Week Four: Good Programming Practices

1. Testing and Debugging

   

2. Classes of Tests

   • break program into modules
   • document constraints on modules
   • document assumptions
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3. Bugs

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4. Debugging

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5. Debugging Skills

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6. Exceptions

• Syntax: try;except;finally

      try:
          a = int(input("tell me one number:"))
          b = int(input("tell me another number:"))
          print(a/b)
          print('okay')
      except ValueError:
          print('Bug in user input.')
      except ZeroDivisionError:
          print("Can't divide by zero")
      finally
        print('Close')
      print('outside')
  

• Syntax: raise

  我们可以使用raise语句自己触发异常。

    # 定义函数
    def mye( level ):
        if level < 1:
            raise Exception,"Invalid level!"
            # 触发异常后，后面的代码就不会再执行
    try:
        mye(0)            # 触发异常
    except Exception,err:
        print 1,err
    else:
        print 2
  

• Use an assert statement to raise an AssertionError exception if assumptions not met.

  def avg(grades):
      assert not len(grades) == 0, 'no grades data'
      return sum(grades)/len(grades)#raises an AssertionError if it is given an empty list for grades; otherwise runs ok

• typically used to check inputs

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