[Python知识库]#python学习笔记（二）#变量、表达式、语句

目录

1 Values and types

2 Variables

3 Statement

?4 Operators and operands

5 Input statement

6 Comments

1 Values and types

▲integer 整数：如2

▲float 浮点数：如4.6

▲string 字符：’Jackson Yee‘，’123‘

type() 用于指示数据的类型

>>> type(2)
<class 'int'>
>>> type(4.6)
<class 'float'>
>>> type('Jackson Yee')
<class 'str'>
>>> type('123')
<class 'str'>

2 Variables

A variable is a name that refers to a value

变量表示值的名称

An assignment statement creates new variables and gives them values

用赋值语句创建变量和它的值，之后可用变量来取出对应的数值

>>> a=2
>>> b='I am iron man'
>>> print(a,b)
2 I am iron man
>>> type(a)
<class 'int'>
>>> type(b)
<class 'str'>

▲变量名的要求：

（1）可以包含数字、字母和下划线?

（2）不能以数字开头

（3）不能空格，常用下划线来连接，如my_value

（4）不能使用reserved words

?（5）尽可能mnemonic：有助于记忆和理解程序

3 Statement

A statement is a unit of code that the Python interpreter can execute

语句是python可执行的一个单元（如输出语句、赋值语句等）

4 Operators and operands

▲operators 运算符：+、-、*、/、**(幂次）、//（商取整）、%（商取余）

>>> 1+2
3
>>> 3-2
1
>>> 2*3
6
>>> 3/2
1.5
>>> 7//2
3
>>> 7%2
1

?注意：python2里的/是商取整，即7/2=3

?▲计算顺序：从左到右，Parentheses（括号）>?Exponentiation （**）>Multiplication and Division（*/）> Addition and substraction (+-）

▲用于字符的运算符：concatenation （+）、Multiplication （*)

>>> print('hello'+'world')
helloworld
>>> print('hello'*3)
hellohellohello

5 Input statement

Python provides a built-in function called input that gets input from the keyboard. When this function is called, the program stops and waits for the user to type something. When the user presses Return or Enter, the program resumes and input returns what the user typed as a string.

函数input() 用于从键盘输入内容，用户按回车结束输入，输入的数据类型为字符

You can pass a string to input to be displayed to the user before pausing for input

括号内加入字符串可以向用户提示需要输入的内容

>>> name = input('What is your name?\n')
What is your name?
Chuck
>>> print(name)
Chuck

▲\n表示newline换行?

▲输入的内容为字符类型，如需进行数值计算需使用int()或float()进行类型转换

hr=input('Enter Hours:')
rt=input('Enter Rate:')
pay=float(hr)*float(rt)
print('Pay:',round(pay,1))

?运行结果

C:\Users\123\Desktop\python\ex2>python 2.py
Enter Hours:35
Enter Rate:2.75
Pay: 96.25

6 Comments

采用#对代码进行注解，python不会运行#之后的内容

#a python example
hr=input('Enter Hours:')#get hours from users
rt=input('Enter Rate:')#get Rate from users
pay=float(hr)*float(rt)#calculate Pay
print('Pay:',round(pay,1))#print pay