Two decimal places reserved in Python

I ran into a problem writing a program today about how to control floating-point numbers only show two digits after the decimal point, the normal idea is to use the round function, for exampleround(a, 2)，但是在面对下面的问题时候round就不太好用了

>>> a=13.949999999999999
>>> Round (A, 2)
13.949999999999999

On the Internet to check the information, there are netizens to provide a way

Print ('%.2f '%a)

>>>13.95

Alternatively, you can use Trunc (a,2) to intercept the function

>>>13.94

You can also use the decimal

Decimal. The decimal type is a data type that satisfies high-precision calculations in Python and imports the decimal package with import

Define the decimal data type:

1 cannot be defined in the way that the literal value is used

2 are defined in the following ways:

>>> Import decimal >>> x = Decimal. Decimal (87345) >>> x decimal (' 87345 ') >>> x = Decimal. Decimal (' 123.3344332566334 ') >>> x decimal (' 123.3344332566334 ') can be passed to a Decimal integer or string parameter, but cannot be a floating-point data, Because the floating-point data itself is inaccurate

If you need to convert from floating-point data to a decimal type, you might use the following methods

>>> x = Decimal. Decimal.from_float (127.3323)
>>> x
Decimal (' 127.332300000000003592504072003066539764404296875 ')

I had 3 questions pertaining to decimal arithmetic in Python, and all 3 of the which is best asked inline:

1)

FromImport,Decimal>>>().=6>>>Decimal' 50.567898491579878 '  1Decimal' 50.5679 '# How are this a precision of 6? If the decimal counts whole numbersas >>># Part of the precision, are that actually still precision?  >>>     and

2)

FromImport,Decimal>>>().=6>>>Decimal' 50.567898491579878 'Decimal' 50.567898491579878 '# shouldn ' t that has been rounded to 6 digits on instantiation?>>>Decimal' 50.567898491579878 '  1decimal ' 50.5679 ' >>>3)      

# now I want to save the value to my database as a ' total ' with 2 places.>>>FromImportDecimal>>># is the following the correct-to-get the value into 2 decimal places,>>># or is there a "better"?>>>=Decimal' 50.5679 'QuantizeDecimal' 0.00 '# Just wanted to see what's the value wasDecimal' 50.57 '()>>> Native test cases:    

[Python]View Plain copy

2. >>> Import Decimal
4. >>> x = Decimal. Decimal (87345)
6. >>> x
8. Decimal (' 87345 ')
10. >>> Print x
12. 87345
14. >>> from decimal import getcontext, decimal
16. >>> x = decimal (' 0.998531571219 '). Quantize (Decimal (' 0.00 '))
18. >>> x
20. Decimal (' 1.00 ')
22. >>> Print x
24. 1.00
26. >>> x = decimal (' 0.998531571219 '). Quantize (Decimal (' 0.0000 '))
28. >>> x
30. Decimal (' 0.9985 ')
32. >>> Print x
34. 0.9985
36. >>> y = decimal.from_float (0.998531571219)
38. >>> y
40. Decimal (' 0.99853157121900004700165709436987526714801788330078125 ')
42. >>> y = decimal.from_float (0.998531571219). Quantize (Decimal (' 0.0000 '))
44. >>> y
46. Decimal (' 0.9985 ')
48. >>> Print y
50. 0.9985
52. >>> f1 = 0.998531571219
54. >>> F1
56. 0.998531571219
58. >>> Type (F1)
60. <type ' float ' >
62. >>> F2 = str (f1)
64. >>> F2
66. ' 0.998531571219 '
68. >>> type (F2)
70. <type ' str ' >
72. >>>

Two decimal places reserved in Python