Python assert断言声明,遇到错误则立即返回问题

# 等价于
if not expression:
    raise AssertionError

>>> import numpy as np
>>> w = np.zeros((5,1))
>>> w
array([[0.],
       [0.],
       [0.],
       [0.],
       [0.]])
>>> assert(w.shape == (5,1))
>>> assert(w.shape == (2,1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError

>>assert 1==1
>> assert 1 == 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError

>>assert 2+2==2*2
>>assert len(['my boy',12])<10
>>assert range(4)==[0,1,2,3]
>>> mylist = ['item']
>>assert len(mylist) >= 1
>>mylist.pop()
'item'
>>assert len(mylist) >= 1
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AssertionError

class ShortInputException(Exception):
    '''自定义的异常类'''
    def __init__(self, length, atleast):
        #super().__init__()
        self.length = length
        self.atleast = atleast

def main():
    try:
        s = input('请输入 --> ')
        if len(s) < 3:
            # raise引发一个你定义的异常
            raise ShortInputException(len(s), 3)
    except ShortInputException as result:#x这个变量被绑定到了错误的实例
        print('ShortInputException: 输入的长度是 %d,长度至少应是 %d'% (result.length, result.atleast))
    else:
        print('没有异常发生.')

main()