Python loop structure (for-in)

cyclic structure (for-in)

• Description: Also a loop structure, often used to traverse strings, lists, tuples, dictionaries, etc.

• Format:

  Y:
  Loop body

  Execution process: X in turn represents an element in Y, traversing through all elements loop end

• Example 1: Traversing a string

  
  ' I love your more than I can say '
  S
  print (i) 

• Example 2: Traversing a list

   l = [ Goose Goose Goose,  "Song to Heaven", " Hoe wo Day copse ',  ' spring planting a grain of millet ' 
    ? 
    for i in l: 
       print (i) 
    ? 
    # can get the following table, enumerate each loop can get the following table and elements 
    for i, v in enumerate (l): 
       print (i, v)              

• Example 3: Traversing a dictionary

  
  D = {' A ':' Apple ',' B ':' Banana ',' C ':' Car ',' d ':' Desk '}
  ?
  ForKeyin d: 
       # Traversing the dictionary is the key 
       print (key, d.get (key)) 
    ? 
    # for key, value in D.items (): 
    # two ways equivalent D.items () <=> Dict.items (d) 
    for key, value in dict. items (d): 
        Print (key, value)        

• List-Generated

  • Iterate objects: Lists, tuples, dictionaries, and so on are iterative objects, which are objects that can be traversed

  • Range, use the following:

  
  Printrange (10)) 
    # You can build an iterative object that starts from 0 to 10 consecutive integers 
    print (range ( 0, 10)) 
    ? 
    # can traverse 
    for i in range (10): 
       print (i) 
    ? 
    # cast to list 
    print (list ( range (1, 11)))      

  • List generation: Quickly generate lists with specific rules

  
  # List-Generated
  Print ([IForIInchRange1,11)])
  Print ([I*2ForIInchRange1,11)])
  Print ([I*IFori in range (1 , 11)]) 
    print ([str (i) for i in range (1, 11)]) 
    print ([i for i in range (1 , 11) if i % Span class= "Cm-number" >2 = = 0])          

• Multiple loops: A nested loop in a loop

  • Example 1: Enter an integer from the terminal to print as a shape:

  
  n =intInput' Please enter an integer: ')
  ?
  ‘‘‘
  1
  0 S
  1 2 3
  1 2 3 4
  ...
  1 2 3 4 ... n
  ‘‘‘
  ?
  ‘‘‘
  j = 1
  While J <= N:
  i = 1
  While I <= J:
  Print (I, end= ")
  i + = 1
  Print ()
     J + = 1 
     "
    ? 
    for i in range (1, n +1): 
       for j in range (1, i+1): 
            Print (j, end= ") 
       print ()            

  • Example 2: Print a 99 multiplication table

  
  Fori in range (1 , 10): 
       for j Span class= "Cm-keyword" >in range (1, i< Span class= "Cm-operator" >+1): 
            print ( ' {}x{}={} '.  Format (j, i, j *i), end= ') 
       print ()         

  • Example 3: List sorting (selection method)

  
  L = [1,9,4,2,0,8,3,7]
  ?
  # Get length
  n =LenL
  ?
  # The outer loop is used to control the number of loops in the loop, and each circle can determine the position of an element
  # Make sure n elements start with only a n-1 circle
  ForIInchRangeN-1):
  # The Inner loop is used to compare the size of the interchange element, a circle to determine an element
  ForJInchRangeI+1, n): 
            # if not appropriate 
           if l[i" > l[j]: 
               # Exchange two variables 
               l[i], l[j] = l[j], l[i] 
    ? 
    print (l)          

  • Practice:

    2. Sort a list by using bubbling

       
       1. Bubble: Each time comparing the adjacent two elements, not suitable for exchange, and then backward, a circle down can be determined an element
       2. Need to use a double loop, the outer loop control loop number of loops, the inner layer control how to exchange a circle

    4. Traverse List, Print: My name is XXX, this year yyy year old, I come from zzz, the data are as follows

       lt = [

       
         {' name ': ' Xiao Wang ', ' age ': ' Info ': [(' Phone ', ' 123 '), (' Dizhi ', ' Guangzhou ')},
         {' name ': ' Small Fang ', ' age ': +, ' info ': [(' Phone ', ' 789 '), (' Dizhi ', ' Shenzhen ')},
         {' name ': ' Du ', ' age ': ' Info ': [(' Phone ', ' 567 '), (' Dizhi ', ' Beijing ')},
         {' name ': ' Little Meng ', ' age ':--' info ': [(' Phone ', ' ' "') ' (' Dizhi ', ' Shanghai ')},
         {' name ': ' Little Joe ', ' age ': +, ' info ': [(' Phone ', ' 111 '), (' Dizhi ', ' Henan ')},
       ]

    6. Enter two integers from the terminal m,n, print the M*n table, such as: 2, 5, print the following effect

       
       1 2 3) 4 5
       6 7 8) 9 10

Python loop structure (for-in)