Python全栈（第一期）Day7

一，基础类型汇总

1，Str

S.isspace() -> bool
Return True if all characters in S are whitespace
and there is at least one character in S, False otherwise.

s1 = ' '
s2 = ''
s3 = 'python'
print(s1.isspace())
print(s2.isspace())
print(s3.isspace())

输出结果：
True
False
False

2，List

问题：把列表中索引奇数位置删除（22,44）

lis = [11, 22, 33, 44, 55]
#第一种
lis = lis[::2]
print(lis)

#第二种
l1 = []
for i in lis:
    if lis.index(i) % 2 == 0:
        l1.append(i)
lis = l1
print(lis)

#第三种
for i in range(len(lis)-1, -1, -1):
    if i % 2 == 1:
        del lis[i]
print(lis)

输出结果：
[11, 33, 55]

3，dict

fromkeys:Returns a new dict with keys from iterable and values equal to value.

dic = dict.fromkeys([1, 2, 3], '春哥')
print(dic)
dic = dict.fromkeys([1, 2, 3], [])
print(dic)
dic[1].append('袁姐')
print(dic)
dic[2].extend('二哥')
print(dic)

输出结果：
{1: ‘春哥’, 2: ‘春哥’, 3: ‘春哥’}
{1: [], 2: [], 3: []}
{1: [‘袁姐’], 2: [‘袁姐’], 3: [‘袁姐’]}
{1: [‘袁姐’, ‘二’, ‘哥’], 2: [‘袁姐’, ‘二’, ‘哥’], 3: [‘袁姐’, ‘二’, ‘哥’]}

4，tuple

如果元祖里面只有一个元素且不加,那此元素是什么类型，就是什么类型。（面试题）

tu1 = (1)
tu2 = (1,)
print(tu1, type(tu1))
print(tu2, type(tu2))

输出结果：
1 <class ‘int’>
(1,) <class ‘tuple’>

二，集合

集合：可变的数据类型，他里面的元素必须是不可变的数据类型，无序，不重复。

1，增

set1 = {'alex', 'wusir', 'ritian', 'egon', 'barry'}
#add
set1.add('女神')
print(set1)
#update
set1.update('abc')
print(set1)

输出结果：
{‘barry’, ‘egon’, ‘wusir’, ‘女神’, ‘alex’, ‘ritian’}
{‘barry’, ‘b’, ‘egon’, ‘wusir’, ‘a’, ‘c’, ‘女神’, ‘alex’, ‘ritian’}

2，删

set1 = {'alex', 'wusir', 'ritian', 'egon', 'barry'}

set1.remove('egon')  # 按元素
print(set1)

str = set1.pop()  # 随机删除
print('随机删除：', str)  # 有返回值
print(set1)


set1.clear()
print(set1)

del set1 #删除集合

输出结果：
{‘barry’, ‘ritian’, ‘alex’, ‘wusir’}
随机删除： barry
{‘ritian’, ‘alex’, ‘wusir’}
set()

3，下面是集合最牛逼的地方

set1 = {1, 2, 3, 4, 5}              #交集
set2 = {4, 5, 6, 7, 8}
set3 = set1 & set2
print(set3)  # {4, 5}
print(set1.intersection(set2))  # {4, 5}

print('*************************************************')

set1 = {1, 2, 3, 4, 5}           #并集
set2 = {4, 5, 6, 7, 8}
print(set1 | set2)  # {1, 2, 3, 4, 5, 6, 7,8}
print(set2.union(set1))  # {1, 2, 3, 4, 5, 6, 7}

print('*************************************************')

set1 = {1, 2, 3, 4, 5}       #反交集
set2 = {4, 5, 6, 7, 8}
print(set1 ^ set2)  # {1, 2, 3, 6, 7, 8}
print(set1.symmetric_difference(set2))  # {1, 2, 3, 6, 7, 8}

print('*************************************************')

set1 = {1, 2, 3, 4, 5}       #差集
set2 = {4, 5, 6, 7, 8}
print(set1 - set2)  # {1, 2, 3}  set1独有的
print(set1.difference(set2))  # {1, 2, 3}

print('*************************************************')

set1 = {1,2,3,}                 #子集与超集
set2 = {1,2,3,4,5,6}

print(set1 < set2)
print(set1.issubset(set2))     # 这两个相同，都是说明set1是set2子集。

print(set2 > set1)
print(set2.issuperset(set1))  # 这两个相同，都是说明set2是set1超集。

输出结果：
{4, 5}
{4, 5}
Hello world
{1, 2, 3, 4, 5, 6, 7, 8}
{1, 2, 3, 4, 5, 6, 7, 8}
Hello world
{1, 2, 3, 6, 7, 8}
{1, 2, 3, 6, 7, 8}
Hello world
{1, 2, 3}
{1, 2, 3}
Hello world
True
True
True
True

4，另外补充一点小知识

#去重（面试题）
li = [1, 2, 33, 33, 2, 1, 4, 5, 6, 6]
set1 = set(li)
print(set1)
li = list(set1)
print(li)

输出结果：
{1, 2, 33, 4, 5, 6}
[1, 2, 33, 4, 5, 6]

三，了解几个赋值运算

l1 = [1, 2, 3]
l2 = l1
l1.append('a')
print(l1, l2)

输出结果：
[1, 2, 3, ‘a’] [1, 2, 3, ‘a’]

#copy
l1 = [1, 2, 3]
l2 = l1.copy()
print(l1, l2)
print(id(l1), id(l2))
l2.append('a')
print(l1, l2)

输出结果：
[1, 2, 3] [1, 2, 3]
1796823956936 1796824090056
[1, 2, 3] [1, 2, 3, ‘a’]