1.变量
1.1变量作用
变量是用于存储数据
1.2变量定义规范
声明变量
name = "vita" pep8规范：等号两边要有空格
变量定义规则
- 变量名只能是字母、数字、下划线的任意组合
- 变量名的第一个字符不能是数字
- 程序关键字不能是数字，例如if else while等
变量命名习惯
驼峰体 AgeOfVita = 27 下划线 age_of_vita = 27
变量定义的low方式
变量名为中文、拼音 名字 = "vita" 变量名过长 qeqweqwe_qweqweqw_qwewqeq 变量名词不达意 a = 23
1.3常量
常量定义
常量即指不变的量，如pai 3.1415926 ,或在程序运行过程中不会改变的量。 Python中没有专门的语法定义常量，程序员约定用变量名全部大写代表常量。 python中可自定义一个不修改的常量的类。
AGE_OF_VITA = 27
Java中定义常量，修改该常量会报错
public static final String SUNDAY = "SUNDAY";
c语言中定义常量，修改该常量也会报错
const int count = 60;
变量与常量用法示例
在使用中变量和常量没什么区别
Python 2.7.16 (v2.7.16:413a49145e, Mar 4 2019, 01:37:19) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license()" for more information.
>>> a = 1
>>> b = a
>>> print(a)
1
>>> print(b)
1
>>> a=2
>>> print(a)
2
>>> print(b)
1
>>>
>>>
>>> A = 10
>>> B=A
>>> print(A)
10
>>> print(B)
10
>>> A=20
>>> print(A)
20
>>> print(B)
10
>>>
2.读取用户输入
name = input("please input your name:")
age = input("please input your age:")
hometown = input("please input your hometown:")
print("your name is:"+name
+ " your age is:"+age
+ " your hometown is:"+hometown)
运行
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
please input your name:vita
please input your age:27
please input your hometown:jl
your name is:vita your age is:27 your hometown is:jl
3.注释
本行注释
age = input("please input your age:") # age pep8规范：#号前面至少两个空格，后面一个空格
单行注释
hometown = input("please input your hometown:")
# print age pep8规范：#号前面无空格，后面一个空格
多行注释
"""
print age
name hometown
"""
'''
print age
name hometown
pep8规范：注释与下面的代码的空行不能多于两行
'''
print("your name is:"+name
+ " your age is:"+age
+ " your hometown is:"+hometown)
4.数据类型
4.1数字类型
4.1.1介绍
int(整型)
在32位机器上，整数的位数为32位，取值范围为-2**31~2**31 -1，即-2147483648~214748364
在64位系统上，整数的位数为64位，取值范围为-2**63~2**63-1,即-9223372036854775808~9223372036854775807
long(长整型)
跟C语言不同，Python的长整型没有指定宽度，即python没有限制长整数数值的大小，但实际上由于内存的限制，我们使用的长整数数值不可能无限大。
注意：
自从Python2.2起，如果整数发生溢出，Python会自动把int转换为long，所以现在在long数据后面不加字母L也不会导致严重后果了。
在Python3中没有int和long的区分了，全部都是int
除了int和long外，还有float浮点型，复数型
4.1.2Python2&3之int long
(venvP3) E:\PythonProject\python-test>python2
Python 2.7.16 (v2.7.16:413a49145e, Mar 4 2019, 01:37:19) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> type(2**4)
<type 'int'>
>>> type(2**65)
<type 'long'>
>>> quit()
(venvP3) E:\PythonProject\python-test>python3
Python 3.6.2 (v3.6.2:5fd33b5, Jul 8 2017, 04:57:36) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> type(2**4)
<class 'int'>
>>> type(2**65)
<class 'int'>
>>>
4.2字符串
在Python中，加了引号的字符就被认为是字符串
4.2.1字符串种类
Name = "vita" # 双引号
Age = "27" # age是字符串
AgeNum = 27 # age是int
Msg = 'My name is vita,i am 27 years old!' # 一对单引号
# 一对三个单引号
MsgThree = '''
My name is vita,
i am 27 years old!
'''
# 三个双引号
MsgDouThree = """
My name is vita,
i am 27 years old!
"""
4.2.2单引号，双引号，多引号的区别
单引号和双引号没有任何区别，只是在下面情况下需要考虑单双引号配合
Msg = "my name is vita,I'm 27 years old"
多引号的作用是多行字符串，需要使用多引号
# 一对三个单引号
MsgThree = '''
My name is vita,
i am 27 years old!
'''
# 三个双引号
MsgDouThree = """
My name is vita,
i am 27 years old!
