Python之列表的增删改查

列表的查

a=["klvchen","tom","jack","james","lily","lucy"]
print(a[1:4])

结果：

['tom','jack','james']

注意：

列表的切片的下标以 0 为开始。即： 下标0 --> klvchen，下标1 --> tom，..... 下标5 --> lucy。

列表的切换顾头不顾尾，例如：a [1:4]，则不会取到列表下标为4的元素

从左到右，取到最后：

a=["klvchen","tom","jack","james","lily","lucy"]
print(a[1:])

结果:

['tom','jack','james','lily','lucy']

从左到右，取到倒数第二个值：

a=["klvchen","tom","jack","james","lily","lucy"]
print(a[1:-1])

结果：

['tom','jack','james','lily']

从左到右，隔一个去取：

a=["klvchen","tom","jack","james","lily","lucy"]
print(a[1::2])

结果：

['tom','james','lucy']

从右到左，一个一个去取：

a=["klvchen","tom","jack","james","lily","lucy"]
print(a[3::-1])

结果：

['james','jack','tom','klvchen']

从右到左去取

a=["klvchen","tom","jack","james","lily","lucy"]
print(a[-2:-4:-1])

结果：

['lily','james']

列表的增

append 方法默认插到最后一个位置

a=["klvchen","tom","jack","james","lily","lucy"]
a.append("mary")
print(a)

结果：

['klvchen','tom','jack','james','lily','lucy','mary']

insert 方法将数据插入到任意一个位置

a=["klvchen","tom","jack","james","lily","lucy"]
a.insert(1,"mary")
print(a)

结果：

['klvchen','mary','tom','jack','james','lily','lucy']

extend 方法可在列表的末尾一次性追加另一个序列中的多个值

a=["klvchen","tom","jack"]
b=["james","lily","lucy"]
a.extend(b)
print(a)

结果：

['klvchen','tom','jack','james','lily','lucy']

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列表的改

a=["klvchen","tom","jack","james","lily","lucy"]
a[1]="tom2"
print(a)

结果：

['klvchen','tom2','jack','james','lily','lucy']
a=["klvchen","tom","jack","james","lily","lucy"]
a[1:3]=["tom2","jack2"]
print(a)

结果：

['klvchen','tom2','jack2','james','lily','lucy']

列表的删

remove 方法

a=["klvchen","tom","jack","james","lily","lucy"]
a.remove("tom")
print(a)

结果：

['klvchen','jack','james','lily','lucy']

pop 方法

a=["klvchen","tom","jack","james","lily","lucy"]
b=a.pop(1)
print(a)
print(b)

结果：

['klvchen','jack','james','lily','lucy']
tom

注意 pop 方法会返回删除的元素

del 方法

a=["klvchen","tom","jack","james","lily","lucy"]
dela[1]
print(a)

结果：

['klvchen','jack','james','lily','lucy']
a=["klvchen","tom","jack","james","lily","lucy"]
dela
print(a)

结果：

NameError:name'a'isnotdefined

注意：del a 把列表a从内存删除了，所以打印 a 列表程序会报错

列表元素的统计

list=['a','a','b','c']
res=list.count('a')
print(res)

结果：

2

列表的排序

sort 方法

a=["klvchen","tom","jack","james","lily","lucy"]
print(a)
a.sort()
print(a)

结果：

['klvchen','tom','jack','james','lily','lucy']
['jack','james','klvchen','lily','lucy','tom']

reverse 方法

a=["klvchen","tom","jack","james","lily","lucy"]
print(a)
a.reverse()
print(a)

结果：

['klvchen','tom','jack','james','lily','lucy']
['lucy','lily','james','jack','tom','klvchen']