Python3 Numbers

Python numeric operations

The Python interpreter can be used as a simple calculator: you can enter an expression in the interpreter that outputs the value of the expression.

The syntax + an * expression is straight- and - , / and / as in many 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 be different on different machines. We'll then cover controlling the output of floating-point operations.

In integer division, division / always returns a floating point, and if you only want to get the result of an integer and discard the possible fractional part, you can use // :

>>> 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: // of integer types is obtained is related to the data type of the denominator molecule.

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

The equal sign = used to assign a value to a variable. After the assignment, the interpreter does not display any results except for the next prompt.

>>> width = 20
>>> height = 5*9
>>> width * height
900

Python can use ** to perform power operations:

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

The variable must be "defined" (that is, given a value to the variable) before it can be used, or an error will occur:

>>> # 尝试访问一个未定义的变量
... n
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'n' is not defined

Floating points are fully supported;

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

In interactive mode, the result of the last expression that is output is assigned to the variable . This makes it easier for you to use Python as a desktop calculator for subsequent calculations, such as:

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

Here, the variable should be treated as a read-only variable by the user. Don't explicitly assign it a value -- you'll create a separate local variable with the same name and mask the functionality of the built-in variable.