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  • Python

    From:http://interactivepython.org/courselib/static/pythonds/Introduction/ControlStructures.html

    Control Structures

    As we noted earlier, algorithms require two important control structures: iteration and selection.

    • Iteration
      • while
    >>> counter = 1
    >>> while counter <= 5:
    ...     print("Hello, world")
    ...     counter = counter + 1
    
    
    Hello, world
    Hello, world
    Hello, world
    Hello, world
    Hello, world
      • for
    >>> for item in [1,3,6,2,5]:
    ...    print(item)
    ...
    1
    3
    6
    2
    5

    >>> for item in [1,3,6,2,5]:
    ...    print(item)
    ...
    1
    3
    6
    2
    5

    wordlist = ['cat','dog','rabbit']
    letterlist = [ ]
    for aword in wordlist:
    for aletter in aword:
    letterlist.append(aletter)
    print(letterlist)

    • Selection
    Selection statements allow programmers to ask questions and then, based on the result, perform different actions.
      • ifelse
    if n<0:
       print("Sorry, value is negative")
    else:
       print(math.sqrt(n))

    if score >= 90:
       print('A')
    else:
       if score >=80:
          print('B')
       else:
          if score >= 70:
             print('C')
          else:
             if score >= 60:
                print('D')
             else:
                print('F')


    if score >= 90:
       print('A')
    elif score >=80:
       print('B')
    elif score >= 70:
       print('C')
    elif score >= 60:
       print('D')
    else:
       print('F')
      • if
        if n<0:
           n = abs(n)
        print(math.sqrt(n))
         
      • list comprehension
    >>> sqlist=[]
    >>> for x in range(1,11):
             sqlist.append(x*x)
    
    >>> sqlist
    [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
    >>>


    >>> sqlist=[x*x for x in range(1,11)]
    >>> sqlist
    [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
    >>>
    >>> sqlist=[x*x for x in range(1,11) if x%2 != 0]
    >>> sqlist
    [1, 9, 25, 49, 81]
    >>>


    >>>[ch.upper() for ch in 'comprehension' if ch not in 'aeiou']
    ['C', 'M', 'P', 'R', 'H', 'N', 'S', 'N']
    >>>

     

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  • 原文地址:https://www.cnblogs.com/keepSmile/p/7879223.html
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