python基礎_1

列表，元組，集合，字典
列表——[] 可讀可寫，可以對列裏元素修改
元組——() 只讀，不可以對列裏元素修改

1.列表

in:

#列表
students = ["jack","robin","lina",3]
print (students[-2])#這兒索引爲負數-2，表示倒數第二個元素

out:

lina

in:

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

out:

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

in:

len(students)#求列表長度

out:

4

in:

students[1:3]#按區間(切片)查找元素

out:

['robin', 'lina']

in:

students = ["jack1","jack2","robin1","robin2","lina1","lina2",3]
students[1:5:2]#按區間(切片)查找元素,並設定步長爲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)#刪除元素——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=students
l

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2.元組

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個功能: 1.進行集合操作 2.消除重複元素 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 & b
print('x=',x)
#並集
y = a|b
print('y=',y)
#差集
z = a - b
print('z=',z)
#去除重複元素
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']

---

4.字典

python中字典也叫關聯數組，用{}括起來。每個元素是一個k-v對

in:

#字典
zidian = {"name":"robin","home":"yunnan"}
print(zidian["home"])

#添加字典裏的項目
zidian["like"] = "music"
print(zidian["name"])
print (zidian["like"])

out:

yunnan
robin
music

in:

zidian

out:

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

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5.常用python關鍵字

in:

#常用python關鍵字
#查看一下有哪些關鍵字
import keyword
print(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運算符與表達式

算術運算符
in:

#"*":兩個數相乘或字符串重複
a = 4 * 7
print (a)

b = "hello "*3
print (b)

out:

28
hello hello hello 

in:

#"**":求冪運算
a2 = 2 ** 3  #相當於2的三次方(冪)，就是2*2*2
print (a2)

out:

8

in:

#"//":除法運算，返回其商的整數部分，舍掉餘數
a3 = 11 // 3  
print (a3)
a4 = 11.0 // 3  
print (a4)

out:

3
3.0

in:

#"%":除法運算，返回其商的餘數部分，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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