...: print("class A")
...:
In [2]: class B(object):
...: def foo(self):
...: print("class B")
...:
In [3]: class C(A, B):
...: pass
...:
In [4]: C().foo()
class A # 例子很好懂, C继承了A和B，从左到右,发现A有foo方法,返回了
看起来都是很简单, 有次序的从底向上,从前向后找,找到就返回. 再看例子:
In [5]: class A(object):
...: def foo(self):
...: print("class A")
...:
In [6]: class B(A):
...: pass
...:
In [7]: class C(A):
...: def foo(self):
...: print("class C")
...:
In [8]: class D(B,C):
...: pass
...:
In [9]: D().foo()
class C # ? 按道理, 顺序是 D->B->A,为什么找到了C哪去了
这也就涉及了MRO(Method Resolution Order):
In [10]: D.__mro__
Out[10]: (__main__.D, __main__.B, __main__.C, __main__.A, object)
简单的理解其实就是新式类是广度优先了， D->B, 但是发现C也是继承A，就先找C，最后再去找A
九、列表的+和+=, append和extend
In [17]: print('ID:', id(a_list))
('ID:', 4481323592)
In [18]: a_list += [1]
In [19]: print('ID (+=):', id(a_list))
('ID (+=):', 4481323592) # 使用+= 还是在原来的列表上操作
In [20]: a_list = a_list + [2]
In [21]: print('ID (list = list + ...):', id(a_list))
('ID (list = list + ...):', 4481293056) # 简单的+其实已经改变了原有列表
In [28]: a_list = []
In [29]: id(a_list)
Out[29]: 4481326976
In [30]: a_list.append(1)
In [31]: id(a_list)
Out[31]: 4481326976 # append 是在原有列表添加
In [32]: a_list.extend([2])
In [33]: id(a_list)
Out[33]: 4481326976 # extend 也是在原有列表上添加
十、datetime也有布尔值
这是一个坑
In [34]: import datetime
In [35]: print('"datetime.time(0,0,0)" (Midnight) ->', bool(datetime.time(0,0,0)))
('"datetime.time(0,0,0)" (Midnight) ->', False)
In [36]: print('"datetime.time(1,0,0)" (1 am) ->', bool(datetime.time(1,0,0)))
('"datetime.time(1,0,0)" (1 am) ->', True)
