Python，0a

 python  整数，浮点型，转换int，float，长度限定

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 1 # Arithmetic expressions - numbers, operators, expressions

 2 

 3 print 3, -1, 3.14159, -2.8

 4 

 5 # numbers - two types, an integer or a decimal number

 6 # two corresponding data types int() and float()

 7 

 8 print type(3), type(3.14159)

 9 print type(3.0)

10 

11 

12 # we can convert between data types using int() and float()

13 # note that int() takes the "whole" part of a decimal number and doesn't round

14 # float() applied to integers is boring

15 

16 print int(3.14159), int(-2.8)

17 print float(3), float(-1)

18 

19 

20 # floating point number have around 15 decimal digits of accuracy

21 # pi is 3.1415926535897932384626433832795028841971...

22 # square root of two is 1.4142135623730950488016887242096980785696...

23 

24 # approximation of pi, Python displays 12 decimal digits

25 

26 print 3.1415926535897932384626433832795028841971

27 

28 # appoximation of square root of two, Python displays 12 decimal digits

29 

30 print 1.4142135623730950488016887242096980785696

31 

32 # arithmetic operators

33 # +  plus  addition

34 # -  minus  subtraction

35 # *  times  multiplication

36 # /  divided by  division

37 # **    power  exponentiation

38 

39 print 1 + 2, 3 - 4, 5 * 6, 2 ** 5

40 

41 # Division in Python 2

42 # If one operand is a decimal (float), the answer is decimal

43 

44 print 1.0 / 3, 5.0 / 2.0, -7 / 3.0

45 

46 # If both operands are ints, the answer is an int (rounded down)

47 

48 print 1 / 3, 5 / 2, -7 / 3

49 

50 

51 # expressions - number or a binary operator applied to two expressions

52 # minus is also a unary operator and can be applied to a single expression

53 

54 print 1 + 2 * 3, 4.0 - 5.0 / 6.0, 7 * 8 + 9 * 10

55 

56 # expressions are entered as sequence of numbers and operations

57 # how are the number and operators grouped to form expressions?

58 # operator precedence - "please excuse my dear aunt sallie" = (), **, *, /, +,-

59 

60 print 1 * 2 + 3 * 4

61 print 2 + 12

62 

63 

64 # always manually group using parentheses when in doubt

65 

66 

67 print 1 * (2 + 3) * 4

68 print 1 * 5 * 4