请问如何解决这个attribute error？

Question

如题。就是照着教材上的代码敲的，实在是看不出来哪里不对，救救孩子::>_<::

from pythonds.basic.stack import Stack # As previously defined

r_stack = Stack()

def to_str(n, base):

    convert_string = "0123456789ABCDEF"

    while n > 0:

        if n < base:

            r_stack.push(convert_string[n])

        else:

            r_stack.push(convert_string[n % base])

        n = n // base

    res = ""

    while not r_stack.is_empty():

        res = res + str(r_stack.pop())

    return res

print(to_str(1489, 16))

 

AttributeError                            Traceback (most recent call last)

<ipython-input-17-00efae08601c> in <module>

     13         res = res + str(r_stack.pop())

     14     return res

---> 15 print(to_str(1453, 16))

 

<ipython-input-17-00efae08601c> in to_str(n, base)

     10         n = n // base

     11     res = ""

---> 12     while not r_stack.is_empty():

     13         res = res + str(r_stack.pop())

     14     return res

 

AttributeError: 'Stack' object has no attribute 'is_empty'

Answer 1

Stack类的代码附出来