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Python3 Number (Number)

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Python3 Number (Number)

Python numeric data types are used to store numeric values.

The data type is not allowed to change, which means that if the value of the numeric data type is changed, the memory space will be reallocated.

The following instances of Number objects will be created when variables are assigned:

var1 = 1
var2 = 10

You can also delete references to some number objects using the del statement.

The syntax of the del statement is:

del var1[,var2[,var3[....,varN]]]

You can remove references to single or multiple objects by using the del statement, for example:

del var
del var_a, var_b

Python supports three different numeric types:

Integer (int) - Often referred to as an integer or integer, is a positive or negative integer without a decimal point. The Python3 integer has no size limit and can be used as a Long type, so Python3 does not have the Python2 Long type. Boolean (bool) is a subtype of integer.
Floating-point type (float) - floating-point type consists of an integer part and a fractional part, and the floating-point type can also be expressed in scientific notation (2.5e2 = 2.5 x 102 = 250)
Complex number ((complex)) - A complex number consists of a real part and an imaginary part, which can be represented by a + bj, or complex(a, b). The real part a and imaginary part b of a complex number are both floating-point types.

We can represent integers using hexadecimal and octal:

>>> number = 0xA0F # 十六进制
>>> number
2575

>>> number=0o37 # 八进制
>>> number
31

int	float	complex
10	0.0	3.14y
100	15.20	45.j
-786	-21.9	9.322e-36j
080	32.3e+18	.876j
-0490	-90.	-.6545+0J
-0x260	-32.54e100	3e+26J
0x69	70.2E-12	4.53e-7j

Python supports complex numbers. A complex number consists of a real part and an imaginary part. It can be represented by a + bj, or complex(a, b). The real part a and the imaginary part b of a complex number are both floating-point types.

Python numeric type conversion

Sometimes, we need to convert the built-in type of data. For data type conversion, you only need to use the data type as the function name.

int(x) converts x to an integer.
float(x) converts x to a floating point number.
complex(x) converts x to a complex number with x as the real part and 0 as the imaginary part.
complex(x, y) converts x and y to a complex number with real part x and imaginary part y. x and y are numeric expressions.

The following example converts the floating-point variable a to an integer:

>>> a = 1.0
>>> int(a)
1

Python number crunching

The Python interpreter can be used as a simple calculator, you can enter an expression into the interpreter, and it will output the value of the expression.

The syntax of expressions is straightforward: +, -, * and /, as in other languages such as Pascal or C. For example:

>>> 2 + 2
4
>>> 50 - 5*6
20
>>> (50 - 5*6) / 4
5.0
>>> 8 / 5  # 总是返回一个浮点数
1.6

Note: The results of floating-point operations may vary on different machines.

In integer division, division / always returns a floating-point number. If you only want the integer result and discard possible fractional parts, you can use the operator // :

>>> 17 / 3  # 整数除法返回浮点型
5.666666666666667
>>>
>>> 17 // 3  # 整数除法返回向下取整后的结果
5
>>> 17 % 3  # ％操作符返回除法的余数
2
>>> 5 * 3 + 2 
17

Note: // The number obtained is not necessarily an integer type, it is related to the data type of the denominator and numerator.

>>> 7//2
3
>>> 7.0//2
3.0
>>> 7//2.0
3.0
>>>

The equals sign = is used to assign values to variables. After the assignment, the interpreter will not display any results except at the next prompt.

>>> width = 20
>>> height = 5*9
>>> width * height
900
Python 可以使用 ** 操作来进行幂运算：

>>> 5 ** 2  # 5 的平方
25
>>> 2 ** 7  # 2的7次方
128

A variable must be "defined" (that is, assigned a value) before it can be used, otherwise an error will occur:

>>> n   # 尝试访问一个未定义的变量
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'n' is not defined
不同类型的数混合运算时会将整数转换为浮点数：

>>> 3 * 3.75 / 1.5
7.5
>>> 7.0 / 2
3.5

In interactive mode, the last output expression result is assigned to the variable _. For example:

>>> tax = 12.5 / 100
>>> price = 100.50
>>> price * tax
12.5625
>>> price + _
113.0625
>>> round(_, 2)
113.06

Here, the _ variable should be considered read-only by the user.

math function

function	return value (description)
abs(x)	Returns the absolute value of a number, such as abs(-10) returns 10
ceil(x)	Returns the upper integer of the number, such as math.ceil(4.1) returns 5
cmp(x, y)	Returns -1 if x < y, 0 if x == y, and 1 if x > y. Deprecated in Python 3, use (x>y)-(x<y) instead.
exp(x)	Returns the x power of e (ex), such as math.exp(1) returns 2.718281828459045
fabs(x)	Returns the absolute value of a number as a floating point number, such as math.fabs(-10) returns 10.0
floor(x)	Returns the rounded integer of a number, such as math.floor(4.9) returns 4
log(x)	Such as math.log(math.e) returns 1.0, math.log(100,10) returns 2.0
log10(x)	Returns the logarithm of x in base 10, such as math.log10(100) returns 2.0
max(x1, x2,…)	Returns the maximum value of the given argument, which can be a sequence.
min(x1, x2,…)	Returns the minimum value of the given argument, which can be a sequence.
modf(x)	Returns the integer part and fractional part of x. The numerical signs of the two parts are the same as x, and the integer part is expressed in floating point.
pow(x, y)	The value after x**y operation.
round(x [,n])	Returns the rounded value of the floating-point number x, or the number of digits rounded to the decimal point if n is given. In fact, it is accurate to say that the reserved value will be reserved to the end closer to the previous one.
sqrt(x)	Returns the square root of the number x.

random number function

Random numbers can be used in mathematics, games, security and other fields, and are often embedded in algorithms to improve algorithm efficiency and program security.

Python includes the following commonly used random number functions:

function	describe
choice(seq)	Randomly pick an element from the elements of the sequence, such as random.choice(range(10)), randomly pick an integer from 0 to 9.
randrange ([start,] stop [,step])	Obtain a random number from the set within the specified range and incremented by the specified radix, the default value of the radix is 1
random()	Randomly generate the next real number, which is in the range [0,1).
seed([x])	Change the seed of the random number generator. If you don't understand its principle, you don't have to set the seed specifically, Python will help you choose the seed.
shuffle(lst)	randomize all elements of a sequence
uniform(x, y)	Randomly generate the next real number in the range [x,y].

Trigonometric functions

Python includes the following trigonometric functions:

function	describe
acos(x)	Returns the arccosine radian value of x.
asin(x)	Returns the arcsine of x in radians.
time(x)	Returns the arctangent of x in radians.
atan2(y, x)	Returns the arctangent of the given X and Y coordinates.
cos(x)	Returns the cosine of x in radians.
hypot(x, y)	Returns the Euclidean norm sqrt(x x + y y).
sin(x)	Returns the sine of x in radians.
tan(x)	Returns the tangent of x in radians.
degrees(x)	Convert radians to angles, such as degrees(math.pi/2), return 90.0
radians(x)	Convert angles to radians

mathematical constant

constant	describe
pi	The mathematical constant pi (pi, generally expressed in π)
e	The mathematical constant e, e is the natural constant (natural constant).

[Python] Python Series Tutorials--Python3 Numbers (Number) (10)