1.3. Python基础

1.3.1. 数据类型

整型
浮点
字符串
布尔
空值

1.3.2. 变量

常量
变量

1.3.3. 字符编码

anscii: 8位作为一1B来表示一个字母
unicode: 所有语言都编码进来。
utf-8: 可变长编码, 字母使用1B存储，汉字通常是3个位

python3 中，字符串使用的是unicode编码的，是支持所有语言的。

1.3.4. 转化

In [1]: '中文'.encode("utf-8")
Out[1]: b'\xe4\xb8\xad\xe6\x96\x87'
In [3]: b'\xe4\xb8\xad\xe6\x96\x87'.decode("utf-8")
Out[3]: '中文'

1.3.5. len函数

对于str类型来说len计算的是字符数，对于bytes类型来说len计算的是bytes数。

1.3.6. 强制编码

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

1.3.7. 字符串格式化

   In [4]: print('%2d-%02d' % (3, 1))
3-01

In [5]:  'Hello, {0}, 成绩提升了 {1:.1f}%'.format('小明', 17.125)
Out[5]: 'Hello, 小明, 成绩提升了 17.1%'

In [10]: print(f'show  {b} is {a:.2f}')
show  abc is 1.00

1.3.8. list

In [12]: students=["zhao","qian","sun","li"]

In [13]: students
Out[13]: ['zhao', 'qian', 'sun', 'li']

In [14]: students.append("zhou")

In [15]: students
Out[15]: ['zhao', 'qian', 'sun', 'li', 'zhou']

In [16]: students.pop()
Out[16]: 'zhou'

In [17]: students
Out[17]: ['zhao', 'qian', 'sun', 'li']

In [18]: students[-1]="demo"

In [19]: students
Out[19]: ['zhao', 'qian', 'sun', 'demo']

In [21]: students
Out[21]: ['first', 'zhao', 'qian', 'sun', 'demo']

1.3.9. tuple

因为tuple不可变，所以代码更安全

In [22]: students = ("zhao","qian","sun")

In [23]: students
Out[23]: ('zhao', 'qian', 'sun')

1.3.10. if

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

age = 30 
if age>20 : 
    print("age >20")


if age<1: 
    print("婴儿")
elif age <3 : 
    print("学前")
elif age <18: 
    print("未成年")
else:
    print("成年人")

1.3.11. match

这个match类似其他语言的switch

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

age = 30 

match age :
    case x if x <1: 
        print("婴儿")
    case 10:
        print("age =10 ")
    case 20|21|22:
        print("age >=20 <=22")
    case _:
        print('not sure.')

1.3.12. 循环

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

students = ["zhao","qian","sun"]

for stduent in students: 
    print(stduent)

for i in range(1,10):
    print(i)

s=0
n=0
while n<=100:
    s+=n 
    n+=1
print(n)

1.3.13. dict

高效的查找速度，

1.3.14. set

方便去重