# 删除 li = [11, 22, 33, 44, 'rock']中索引为单数的元素

# 方法一

del li[1::2]

print(li)   # [11, 33, 'rock']

# 方法二

new_li = []

for index in range(len(li)):

    print(index)

    if index % 2 == 0:

        new_li.append(li[index])

li = new_li

print(li)

# 方法三

# 取首不取尾

for index in range(len(li)-1, 0-1, -1):

    print(index)

    if index % 2 != 0:

        li.pop(index)

print(li)

# 错误示例

for index in range(len(li)):

    print(index)

    if index % 2 != 0:

        li.pop(index)

print(li)

# 删除 dic = {'k1': 1, 'k2': 1, 'k3': 1, 'name': 'rock'}中所有包含k字母的键值对

# dict字典在循环时不能改变字典的长度，即不能增删改查字典中的元素

dic = {'k1': 1, 'k2': 1, 'k3': 1, 'name': 'rock'}

li = []

for key in dic.keys():

    if 'k' in key:

        li.append(key)

for i in li:

    dic.pop(i)

print(dic)  # {'name': 'rock'}

# 错误示例 RuntimeError: dictionary changed size during iteration

for key in dic.keys():

    if 'k' in key:

        dic.pop(key)

print(dic)

for key in dic.keys():

    print(key[0])

    if key[0] == 'k':

        dic.pop(key)

print(dic)