The basis of the contents of -2

A, while circulation

while: the condition is satisfied for an infinite loop

structure:

while 条件:
    循环结果

Examples

while True:
    print("一号")
    print("二号")
    print("三号")

How to terminate the loop

Changing conditions

#实例
flag = True
while flag:
    print(1)
    print(2)
    flag = False
    print(4)
    print(5)

break: exit loop when it encounters a break cycle

while True:
    print(1)
    print(2)
    break
    print(3)
    print(4)

#只会输出1 2 不会输出 3 4

continue: skip this cycle

a = 0
while a < 5:
    a += 1
    if a == 3:
        continue
    print(a)

Exercise 1: 0 to 100 Digital Print

num = 0
while num < 101:
    print(num)
    num += 1

Exercise 2: Print + 1 + 2 + 3 .... 100

num = 1
count = 0
while num < 101:
    count += num
    num += 1
print(count)

while else structure

while 条件:
    循环体
else:
    结果

Examples

count = 1
while count < 5:
    print(count)
    count += 1
else:
    print("结束了。。")

When the break, and will not go else

Second, formatted output

% : Placeholder

symbol	Explanation
%s	Formatted as a string
%c	Formatting characters and their ASCII code
%d	Integer format
in%	Unsigned int format
%f	Format floating point numbers, the point precision may be designated
%%	Output% (percent sign format string contains, must %%)

Example:

name = "小明"
age = 14
message = "你好，我叫 %s，年龄 %d" %(name,age)
print(message)

Note: The number in parentheses and order must be consistent

In the output format to express the percent sign, plus a percent sign in front of the percent sign

name = "小明"
age = 14
message = "你好，我叫 %s，年龄 %d,进度1%%" %(name,age)
print(message)

Third, the operator

3.1 operator class

Arithmetic operators
Logical Operators
Comparison Operators
Copy operator
Member operator
Identity operator
Bitwise Operators

Arithmetic operators 3.2

Operators	description
+	plus
-	Less
	Multiply
/	except
%	Modulo
**	power
//	Take divisible

3.3 Comparison Operators

Operators	description
==	equal
!=	not equal to
>	more than the
<	Less than
>=	greater or equal to
<=	Less than or equal

3.4 Assignment Operators

Operators	description
=	Simple assignment operator
+=	Addition assignment operators, for example: a + = 2 is equivalent to: a = a + 2
-=	Subtraction assignment operator, for example: a - = 2 is equivalent to: a = a - 2
*=	Multiplication assignment operators, for example: A = 2 is equivalent to: A = A 2
/=	Division assignment operator, for example: a / = 2 is equivalent to: a = a / 2
%=	Modulo assignment operators, for example: a% = 2 is equivalent to: a = a% 2
**=	Power assignment operators, for example: a = 2 is equivalent to: a = a 2
//=	Take divisible assignment operators, for example: a // = 2 is equivalent to: a = a // 2

3.5 Logical Operators

Operators	description
and	versus
or	or
not	non-

Priority: in the absence () of

not > and > or

The consent of the priority cases, calculated from left to right

Case 1: the operational sides are relatively
```
print(2 > 3 and 3 < 4 or 5 < 6)
```

Case 2: Both sides are integers

print(8 or 5)
print(0 or 3)

# x or y : x为真，值为x；x为假，值为y
# x and y : x为真，值为y；x为假，值为x

in and not in: determining whether an element in the string, a tuple, list or dictionary

Fourth, the coding

4.1 编码类别

ASCII：美国信息交换标准编码
国标：中华人民共和国国家标准信息交换用汉字编码
GBK：GB码的扩展字符编码
Unicode：将世界上所有字符都收入的编码
UTF-8：根据不同字符选择编码长度

4.2 ASCII

规定了一个字符用一个8位的二进制数表示（0000 0001）
最多只能表示256个字符，即 2**8=256
8bit = 1byte

ASCII编码

4.3 GBK 国标码

规定一个字符用2个8位的二进制数表示，即16位（0000 0001 0001 0011）
可以表示65535个字符，即 2**16 = 65535
兼容了ASCII，扩充了中文字符

4.4 Unicode UTF-8

号称收纳了世界所有字符的编码
扩充到了32位，也就是4个8位的二进制数
可以表示2**32个字符
由于太过浪费，提出了UTF-8，可变长度的编码
UTF-8是对Unicode编码的压缩和优化，将所有字符进行分类：ASCII编码的内容用1个字节、欧洲字符用2个字节。。。

4.5 单位转换

8bit = 1byte

1024byte = 1KB

1024KB = 1MB

1024MB = 1GB

1024GB = 1TB

1024TB = 1PB

1024PB = 1EB

1024EB = 1ZB

1024ZB = 1YB

1024YB = 1NB

1024NB = 1DB