python-浅拷贝&深拷贝
1、循环删除列表,为啥结果不正确?
a = [1,1,2,3,4,5]#原始下标为0,1,2,3,4,5 # 第一次循环,处理下标0,即1,满足条件,删除,结果[1,2,3,4,5],此时下标为0,1,2,3,4 # 第二次循环,处理下标1,即2,不满足 # 第三次循环,处理下标2,即3,满足条件,删除,结果[1,2,4,5],此时下标为 0,1,2,3 # 第四次循环,处理下标3,即5,满足条件,删除,结果[1,2,4] # 结果:[1,2,4],不符合预期,为啥还有一个1??见执行过程 for i in a: if i % 2 != 0: a.remove(i) #print(a) print(a) # 循环删list会导致下标错乱
解决方案:
a = [1,1,2,3,4,5] # 解决方法 a2 = [1,1,2,3,4,5] for i in a2: if i % 2 != 0: a.remove(i) #print(a) print(a) # 结果[[2, 4]]
2、浅拷贝&深拷贝
- 浅拷贝:dict.copy()也是浅拷贝
a = [1,1,2,3,4,5] a2 = a # 内存地址一样,肯定是浅拷贝 print(‘a‘,id(a)) print(‘a2‘,id(a2)) a3 = a.copy() # 浅拷贝:list自带的copy方法,内部地址不一样,不一定是深拷贝 print(‘a‘,id(a)) print(‘a3‘,id(a3)) a5 = copy.copy(a) # 浅拷贝 print(‘a‘,id(a)) print(‘a5‘,id(a5)) a4 = copy.deepcopy(a) # 深拷贝,只有这一种拷贝方式是深拷贝 print(‘a‘,id(a)) print(‘a4‘,id(a4))
3、实例??
class User: def __init__(self,id,status): self.id = id self.status = status users = [] u_fail_count = 0 for i in range(20): u = User(i,random.choice([‘fail‘,‘success‘])) if u.status == ‘fail‘: u_fail_count += 1 users.append(u) print(‘失败的个数‘,u_fail_count) print(‘成功的个数‘,20 - u_fail_count) def delete_item(items): # items2 = items # 浅拷贝 items2 = copy.deepcopy(items) # 深拷贝 for item in items2: if item.status == ‘fail‘: items.remove(item) # ???ValueError: list.remove(x): x not in list return items result = delete_item(users) print(len(result))
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