Python基础2 列表、字典、集合

1、列表

#1.1 切片

names = ["zhangsan","lisi","wangwu","zhuqi"]

print(names[0],names[2]) #取第1个和第3个
print(names[0:3])   # 切片 取前三个
print(names[:3])    # 切片 取前三个

print(names[-1])    #取最后一个
print(names[-3:-1]) #切片 取倒数第3和倒数第2个
print(names[-3:])   #切片 取倒数1,2,3

print(names[0:-1:2])   #切片 步长为2

#1.2插入

names = ["zhangsan","lisi","wangwu","zhuqi"]

names.append("新加入成员")       #追加到最后
names.insert(2,"insert插入")    #插入到2这个位置其他后移

#1.3修改

names = ["zhangsan","lisi","wangwu","zhuqi"]

names[1] = "bobo"  #将第二个成员改为bobo

#1.4删除

names = ["zhangsan","lisi","wangwu","zhuqi","wangba"]

del names[1]            #删除下标为1的成员
names.remove("wangwu")  #删除指定成员,无返回
names.pop()             #删除最后一个,返回删除成员
names.pop(1)            #删除下标为1的成员


print(names)

#1.5 获取元素位置

names = ["zhangsan","lisi","wangwu","zhuqi","wangba"]

names.index("lisi") #返回1

#1.6 扩展
>>> names = ["zhangsan","lisi","wangwu","zhuqi","wangba"]
>>> names2 = [1,2,3]
>>> names.extend(names2)
>>> names
['zhangsan', 'lisi', 'wangwu', 'zhuqi', 'wangba', 1, 2, 3]

#1.7 排序
>>> names = ["zhangsan","lisi","wangwu","zhuqi","wangba"]
>>> names2 = [3,5,4,2,1]
>>> names.sort(reverse=True)   #降序
>>> names2.sort()              #升序，默认reverse=False    
>>> names
['zhuqi', 'zhangsan', 'wangwu', 'wangba', 'lisi']
>>> names2
[1, 2, 3, 4, 5]

#1.8 copy 浅copy和深copy
>>> names = ["zhangsan","lisi","wangwu",[1,2,3],"zhuqi"]
>>> names2 = names.copy()  #等同names2=names[:] 或 names2 = copy.copy(names)或 names2 = list(names) 浅copy
>>> names
['zhangsan', 'lisi', 'wangwu', [1, 2, 3], 'zhuqi']
>>> names2
['zhangsan', 'lisi', 'wangwu', [1, 2, 3], 'zhuqi']
>>> names[2]="香蕉"
>>> names[3][0]="苹果"
>>> names
['zhangsan', 'lisi', '香蕉', ['苹果', 2, 3], 'zhuqi']
>>> names2
['zhangsan', 'lisi', 'wangwu', ['苹果', 2, 3], 'zhuqi']

#深copy 完全独立
import copy
names = ["zhangsan","lisi","wangwu",[1,2,3],"zhuqi","wangba"]
names2 = copy.deepcopy(names)
print(names)
print(names2)
names[2]="香蕉"
names[3][0] = "苹果"
print(names)
print(names2)

#1.9 count函数
>>> names = ["zhangsan","lisi","lisi"]
>>> names.count("lisi")
2

2、元组

一旦创建，便不能再修改，可以理解成只读列表

>>> names = ("zhangsan","lisi","wangwu")
>>> names[0]
'zhangsan'
>>> names.index("lisi")
1
>>> names.count("wangwu")
1
>>>

它只有2个方法，一个是count,一个是index

3、字典

字典一种key:value 的数据类型

语法：

>>> dict={"s1":"zhangsan","s2":"lisi","s3":"wangwu"} #创建
>>> dict
{'s1': 'zhangsan', 's2': 'lisi', 's3': 'wangwu'}
>>> dict["s2"]                                     #查看
'lisi'
>>>s2 in dict
>>>True
>>>dict.get("s2")
>>>"lisi"
>>> dict["s2"]="wangba"                            #修改
>>> dict
{'s1': 'zhangsan', 's2': 'wangba', 's3': 'wangwu'}
>>> dict["s4"]="new_s"                            #增加
>>> dict
{'s1': 'zhangsan', 's2': 'wangba', 's3': 'wangwu', 's4': 'new_s'}
>>> del dict["s1"]                                #删除
>>> dict
{'s2': 'wangba', 's3': 'wangwu', 's4': 'new_s'}
>>> dict.pop("s2")                             #删除
'wangba'
>>> dict
{'s3': 'wangwu', 's4': 'new_s'}

字典循环

info = {
    's1': "zhangsan",
    's2': "lisi",
    's3': "wangwu",
}
for key in info:                   #建议
    print(key,info[key])

for k,v in info.items():        #不建议，效率低
    print(k,v)