python基础

列表

列表是最常用的数据类型之一，通过列表可以对数据实现最方便的存储、修改等操作

1.定义列表

fruits = [‘apple’,’banana’,’orange’]

2.通过下标访问列表中的元素，下标从0开始计数

>>> fruits[0]
‘apple’
>>> fruits[2]
‘orange’
>>> fruits[-1]
‘orange’
>>> fruits[-2]
‘banana’

3.切片

>>> fruits = [‘apple’,’banana’,’orange’,’peal’,’grape’]
>>> fruits[1:4] #取下标1到下标4之间的数，包括1但不包括4
[‘banana’, ‘orange’, ‘peal’]
>>> fruits[1:-1] #取下标1至-1之间的数，不包括-1
[‘banana’, ‘orange’, ‘peal’]
>>> fruits[0:3] #从头开始取，不包括3
[‘apple’, ‘banana’, ‘orange’]
>>> fruits[:3] #和上句一样
[‘apple’, ‘banana’, ‘orange’]
>>> fruits[3:] #从下标3到最后，到末尾只能这样取
[‘peal’, ‘grape’]
>>> fruits[0::2] #从头开始，步长为2，即隔一个取一个
[‘apple’, ‘orange’, ‘grape’]
>>> fruits[::2] #和上句一iy
[‘apple’, ‘orange’, ‘grape’]

4.追加，append()

>>> fruits
[‘apple’, ‘banana’, ‘orange’, ‘peal’, ‘grape’]
>>> fruits.append(‘newpeach’)
>>> fruits
[‘apple’, ‘banana’, ‘orange’, ‘peal’, ‘grape’, ‘newpeach’]

5.插入元素，insert()

在下标1处插入一个西瓜(watermelon)

[‘apple’, ‘banana’, ‘orange’, ‘peal’, ‘grape’, ‘newpeach’]
>>> fruits.insert(1,’watermelon’)
>>> fruits
[‘apple’, ‘watermelon’, ‘banana’, ‘orange’, ‘peal’, ‘grape’, ‘newpeach’]

6.修改列表中的元素

将banana修改为樱桃cherry

>>> fruits
[‘apple’, ‘watermelon’, ‘banana’, ‘orange’, ‘peal’, ‘grape’, ‘newpeach’]
>>> fruits[2]=’cherry’
>>> fruits
[‘apple’, ‘watermelon’, ‘cherry’, ‘orange’, ‘peal’, ‘grape’, ‘newpeach’]

7.删除

pop()在默认删除最后一个元素后，会返回该元素

>>> fruits
[‘apple’, ‘watermelon’, ‘cherry’, ‘orange’, ‘peal’, ‘grape’, ‘newpeach’]
>>> del fruits[2] #删除第二个元素
>>> fruits
[‘apple’, ‘watermelon’, ‘orange’, ‘peal’, ‘grape’, ‘newpeach’]
>>> fruits.remove(‘orange’) #删除指定的元素
>>> fruits
[‘apple’, ‘watermelon’, ‘peal’, ‘grape’, ‘newpeach’]
>>> fruits.pop() #删除最后一个元素
‘newpeach’
>>> fruits
[‘apple’, ‘watermelon’, ‘peal’, ‘grape’]

8.扩展 extend()

>>> fruits
[‘apple’, ‘watermelon’, ‘peal’, ‘grape’]
>>> vegetable = [‘radish’,’cabbage’,’cucumber’]
>>> fruits
[‘apple’, ‘watermelon’, ‘peal’, ‘grape’]
>>> vegetable
[‘radish’, ‘cabbage’, ‘cucumber’]
>>> fruits.extend(vegetable)
>>> fruits
[‘apple’, ‘watermelon’, ‘peal’, ‘grape’, ‘radish’, ‘cabbage’, ‘cucumber’]

9.拷贝 copy()

[‘apple’, ‘watermelon’, ‘peal’, ‘grape’, ‘radish’, ‘cabbage’, ‘cucumber’]
>>> fruits2 = fruits.copy()
>>> fruits2
[‘apple’, ‘watermelon’, ‘peal’, ‘grape’, ‘radish’, ‘cabbage’, ‘cucumber’]

10.统计 count()

>>> fruits.count(‘apple’)
1

11.排序 sort() 和翻转 reverse()

>>> fruits
[‘apple’, ‘watermelon’, ‘peal’, ‘grape’, ‘radish’, ‘cabbage’, ‘cucumber’]
>>> fruits.sort()
>>> fruits
[‘apple’, ‘cabbage’, ‘cucumber’, ‘grape’, ‘peal’, ‘radish’, ‘watermelon’]
>>> fruits.reverse()
>>> fruits
[‘watermelon’, ‘radish’, ‘peal’, ‘grape’, ‘cucumber’, ‘cabbage’, ‘apple’]

12.获取下标 index()

[‘watermelon’, ‘radish’, ‘peal’, ‘grape’, ‘cucumber’, ‘cabbage’, ‘apple’]
>>> fruits.index(‘apple’)
6
# 只返回找到的第一个下标

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