python基础_1

列表，元组，集合，字典
列表——[] 可读可写，可以对列里元素修改
元组——() 只读，不可以对列里元素修改

1.列表

in:

#列表students = ["jack","robin","lina",3]print (students[-2])#这儿索引为负数-2，表示倒数第二个元素

out:

lina

in:

students[3] = "python"print (students[3])print (students)

out:

python['jack', 'robin', 'lina', 'python']

in:

len(students)#求列表长度

out:

4

in:

students[1:3]#按区间(切片)查找元素

out:

['robin', 'lina']

in:

students = ["jack1","jack2","robin1","robin2","lina1","lina2",3]students[1:5:2]#按区间(切片)查找元素,并设定步长为2

out:

['jack2', 'robin2']

in:

students.append('helloworld')#添加元素students

out:

['jack1', 'jack2', 'robin1', 'robin2', 'lina1', 'lina2', 3, 'helloworld']

in:

students.pop(7)#删除元素——按索引students

out:

['jack1', 'jack2', 'robin1', 'robin2', 'lina1', 'lina2', 3]

in:

students.insert(1,'helloworld2')#插入元素——按索引students

out:

['jack1', 'helloworld2', 'jack2', 'robin1', 'robin2', 'lina1', 'lina2', 3]

in:

scores = [10,20,30]students.insert(1,scores)students

out:

['jack1', [10, 20, 30], [10, 20, 30], [10, 20, 30], [10, 20, 30], [10, 20, 30], [10, 20, 30], [10, 20, 30], 'helloworld2', 'jack2', 'robin1', 'robin2', 'lina1', 'lina2', 3]

in:

l=studentsl

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2.元组

in:

students = ("jack1","jack2","robin1","robin2","lina1","lina2",3)print(students[2])

out:

robin1

in:

students.append(score)#添加元素students

in:

teachers = ("jack1","jack2","robin1","robin2","lina1","lina2",scores)teachers

out:

('jack1', 'jack2', 'robin1', 'robin2', 'lina1', 'lina2', [10, 20, 30])

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3.集合

主要有2个功能: 1.进行集合操作 2.消除重复元素 集合的格式是:set(元素)
in:

a = set("abcnmaaaaggsng")print('a=',a)b = set("cdfm")print('b=',b)#交集x = a & bprint('x=',x)#并集y = a|bprint('y=',y)#差集z = a - bprint('z=',z)#去除重复元素new = set(a)print('z=',z)

out:

a= {'g', 'b', 'm', 's', 'a', 'c', 'n'}b= {'d', 'm', 'f', 'c'}x= {'m', 'c'}y= {'g', 'b', 'm', 'd', 's', 'f', 'a', 'c', 'n'}z= {'g', 'b', 'n', 's', 'a'}z= {'g', 'b', 'n', 's', 'a'}

in:

strs = 'abc'strs[1]

out:

'b'

in:

L = {'a','b','c','c'}L

out:

{'a', 'b', 'c'}

in:

set_L = set(L)list_L = list(set_L)list_L

out:

['b', 'a', 'c']

in:

tuple_L = tuple(set_L)tuple_L

out:

('b', 'a', 'c')

in:

list(tuple_L)

out:

['b', 'a', 'c']

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4.字典

python中字典也叫关联数组，用{}括起来。每个元素是一个k-v对

in:

#字典zidian = {"name":"robin","home":"yunnan"}print(zidian["home"])#添加字典里的项目zidian["like"] = "music"print(zidian["name"])print (zidian["like"])

out:

yunnanrobinmusic

in:

zidian

out:

{'home': 'yunnan', 'like': 'music', 'name': 'robin'}

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5.常用python关键字

in:

#常用python关键字#查看一下有哪些关键字import keywordprint(keyword.kwlist)

out:

['False', 'None', 'True', 'and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']

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6.python运算符与表达式

算术运算符
in:

#"*":两个数相乘或字符串重复a = 4 * 7print (a)b = "hello "*3print (b)

out:

28hello hello hello 

in:

#"**":求幂运算a2 = 2 ** 3  #相当于2的三次方(幂)，就是2*2*2print (a2)

out:

8

in:

#"//":除法运算，返回其商的整数部分，舍掉余数a3 = 11 // 3  print (a3)a4 = 11.0 // 3  print (a4)

out:

33.0

in:

#"%":除法运算，返回其商的余数部分，舍掉商a5 = 11 % 3  print (a5)

out:

2

range
in:

range(0,10,2)alist = range(10)[x*x for x in alist]

out:

[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

in:

[x*x for x in alist if x%3]

out:

[1, 4, 16, 25, 49, 64]

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截图