4.6 floating point number

4.6 Floating point numbers

Python The first data type ： character string , Shorthand for str.
Python The second data type ： Integers , The whole number is in English integer, Shorthand int.
Python The third data type ： Floating point numbers , The English name of a floating-point number is float, There is no shorthand for floating-point numbers .
float [fləʊt]： Floating point numbers .
Python Numbers without dots in are integers , Some numbers are floating point numbers .

The following numbers are floating point numbers .

a = 0.5
b = -0.5 
c = 1.0

#  Find the sum of two floating-point numbers 
0.2+0.2

【 Terminal output 】
0.4

#  Find the sum of two floating-point numbers 
0.2+0.1

【 Terminal output 】
0.30000000000000004

#  Find the product of two floating-point numbers 
0.2*0.2

【 Terminal output 】
0.04000000000000001

#  Find the product of two floating-point numbers 
2*0.2

【 Terminal output 】
0.4

Floating point calculation ：

#  Assign a value to a variable 
float_1 = 0.55
float_2 = 0.3

#  Find the sum of two floating-point numbers 
print(float_1+float_2)

【 Terminal output 】
0.8500000000000001

0.5+0.33 And why not 0.85 Well ？
As we all know, the operation of the computer is binary , Before the operation , The computer will first 0.55 and 0.3 Convert to binary , So the tail of the calculated value is one more 1.
This is not Python Key points of , Understanding can .
0.55( Decimal system ) = 0.1000110011001100110011001100110011001100110011001101( Binary system )
0.3( Decimal system ) = 0.0100110011001100110011001100110011001100110011001101( Binary system )

Exercises ：

ask ： Please tell me the following three data 【100】、【‘100’】、【100.0】 The data types are ：
answer ： Integers 、 character string 、 Floating point numbers .

summary

1、Python The first data type ： character string ,str.
2、Python The second data type ： Integers ,int.
3、Python The third data type ： Floating point numbers ,float.