python基础之列表篇

LIST:

简介：列表是python中最基本的数据结构之一，每个元素都会被分配一个数字也就是索引，亦称为下标。他的第一个元素对应的索引为0，第二个对应的索引为1,以此类推。

一, 列表的声明与赋值

#列表的声明
list1 = ['pisa','heitang','lurou','mianhuatang']
list2 = ['cat','dog','pig']
list3 = ['softdrink','wine','bear']

二，列表的查询

'''
如何读取列表中的元素？
'''
list1 = ['pisa','heitang','mianhuatang']

cat1 = list1[0] #pisa
cat2 = list1[1] #heitang
cat3 = list[2] # mianhuatang
cat4 = list[-1] # mianhuatang
cat5 = list[-2] #heitang
cat6 = list[-3] # pisa

三，列表的切片

'''
列表的切片
'''
list = ['pisa','heitang','mianhuatang','lurou','panghua']
#获取前三只猫
getThreeCat = list[:3] 
getThreeCat = list[0:3]
#获取第二只猫和第四只猫 heitang,lurou
getSecondAndFourthCat = list[1:4:2] #['heitang','lurou']
getSecondAndFourthCat = list[-4:-1:2]
#获取最后一只猫 panghua
getLastCat = list[-1]
#让整个吃货家族反转
getReverseCat = list[::-1]#['panghua', 'lurou', 'mianhuatang', 'heitang', 'pisa']

 四，列表添加元素

'''
列表添加元素的三种方法 insert(插入) extend(迭代添加) append(追加)
'''
#列表的添加之 append
list1 = ['pisa','lurou']
list1.append('mianhuatang') #['pisa','lurou','mianhuatang']

#列表的迭代添加
list1 = ['pisa','mianhuatang','lurou']
list2 = ['heitang','panghua']
list1.extend(list2) # ['pisa', 'mianhuatang', 'lurou', 'heitang', 'panghua']
list2.extend(list1) # ['heitang', 'panghua', 'pisa', 'mianhuatang', 'lurou']

#指定位置添加insert(索引,元素) 
list1 = ['heitang','pisa','lurou']
list1.insert(1,'panghua') # ['heitang', 'panghua', 'pisa', 'lurou']

五，列表删除元素

'''
列表删除元素 pop,del,remove,clear以及切片的舍弃
'''
#pop() 默认删除最后一个元素，并返回，如果指定索引，则删除对应的值，后面元素的索引自动减一

list = ['pisa','mianhuatang','heitang','lurou','panghua']
cat1 = list.pop() #panghua
print(list) #['pisa','panghua','heitang','lurou']

list2 = ['pisa','mianhuatang','heitang','lurou','panghua']
cat2  = list2.pop(2) # heitang
print(list2) #['pisa','mianhuatang','lurou','panghua']

#del 是删除整个列表，也就是从内存中抹去这个列表的指针
list3 = ['pisa','mianhuatang','heitang','lurou','panghua']
print(list3) #['pisa','mianhuatang,'heitang','lurou','panghua']
del list3
print(list3) # NameError: name 'list3' is not defined

#remove() 是 删除元素，一次也只能删除一个元素,返回值 None
list4 = ['pisa','mianhuatang','heitang','lurou','panghua']
list4.remove('pisa')  #['mianhuatang', 'heitang', 'lurou', 'panghua']

#clear 清空整个列表
list5 = ['pisa','mianhuatang','heitang','lurou','panghua']
list5.clear() # []

#切片删除相应的元素
list6 =  ['pisa','mianhuatang','heitang','lurou','panghua']
list7 = list6[0:2] #  得到['pisa','mianhuatang'] 删除了heitang,lurou和panghua

六，列表的更新

#重新赋值法
list1 = ['a','b','c','d']
list1[1] = 3;#['a',3,'c','d']
#可迭代对象
list2 = ['a','b','c','d']
list2[:2] = '89' #[8,9,'c','d']
list3 = ['a','b','c','d']
list3[:3] = '56' #['5','6','d'] ?为什么是['5','6','d']而不是['5','6','5','d']或者['5','6','c','d']? 首先迭代对象只能循环一次，也是'5'和'6',而切片只是要覆盖'a','b','c',而我们迭代对象只有两位，这样就少了一位，就舍弃掉，变成了['5','6','d']

七，列表的内置函数

#列表的长度
list1 = ['pisa','mianhuatang','panghua','lurou','heitang']
cat_len = len(list1) # 5

#列表的copy 复制一个副本给其他变量
list2 = ['pisa','mianhuatang','panghua','lurou','heitang']
list3 = list2.copy()
print(list3) # ['pisa','mianhuatang','panghua','lurou','heitang'] 需要特别的注意python2.x 没有copy方法

#列表的count 统计出现的次数 返回一个Integer
list4 = ['a','b','c','c','d']
list4.count('c') # 2

#列表的index 查询L.index(value, [start, [stop]]) 如果没有则报错(ValueError)
list5 = ['pisa','mianhuatang','panghua','lurou','heitang']
list5.index('panghua') # 2
list5.index('heierduo') # ValueError

#sort    L.sort(key=None, reverse=False) 没有返回值
list6 = [1,3,5,3,7,0]
list6.sort() # [0, 1, 3, 3, 5, 7]
list6.sort(reverse=True) # [7, 5, 3, 3, 1, 0]

#reverse 反转 L.reverse() -- reverse *IN PLACE*
list7 =  ['a','b','c','d']
list7.reverse() # ['d', 'c', 'b', 'a']

# append,clear,extend,insert,pop,remove,上面已经提及过

列表的循环遍历
1.for循环
    nameList = ['zhangsan','lisi','wangwu']
    for i in nameList:
        print(i)
    
    结果：
        zhangsan
        lisi
        wangwu

    for i in nameList:
        print(nameList.index(i))
    
    结果：
        0
        1
        2

2.while循环
    nameList = ['zhangsan','lisi','wangwu']
    len1 = len(nameList)
    while len1>=0:
        print(nameList[len1])
        len1 -=1
    结果：
        wangwu
        lisi
        zhangsan