Python study notes eleven _ function return multi-value, list generation, loop multi-variable, input parameter format declaration

1. Functions that return multiple values

1. If the function returns multiple values, it will put these values ​​into a tuple 2. If the
function returns multiple values, it can also be received by multiple variables

def say():
    num1 = 1 
    num2 = 2 
    num3 = 3
     return num1,num2,num3
 print ( say()) #If the function returns multiple values, it will put these values ​​into a tuple, (1, 2, 3 ) 
res1,res2,res3 = say() #When multiple values ​​are returned, multiple variables can be used to receive print (res1) # 1 print (res2) # 2 print (res3 ) # 3

2. List Compilation

l = [i for i in range(1,101,2)]

List comprehensions, which can only be used in lists

Write the loop first, then take out the i in the loop, you can do some simple operations (zero-fill, convert to string, etc.)

import random
red_num = random.sample(range(1,34),6)
new_num = []
# for num in red_num:
#     tmp = str(num).zfill(2)
#     new_num.append(tmp)
new_num = [str(num).zfill(2) for num in red_num]#列表生成式
print(new_num)#['16', '20', '07', '18', '13', '01']

Generate odd numbers up to 100

l = [i for i in range(1,101,2)] #The outside is [] is a list 
print (l)

3. Generator

l1 = (i for i in range(1,11,2))

Replace the [ ] in the list comprehension with ( ), and printing the generator itself will display the generator instead of the list

l = [i for i in range(1,11,2)] #The outside is [] is a list 
#The space is exchanged for time, the memory usage is large, but there is no need to calculate the cpu 
#list It is to put all the elements In the memory, 5 memory spaces will be applied here 
print (l) # [1, 3, 5, 7, 9] 
l1 = (i for i in range(1,11,2)) #outside is () If it is generator 
# generator generator saves memory than list, it calculates an element according to the rules each time it loops, and puts it in memory 
# generator performance is better than list, only applies for one piece of memory space, each time Call and calculate according to the rules 
print (l1) # <generator object <genexpr> at 0x00000000030FE4C0> 
for i in l1:
     print (i) #1 3 5 7 9

4. Ternary expressions

c = a if a > b else b

a = 5 
b = 3
 # if a > b: 
#      c = a 
# else: 
#      c = b 
c = a if a > b else b # if a is greater than b, a = c, otherwise c = b 
print (c )

Five, loop two-dimensional array

l = [
    [1,2,3,4],
    ['a','b','c','d']
]
for a,b,c,d in l: #There are multiple elements in the two-dimensional array, you can loop like this print (a) # 1,a print (b) # 2, b
    
    

6. Declaration input format

Just for code readability and does not cast types

def my(name:str): #Tell others that name is str, but it will not be forced to convert, l:list tells others that the input is list 
   print (name)
my('hello')
my([ ' 123 ' ,123]) #The input parameter can also be a list, ['123', 123]