Lecture1：Goals of the course; what is computation; introduction to data types, operators, and variables

Python

• High （√） VS. low
• General （√） VS. targetted

• Interpreted （√） VS. compile

  1. Syntax语法：what are legal expressions
     “cat dog boy “
  2. Static semantics 静态语义：which programs are meaningful
     “   My desk is Suson“
  3. Full semantics 完整语义：what does program mean
     what will happen when i run it

Operation
+ - * /

>>>'a'*3'aaa'>>>3/50>>>3**327
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Variables

>>> a = 3>>> print a3
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Lecture2：Operators and operands; statements; branching, conditionals, and iteration

Operators and operands

>>> 'ab' + 'c''abc'>>> 3 + 'c'Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'str'>>> str(3) + 'c''3c'
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• type conversion 类型转换  str(3)
• type checking 类型检查  weak VS. strong typing
  TypeError: unsupported operand type(s) for +: ‘int’ and ‘str’
• type discipline
• operation precedence 算符优先
  * >> / >> + -    when is doubt， use ()

>>> 'a' < 3False>>> 4 + '3'True>>> 9／51>>> 9％54>>> 3＋4＊523
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• Variables has a value－－Assignment x = 3

• type of Variables－－get from value
  Dynamic types 动态类型
  x = ‘abc’

  don’t change types arbitrarily 不要反复无常的改变变量类型

• Variables used any place it’s legal to use value

  ---

statements

• statements = legal commands that Python can interpret
• print, assignment
  

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branching 分支

• change the order of instructions based on some test (usually a value of a variable)
• Syntax
  冒号colon :  begin a sequence of instructions
  identifies a block of instructions.

冒号: start
carriage 回车 is end
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x = 15if（x/2）* 2 == x:    print 'Even'else: print 'Odd'
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conditionals 条件

＃ if语句可嵌套if <some test> :
    Block of instructions.else: 
    Block of instructions.
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• Boolean combination：AND, OR, or NOT

iteration 迭代 or loops 循环

# y ＝ x的平方y = 0x = 3itersLeft = xwhile(itersLeft>0) :
    y = y + x
    itersLeft = itersLeft -1print y