Python--变量/运算符/表达式

1.python变量

       python变量名称只是用来引用内存中存储数据的标签；内存中相同的存储数据可以有多个标签，即多个变量名称。

变量名有字母、数字、下划线组成，数字不能开头，不可以使用关键字。

变量赋值：变量声明和定义的过程。eg:a=1，id(a)获取a的地址。

2.python运算符与表达式

       —赋值运算符：=、+=、-=、*=、/=、%=

       —算术运算符：+、-、*、/(实数除法)、//(整数除法)、%(求余数)、**(求幂运算，2**3=8)

user1@ubuntu:~$ su
Password: 
root@ubuntu:/home/user1# cd ~
root@ubuntu:~# cd csvtpy/
root@ubuntu:~/csvtpy# python
Python 2.7.3 (default, Apr 10 2013, 06:20:15) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 1+1
2
>>> 3-2
1
>>> 3*4
12
>>> 4/2
2
>>> 3/2
1
>>> 3.0/2
1.5
>>> 3.0//2
1.0
>>> 17/6
2
>>> 17%6
5
>>> 3**2
9
>>> 3**3
27
>>> a33=3**3
>>> a33
27
>>> print a33
27
>>> a33-12
15
>>> a15=a33-12
>>> a15
15
>>> a=100
>>> a-50
50
>>> b=a-50
>>> b
50
>>> a
100
>>> a=a-50
>>> a
50
>>> a-=50
>>> a
0
>>> a+=20
>>> a
20
>>> a*=3
>>> a
60
>>> a/=2
>>> a
30
>>> a%=4
>>> a
2
>>> 

四则运算器：

root@ubuntu:~/csvtpy# vim 3.py
root@ubuntu:~/csvtpy# python 3.py
5
1
6
1
root@ubuntu:~/csvtpy# vim 3.py
root@ubuntu:~/csvtpy# python 3.py
5
2
52
Traceback (most recent call last):
  File "3.py", line 6, in 
    print a-b
TypeError: unsupported operand type(s) for -: 'str' and 'str'
root@ubuntu:~/csvtpy# vim 3.py
root@ubuntu:~/csvtpy# python 3.py
5
2
7
3
10
2
root@ubuntu:~/csvtpy# vim 3.py
root@ubuntu:~/csvtpy# python 3.py
please input num1:8
please input num1:9
17
-1
72
0
root@ubuntu:~/csvtpy# vim 3.py
root@ubuntu:~/csvtpy# python 3.py
please input num1:3
please input num2:5
8
-2
15
0
root@ubuntu:~/csvtpy# 


3.py里面的内容：
#!/usr/bin/python
a=int(raw_input("please input num1:"))
b=int(raw_input("please input num2:"))

print a+b
print a-b
print a*b
print a/b

       —关系运算符：<、>、<=、>=、!=、== (均返回bool值)

>>> 1<2
True
>>> 3<1
False
>>> 3>2
True
>>> 3>5
False
>>> 3!=5
True
>>> 3!=3
False
>>> 3==3
True
>>> 3==3.0
True
>>> 3==33
False
>>>

       —逻辑运算符：and、or、not (均返回bool值)

>>> 1>2 2<3
  File "", line 1
    1>2 2<3
        ^
SyntaxError: invalid syntax
>>> 1>2 and  2<3
False
>>> 5>2 and  2<3
True
>>> 5>2 and  2>3
False
>>> 5<2 and  2>3
False
>>> 
>>> 1>2 or  2<3
True
>>> 5<2 and  5<3
False
>>> 
>>> 1>2
False
>>> not 1>2
True
>>> 

表达式是将不同数据(包括变量、函数)，用运算符按一定规则连接起来的一种式子。

user1@ubuntu:~$ su
Password: 
root@ubuntu:/home/user1# cd ~
root@ubuntu:~# cd csvtpy/
root@ubuntu:~/csvtpy# python
Python 2.7.3 (default, Apr 10 2013, 06:20:15) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> a=3
>>> a
3
>>> b=5
>>> b
5
>>> 3+5
8
>>> a+b
8
>>> a1=1
>>> a_1=2
>>> _a_2=3
>>> a1
1
>>> a_1
2
>>> _a_2
3
>>> _a3=3
>>> _a3
3
>>> a=33
>>> a
33
>>> a=44
>>> a
44
>>> id(a)
24767352
>>> a=33
>>> id(a)
24765624
>>> jb=23
>>> print jb
23
>>> jb=23+2
>>> print jb
25
>>> yd=45
>>> yd=kao
Traceback (most recent call last):
  File "", line 1, in 
NameError: name 'kao' is not defined
>>> yd='kao'
>>> print yd
kao
>>> HoursPerDay=24
>>> MinutesPerHour=60
>>> DaysPerWeek=7
>>> TotalMinutesPerWeek=DaysPerWeek*HoursPerDay*MinutesPerHour
>>> print TotalMinutesPerWeek
10080
>>> HoursPerDay=26
>>> TotalMinutesPerWeek=DaysPerWeek*HoursPerDay*MinutesPerHour
>>> print TotalMinutesPerWeek
10920
>>> 

以下图像来自中谷教育Python视频教学截图