Python Learning _4_if_while_for

#条件语句 Loop Statements

#条件语句: The condition is met before execution

#语法 sentence patterns

#python代码的特点: Using indentation to control the level code is performed from top down

#1) Meet the criteria to execute if or other elif code

#2) must be if the start can be without elif but must have if

#3) If you have elif then elif must have conditional expressions

#4) There can be multiple elif in a conditional statement, only one if, an else

#5) You cannot add any expression after else inside a conditional statement

#最简单的句式
A = 1if a < 0    :print("A's value greater than 0")#If the expression is true  Execute the following code #If the expression after is false does not execute the following code   

#2: Upgrade Statement

A = 5
If a > 10:
     Print ("A's value is greater than 0")
Elif A < 0:
    If a <-10:
        Print ("negative number ....") ")
    Print ("A's value is less than 0")
elif A = = 0:
    Print ("0000")
Else
    Print ("Done")

Small exercise: Late class questions

time = Int (input ("input the time:"))ifTime >0:ifTime <= 5:        Print("not late .")    elifTime <= 10:        Print("Shandao.")    Else:        Print("absenteeism.")Else:    Print("wrong input")

#循环语句 while loop while keyword

#语法: While conditional expression:

#代码块

The rules that #while execute first determine the condition after the while

#满足就执行while下面的代码块 finished executing the code block.

#继续判断while条件 meet and then execute again, not meet to do the cycle

#如何跳出死循环或者避免自己的代码出现死循环

#1) Set a good judgment condition, can not meet the conditions at the right time, jump out of the loop

#2) skillfully breaks the current loop with break

A = 0 while a > 0:    print("python test 6666")
Break
A = A-1

#练习题:

# use while loop in order greater than 10,9....0num = ten while num >= 0:    print' ' )    -= 1
#结果为: 10 9 8 7 6 5 4 3 2 1 0

#for cyclic single-layer cyclic multilayer loops

#for循环 to traverse the element's keyword for

#for item in data range: #字符串 A list of tuple dictionaries can also be other data types

list_1 = [' Don't leave ' ' little star ''tiger'  sha'] for in list_1:     # traversing elements will put in The elements in the subsequent data range are all taken over the    # essence: Get these values in turn    print(item)
The second way:
For item in range (LEN (list))
Print (List_1[item])

#问题: The For loop is executed several times by who decides-----> length of data

#遍历元组或字符串:

' Python8 '  for inch list_1:     Print  '666',' flowers ' hahaha ' ) for in tuple_1:    print(i)

#遍历字典:

dict_1 = {'age'sex'girl'}   for in dict_1:    print (key) #遍历字典里的键值对, printing key     Print (Dict_1[key]) #打印key对应的值

#字典名. Keys ()  gets the dictionary all key values
#字典名. VALUES ()  gets all the value values

#range function It can generate a sequence of integers of a specified range

#str () int () list ()

res = list (range (5)) #可强制转换为list

#range (m,n,k) m integer sequence of beginning n integer sequence ending with K step

Res_1 = List (range (1,5,1))  #1,2,3,4 res_2 = List (range (0,5,2))  #0,2,4 Res_3 = List (range (6, 0,-1))  #6,5,4,3,2,1 res_4 = List (range (6,0,-2))    #  6,4,2,

#嵌套循环 Two for loop there's a loop inside.

List_1 = [[1,2,3],[4,5,6]]# traverse this list: for in range (len (list_1)):      for in range (len (list_1[i))        :print(List_1[i][j])

Practice:

#遍历整个列表元素
L = [['Apple','Google','Microsoft'], ['Java','Python','Ruby','PHP'], ['Adam','Bart','Lisa'] ] forIinchRange (len (L)): forJinchRange (len (l[i)):Print(L[i][j])

Python Learning _4_if_while_for