"""
4.2.3字符串拼接
字符串可以进行“相加”和“相乘”运算
>>> name = "vita"
>>> age = "27"
>>> print("your name is:"+name+" your age is:"+age)
your name is:vita your age is:27
>>> print("v"*3)
vvv
字符串不能喝整数拼接
>>> name = "vita"
>>> age = 27
>>> print(name+age)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: must be str, not int
4.3布尔型
布尔型就两个值，true和false，主要用于逻辑判断
>>> a =3
>>> b = 5
>>> a>b
False
>>> a<b
True
4.4格式化输出
name = input("input your name:")
age = input("input your age:")
hometown = input("input your hometown:")
msg = '''
------the info of %s is ------
name: %s
age: %s
hometown: %s
------the info of end ------
''' % (name, name, age, hometown)
print(msg)
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
input your name:vita
input your age:27
input your hometown:jl
------the info of vita is ------
name: vita
age: 27
hometown: jl
------the info of end ------
4.5运算符
运算符种类算数运算符、比较运算符、逻辑运算符、赋值运算符
>>> a = 3
>>> b = 4
>>> a>b and a==3
False
>>> a<b and a==3
True
>>> a<b or a!=3
True
>>> a>b or a==3
True
>>> not a==3
False
>>>
4.6流程控制
4.6.1单分支
if 条件成立:
执行代码
# _*_coding:utf-8_*_
"""
输入姓名，性别和年龄，
如果是女生且年龄小于28，输出我喜欢年轻女孩
"""
name = input("input your name:")
sex = input("input your sex(boy|BOY/girl|GIRL):")
#input()读入的age是字符串，要转换为int才能与28做大小比较
age = int(input("input your age:"))
if sex.lower() == "girl" and age < 28:
print(name+" i like young girl")
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):GIRL
input your age:26
vita i like young girl
4.6.2双分支
if 条件:
条件满足，执行代码
else:
条件不满足，执行代码
# _*_coding:utf-8_*_
"""
输入姓名，性别和年龄，
如果是女生
年龄小于28，输出我喜欢年轻女孩,
年龄不小于28，输出年龄比我大也可以
如果不是女生
输出我不喜欢男生
"""
name = input("input your name:")
sex = input("input your sex(boy|BOY/girl|GIRL):")
#input()读入的age是字符串，要转换为int才能与28做大小比较
age = int(input("input your age:"))
if sex.lower() == "girl" :
if age < 28:
print(name+" i like young girl")
else:
print("the age is greater than me is also ok!")
else:
print("i do not like boy")
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):girl
input your age:12
vita i like young girl
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):girl
input your age:28
the age is greater than me is also ok!
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):boy
input your age:23
i do not like boy
4.6.3多分支
if 条件:
满足条件执行代码
elif 条件:
上面条件不满足，执行这里
elif 条件:
上面条件不满足，执行这里
else:
所有条件都不满足，执行这里
# _*_coding:utf-8_*_
"""
输入姓名，性别和年龄，
如果是女生
年龄小于28，输出我喜欢年轻女孩,
年龄不小于28，输出年龄比我大也可以
如果不是女生
输出我不喜欢男生
"""
name = input("input your name:")
sex = input("input your sex(boy|BOY/girl|GIRL):")
#input()读入的age是字符串，要转换为int才能与28做大小比较
age = int(input("input your age:"))
if sex.lower() == "girl" :
if age < 28:
print(name+" i like young girl")
else:
print("the age is greater than me is also ok!")
elif sex.lower() == "boy":
print("i do not like boy")
else:
print("your input is not manual human")
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/singleif.py
input your name:vita
input your sex(boy|BOY/girl|GIRL):w
input your age:23
your input is not manual human
4.6.4while
while 条件:
执行代码
"""
只打印1-10的偶数
"""
count = 0
while count < 10:
if count%2 == 0:
print(count)
count = count + 1
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
2
4
6
8
"""
打印1-10，第五次不打印，6-8打印值的平方
"""
count = 0
while count <= 10:
if count == 5:
pass
elif count>=6 and count<=8:
print(count*count)
else:
print(count)
count = count + 1
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
2
3
4
36
49
64
9
10
4.6.5死循环(dead loop)
只要运行起来，就不再停止,直到把内存耗尽
"""
只打印1-10的偶数
"""
count = 0
while count < 10:
print(count)
# count = count + 1
#注释掉最后一行，程序一直成立，会一直运行
4.6.6循环终止
break:用于完全结束一个循环，跳出循环体执行循环后面的语句 continue:终止本次循环，下次的循环继续
"""
打印1-10，第五次不打印，6-8打印值的平方
"""
count = 0
while count <= 10:
if count == 5:
# 这里一定要记得把count+1,否则count就一直等于5，就死循环了
count = count + 1
continue
elif count>=6 and count<=8:
print(count*count)
else:
print(count)
count = count + 1
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
2
3
4
36
49
64
9
10
"""
打印1-10，第五次不打印，6-8打印值的平方
"""
count = 0
while count <= 10:
if count == 5:
# 这里一定要记得把count+1,否则count就一直等于5，就死循环了
count = count + 1
break
elif count>=6 and count<=8:
print(count*count)
else:
print(count)
count = count + 1
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
2
3
4
4.6.7while...else
只有在Python中有while...else while后面的else指，当while循环正常执行完，中间没有被break中止的话，就会执行else
count = 0
while count <= 3:
if count == 2:
count = count + 1
continue
else:
print(count)
count = count + 1
else:
print("success")
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
3
success
count = 0
while count <= 3:
if count == 2:
count = count + 1
break
else:
print(count)
count = count + 1
else:
print("success")
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py
0
1
本章代码案例：
"""
猜年龄游戏：
允许用户最多猜三次，猜了三次后，询问是都继续玩，如果输入Y，可以继续猜三次，否则退出
"""
age = 23
count = 0
while count < 3:
try:
guess_age = int(input("input the age of you think:"))
except ValueError:
print("you should input one number!")
count = count + 1
continue
if guess_age > 23:
print("the age you input is too big!")
elif guess_age < 23:
print("the age you input is too small!")
else:
print("excellent!you are right!")
break
count = count + 1
while count == 3:
your_choice = input("you only have three chances,would you like to continue(Y|y/N|n):")
if your_choice.lower() == "y":
count = 0
elif your_choice.lower() =="n":
break
else:
print("your input is illegal!input again!")
运行
E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/guessage.py
input the age of you think:2
the age you input is too small!
input the age of you think:45
the age you input is too big!
input the age of you think:33
the age you input is too big!
you only have three chances,would you like to continue(Y|y/N|n):y
input the age of you think:2w
you should input one number!
input the age of you think:24
the age you input is too big!
input the age of you think:55
the age you input is too big!
you only have three chances,would you like to continue(Y|y/N|n):y
input the age of you think:23
excellent!you are right!
Process finished with exit code 0
