python data types and related utility functions

This series of examples of the use of python3.x, modified: 2019-09-03,23: 03:36

python in a "object reference" to store data in order to express the data objects, each object has a status, objects and values.

Utility functions:

• id (): see variable id address
• type (): Object Type View
• input (): Get the type of the variable character string input by the user
• eval (): used to perform a string expression, and returns the value of the expression. Used in conjunction with input (), obtaining the value of a continuous variable
• To exchange variables: x, y = y, x

num1, num2, num3 the eval = (INPUT ( " input three numbers separated by commas intermediate: " )) 

the try :
     Print (num1, num2, num3)
 the except Exception AS E:
     Print ( " error: " , E) 

running results: 
input three numbers separated by commas intermediate: 17, 18, 19 
17. 19 18

 

 

Common Python built-in types:

1. Value Type (Numeric Types): comprising int (integer), float (float), complex (complex)
2. Sequence type (Sequence Types): There str (string), list (list), tuple (tuple)
3. Iterative type (Iterator Types): to provide a container used for loop iterations
4. Collection type (Set Types): with a set (set variable) and frozenset (fixed or immutable collection set)
5. Mapping type (Mapping Types): Only dict (dictionary)

type of data

1. Integer type:

• Integer Interger:

　　　　Hex conversion functions:

• • bin (int): Decimal Binary turn, converted data will be prefixed with the character 0b
  • oct (int): decimal octal turn, converted data will be prefixed 0o character
  • hex (int): Decimal Binary turn, the data will be converted to character prefix 0x
  • int (s, base): to convert the string s base parameter according to the decimal value
  • format (value [, format_spec]): This function is used to convert other binary decimal (prefix character is removed)

= 255 dec_num   # decimal 
Print (bin (dec_num))   # binary output "0b11111111" 
Print (the OCT (dec_num))   # octal output "0o377" 
Print (hex (dec_num))   # hexadecimal output "0xff" 

bin_num = ' 0B ' + ' 10101 ' 
Print (int (bin_num, 2))   # binary decimal output 21 is 

NUM = 78   # decimal 
Print (the format (NUM, ' B ' ))   # outputs a binary string "1.00111 million" 
Print (the format (NUM, 'O' ))   # Output octet string "1 16" 
Print (the format (NUM, ' X ' ))   # output hex string "4e"

• Boolean Boolean:

　　　　Bool (Boolean) int subclass can be used BOOL () function. It has only two values ​​True and False.

• • True: 1 may be used to represent the values
  • False: value 0, special object None, an empty string, an empty list, empty tuple returns False 　　　　　　

2. floating-point type:

• Decimal (float):

　　　　Common functions:

• • float (): cast to float
  • fromhex (): Object methods, hexadecimal to decimal floating point
  • hex (): class method returns a string of hexadecimal floating point
  • is_integer (): class method of determining whether an integer, if a scale of zero, Return True

= 71.235 float_num   # define float 
float_num_hex float_num.hex = ()   # Returns a string of hexadecimal floating point 
Print (float_num_hex)   # output "+ 0x1.1cf0a3d70a3d7p. 6" 
Print (float.fromhex (float_num_hex))   # rpm back to the decimal number 71.235

 

　　　　Special floating-point numbers:

　　　　float ( 'nan'), float ( 'Infinity'), float ( '- inf') are three special floating point numbers, representing the non-digital (Not a number), infinity (Infinity), negative infinity (Negative Infinity)

　　　　Whether using standard math library module isNaN () determines whether the data is a NaN, isinf () determines inf data or -inf

• Complex (complex):

　　　　complex (re, im): re is the real, the real number; Imagine IM is imaginary, the imaginary part of the character plus the need to 'j' or 'J'

6J. 5 = + complex_num
 Print (type (complex_num))   # output <class 'Complex'> 
Print (complex_num.real)   # outputs the real part 5.0 
Print (complex_num.imag)   # output an imaginary part 6.0

 

• More precise Decimal Type:
  • Decimal type need to import using the decimal module
  • The Decimal () function can be specified to a string of significant digits, Decimal plurality of data are added, and the sum of the number of significant digits in the maximum significant digits; product of multiplying the number of significant digits is valid multiplier the sum of digits
  • getcontext (): Get the recording Decimal arithmetic defined environment, such as accuracy, rounding rules. getcontext (). prec of accuracy, getcontext (). rounding as the rounding rule

from decimal Import * Print (a Decimal (10/3)) # output 3.333333333333333481363069950020872056484222412109375 
NUM_1 = a Decimal ( ' 0.125 ' ); NUM_2 = a Decimal ( ' 8.8888 ' ) # string parameter to specify the number of significant digits Print (NUM_1 NUM_2 +)   # output 9.0138 Print (NUM_1 * NUM_2)   # output 1.1111000 Print (getContext (). prec)   # returns the accuracy of the output 28 
getContext (). prec. 3 =   # setting accuracy Print (NUM_1 NUM_2 +)   # output 9.01 Print








(getContext (). a Rounding)   # Returns the rounding rule output ROUND_HALF_EVEN 
getContext (). ROUND_FLOOR a Rounding =   # Set the rounding rules to negative infinity rounding 
Print (NUM_1 * NUM_2)   # Output 1.11

 

3. Score type:

•  Using a fractional function, you need to import the module fractions. Fractions () method is as follows

　　　　　Fraction(numerator, denominator)：

• • numerator: Molecular, the default value is 0
  • denominator: the denominator, the default value is 1
  • Whether or molecular denominator, use only a positive or negative integer, otherwise an error
• Fraction () method will automatically reduce fractions, but the parameters can not be mixed floating point and integer, otherwise an error TypeError
• With Fraction () method can be fractional arithmetic addition or multiplication

from the fractions are Import Fraction 

NUM_1 = Fraction (12, 36)   # define a variable fraction of the molecules 12, the denominator 36 
NUM_2 Fraction = (. 3,. 7 )
 Print (NUM_1 NUM_2 +)   # adder output 16/21 
Print (NUM_1 * NUM_2)   # multiplication output 1/7 
num_3 Fraction = (2.1,. 3) # error: error: both arguments should be rational instances ( two parameters should be a rational number) [way as the computer stores floating-point numbers, floating point numbers can be stored accurately]

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