In [111]: tup = ([],)
In [112]: tup[0] += [1]
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-112-d4f292cf35de> in <module>()
----> 1 tup[0] += [1]
TypeError: 'tuple' object does not support item assignment
In [113]: tup
Out[113]: ([1],) # 我靠 又是亮瞎我眼睛,明明抛了异常 还能修改?
In [114]: tup = ([],)
In [115]: tup[0].extend([1])
In [116]: tup[0]
Out[116]: [1] # 好吧,我有点看明白了, 虽然我不能直接操作元组，但是不能阻止我操作元组中可变的子对象(list)
这里有个不错的解释Python's += Is Weird, Part II :
In [117]: my_tup = (1,)
In [118]: my_tup += (4,)
In [119]: my_tup = my_tup + (5,)
In [120]: my_tup
Out[120]: (1, 4, 5) # ? 嗯 不是不能操作元组嘛?
In [121]: my_tup = (1,)
In [122]: print(id(my_tup))
4481317904
In [123]: my_tup += (4,)
In [124]: print(id(my_tup))
4480606864 # 操作的不是原来的元组 所以可以
In [125]: my_tup = my_tup + (5,)
In [126]: print(id(my_tup))
4474234912
十六、python没有私有方法/变量? 但是可以有”伪”的
In [127]: class my_class(object^E):
.....: def public_method(self):
.....: print('Hello public world!')
.....: def __private_method(self): # 私有以双下划线开头
.....: print('Hello private world!')
.....: def call_private_method_in_class(self):
.....: self.__private_method()
In [132]: my_instance = my_class()
In [133]: my_instance.public_method()
Hello public world! # 普通方法
In [134]: my_instance._my_class__private_method()
Hello private world! # 私有的可以加"_ + 类名字 + 私有方法名字”
In [135]: my_instance.call_private_method_in_class()
Hello private world! # 还可以通过类提供的公有接口内部访问
In [136]: my_instance._my_class__private_variable
Out[136]: 1
十七、异常处理加else
In [150]: try:
.....: print('third element:', a_list[2])
.....: except IndexError:
.....: print('raised IndexError')
.....: else:
.....: print('no error in try-block') # 只有在try里面没有异常的时候才会执行else里面的表达式
.....:
