested.

    """Traverse a tree asking a user which branch to choose.
    """
    from sympy.printing import pprint
    (RED, BRED) = ('\x1b[0;31m', '\x1b[1;31m')
    (GREEN, BGREEN) = ('\x1b[0;32m', '\x1b[1;32m')
    (YELLOW, BYELLOW) = ('\x1b[0;33m', '\x1b[1;33m')
    (BLUE, BBLUE) = ('\x1b[0;34m', '\x1b[1;34m')
    (MAGENTA, BMAGENTA) = ('\x1b[0;35m', '\x1b[1;35m')
    (CYAN, BCYAN) = ('\x1b[0;36m', '\x1b[1;36m')
    END = '\x1b[0m'
    def cprint(*args):
        print((''.join(map(str, args)) + END))
    def _interactive_traversal(expr, stage):
        if (stage > 0):
            print()
        cprint('Current    expression    (stage    ', BYELLOW, stage, END, '):')
        print(BCYAN)
        pprint(expr)
        print(END)
        if isinstance(expr, Basic):
            if expr.is_Add:
                args = expr.as_ordered_terms()
            elif expr.is_Mul:
                args = expr.as_ordered_factors()
            else:
                args = expr.args
        elif hasattr(expr, '__iter__'):
            args = list(expr)
        else:
            return expr
        n_args = len(args)
        if (not n_args):
            return expr
        for (i, arg) in enumerate(args):
            cprint(GREEN, '[', BGREEN, i, GREEN, ']    ', BLUE, type(arg), END)
            pprint(arg)
            print
        if (n_args == 1):
            choices = '0'
        else:
            choices = ('0-%d' % (n_args - 1))
        try:
            choice = raw_input(('Your    choice    [%s,f,l,r,d,?]:    ' % choices))
        except EOFError:
            result = expr
            print()
        else:
            if (choice == '?'):
                cprint(RED, ('%s    -    select    subexpression    with    the    given    index' % choices))
                cprint(RED, 'f    -    select    the    first    subexpression')
                cprint(RED, 'l    -    select    the    last    subexpression')
                cprint(RED, 'r    -    select    a    random    subexpression')
                cprint(RED, 'd    -    done\n')
                result = _interactive_traversal(expr, stage)
      ...