1. 变量类型

• 在Python中，变量不需要明确的声明类型来保留内存空间。当向变量分配值时，Python会自动发出声明。

counter = 100          # 一个整型数
miles   = 999.99       # 一个浮点数
name    = "Maxsu"       # 一个字符串
site_url  = "http://www.yiibai.com" # 一个字符串

print (counter)
print (miles)
print (name)
print (site_url)

五种标准数据类型

2. 数字

• 支持int(有符号整数) float(浮点实值) complex(复数)

//创建数字对象
var1 = 10
var2 = 20
//删除一个或者多个
del var1, var2

3. 字符串

• 可以使用片段运算符([]和[:])来获取字符串的子集(子字符串)，其索引从字符串开始处的索引0开始，并且以-1表示字符串中的最后一个字符。
• 三重引号允许字符串跨越多行，包括逐字记录的新一行

str = 'yiibai.com'

print ('str = ', str)          # Prints complete string
print ('str[0] = ',str[0])       # Prints first character of the string
print ('str[2:5] = ',str[2:5])     # Prints characters starting from 3rd to 5th
print ('str[2:] = ',str[2:])      # Prints string starting from 3rd character
print ('str[-1] = ',str[-1])      # 最后一个字符，结果为：'!'
print ('str * 2 = ',str * 2)      # Prints string two times
print ('str + "TEST" = ',str + "TEST") # Prints concatenated string

4. 数组

• 存储在列表中的值可以使用切片运算符([]和[:])来访问，索引从列表开头的0开始，并且以-1表示列表中的最后一个项目。 加号(+)是列表连接运算符，星号(*)是重复运算符。

list = [ 'yes', 'no', 786 , 2.23, 'minsu', 70.2 ]
tinylist = [100, 'maxsu']

print ('list = ', list)          # Prints complete list
print ('list[0] = ',list[0])       # Prints first element of the list
print ('list[1:3] = ',list[1:3])     # Prints elements starting from 2nd till 3rd 
print ('list[2:] = ',list[2:])      # Prints elements starting from 3rd element
print ('list[-3:-1] = ',list[-3:-1])    
print ('tinylist * 2 = ',tinylist * 2)  # Prints list two times
print ('list + tinylist = ', list + tinylist) # Prints concatenated lists

5. 元组

 - 列表和元组之间的主要区别是 - 列表括在括号(`[]`)中，列表中的元素和大小可以更改，而元组括在括号(`()`)中，`无法更新`。元组可以被认为是`只读`列表。

tuple = ( 'maxsu', 786 , 2.23, 'yiibai', 70.2  )
tinytuple = (999.0, 'maxsu')

# tuple[1] = 'new item value' 不能这样赋值

print ('tuple = ', tuple)           # Prints complete tuple
print ('tuple[0] = ', tuple[0])        # Prints first element of the tuple
print ('tuple[1:3] = ', tuple[1:3])      # Prints elements starting from 2nd till 3rd 
print ('tuple[-3:-1] = ', tuple[-3:-1])       # 输出结果是什么？
print ('tuple[2:] = ', tuple[2:])       # Prints elements starting from 3rd element
print ('tinytuple * 2 = ',tinytuple * 2)   # Prints tuple two times
print ('tuple + tinytuple = ', tuple + tinytuple) # Prints concatenated tuple

6. 字典

• 字典由大括号({})括起来，可以使用方括号([])分配和访问值。
• 字典中的元素没有顺序的概念。是根据哈希算法来分配位置的

dict = {}
dict['one'] = "This is one"
dict[2]     = "This is my"

tinydict = {'name': 'maxsu', 'code' : 1024, 'dept':'IT Dev'}


print ("dict['one'] = ", dict['one'])       # Prints value for 'one' key
print ('dict[2] = ', dict[2])           # Prints value for 2 key
print ('tinydict = ', tinydict)          # Prints complete dictionary
print ('tinydict.keys() = ', tinydict.keys())   # Prints all the keys
print ('tinydict.values() = ', tinydict.values()) # Prints all the values

7. 类型转换

8. 特殊运算符

9. 函数

def changeme( mylist ):
    //形参: 内部变量,修改不影响外部变量
    mylist = [1,2,3,4] # This would assi new reference in mylist
    print ("Values inside the function: ", mylist)
    return

//外部变量
mylist = [10,20,30]
changeme( mylist )
print ("Values outside the function: ", mylist)

默认参数

def printinfo( name, age = 25 ):
   "This prints a passed info into this function"
   print ("Name: ", name, "Age ", age)
   return

printinfo( age = 22, name = "Maxsu" )
printinfo( name = "Minsu" )

可变长度参数

def printinfo( arg1, *vartuple ):
    "This prints a variable passed arguments"
    print ("Output is: ", arg1)
    for var in vartuple:
      print (var, )
    return

printinfo( 10 )
printinfo( 70, 60, 50 )

匿名函数

sum = lambda arg1, arg2: arg1 + arg2

print ("Value of total : ", sum( 10, 20 ))
print ("Value of total : ", sum( 20, 20 ))