第六章：Python高级编程-对象引用、可变性和垃圾回收
Python3高级核心技术97讲 笔记
6.1 Python中的变量是什么
#python和java中的变量本质不一样，python的变量实质上是一个指针 int str， 便利贴
a = 1
a = "abc"
#1. a贴在1上面
#2. 先生成对象 然后贴便利贴
a = [1,2,3]
b = a
print (id(a), id(b))
print (a is b)
# b.append(4)
# print (a)
6.2 ==和is的区别
a = [1,2,3,4]
b = [1,2,3,4]
print(a is b)
print(a == b)
# 对于比较小的Python不会重新创建
a = 1
b = 1
print(id(a), id(b))
print(a == b)
print(a is b)
class People:
pass
person = People() # 类是全局唯一的
if type(person) is People:
print ("yes")
6.3 del语句与垃圾回收
#cpython中垃圾回收的算法是采用 引用计数
a = object()
b = a
del a
print(b) # 有结果
print(a) # 报错
class A:
def __del__(self): # del是Python会执行这个函数的逻辑
pass
6.4 一个经典的参数错误
def add(a, b):
a += b
return a
class Company:
def __init__(self, name, staffs=[]):
self.name = name
self.staffs = staffs
def add(self, staff_name):
self.staffs.append(staff_name)
def remove(self, staff_name):
self.staffs.remove(staff_name)
if __name__ == "__main__":
com1 = Company("com1", ["bobby1", "bobby2"])
com1.add("bobby3")
com1.remove("bobby1")
print (com1.staffs)
com2 = Company("com2")
com2.add("bobby")
print(com2.staffs)
print (Company.__init__.__defaults__) # 查看默认值
com3 = Company("com3")
com3.add("bobby5")
print (com2.staffs)
print (com3.staffs)
print (com2.staffs is com3.staffs) # 没有传入，使用默认的值，所以共用了
# a = 1
# b = 2
#
# a = [1,2] # a是可变的哦
# b = [3,4]
#
# a = (1, 2)
# b = (3, 4)
#
# c = add(a, b)
#
# print(c)
# print(a, b)