# 原始列表
nums = [5, 12, 7, 9, 21, 7, 14]
# 统计数字7出现的次数
count_seven = nums.count(7)
print("数字7出现的次数:",count_seven )
# 判断99是否存在,不存在则添加
if 99 not in nums:
nums.append(99)
print("添加99后的列表:",nums )
# 删除第一次出现的数字7
nums.remove(7) # 只删除第一个7
print("删除第一个7后的列表:", nums)
# 取出第2个到第4个元素(索引1到3)
sub_list = nums[1:4 ]
print("第2~4个元素组成的列表:", sub_list )
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
数字7出现的次数: 2
添加99后的列表: [5, 12, 7, 9, 21, 7, 14, 99]
删除第一个7后的列表: [5, 12, 9, 21, 7, 14, 99]
第2~4个元素组成的列表: [12, 9, 21]