Python学习笔记——day1

#Python day1

标签： python

[TOC]
##1.Hellow World程序
###1）Hellow World
在linux里创建一个叫hellow.py的文件。

文件内容：
#!/usr/bin/env python
print("Hellow World！")
在linux中需要指定解释器#!/usr/bin/env python
意思是到整个linux系统中找名为python的环境变量。

给予文件执行权限，使用./hellow.py执行文件。

输出结果：
Hellow World！

##2.变量
###1)什么是变量？

变量用于存储在计算机程序中引用和操作的信息。它们还提供了一种用描述性名称标记数据的方法，这样我们的程序就能更清晰地被读者和我们自己理解。将变量看作保存信息的容器是很有帮助的。它们的唯一目的是在内存中标记和存储数据。然后可以在整个程序中使用这些数据。

###变量定义的规则：

变量定义的规则
- 变量名只能是字母、数字或下划线的任意组合
- 变量名的第一个字符不能是数字
- 写的变量名要有含义，否则自己和别人都看不懂
- 变量名最好不要是中文或拼音，多个单词用下划线分隔
- 以下关键字不能声明为变量名
```
['and', 'as', 'assert', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 'exec', 'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 'not', 'or', 'pass', 'print', 'raise', 'return', 'try', 'while', 'with', 'yield']
```

###什么是常量？

常量：不会变的量，比如π是3.14...

python定义常量，变量名要大写比如：PIE = "em"

###2)变量的赋值：

name = "byh"
name2 = name

print(name,"-----",name2)

name = "em"
print(name,"-----",name2)

print:输出字符

输出结果：
byh ----- byh
em ----- byh

Process finished with exit code 0


>###为什么第二个name2输出的是 byh,而不是em呢？
* 因为：
    - name2只是通过name找到byh的，name2≠name
    - name = em只是从新定义了name，name2还是通过第一个name变量找到byh

<br/>
>注释

当行注释|“#”标识当行
---------|---------------
多行注释|''' 或 """  都表示多行注释

<br>
<br>

---

<br>
<br>

##3.用户输入
###1)简单用户输入

username = input("username:")
password = input("password:")

print("Hellow",username)


>输入密码时，如果要密码不可见，需要使用`getpass`模块中的getpass方法：

import getpass

username = input("username:")
password = getpass.getpass("password:")

print("Hellow",username)

<br />

###2)用户输入，输出调用变量

>方法一：

name = input("name:")
age = int(input("age:"))
print(type(age))
job = input("job:")
salary = int(input("salary:"))
print(type(salary))

info = '''
-------- info of %s--------
Name:%s
Age:%d
Job:%s
Salary:%d
''' %(name,name,age,job,salary)

print(info)


%s|代表string字符串
---|---
%d|代表整数
%f|代表有小数点的数
int()|强制转换类型为integer
str()|强制转换类型为string
print(type(salary))|输出字符串类型

>输出结果：

name:em
age:19
<class 'int'>
job:IT
salary:1234567
<class 'int'>

-------- info of em--------
Name:em
Age:19
Job:IT
Salary:1234567

Process finished with exit code 0

<br/>
>方法二：

#Author:byh
name = input("name:")
age = int(input("age:"))
print(type(age))
job = input("job:")
salary = int(input("salary:"))
print(type(salary))

info = '''
-------- info of {_name}--------
Name:{_name}
Age:{_age}
Job:{_job}
Salary:{_salary}
''' .format(_name=name,
_age=age,
_job=job,
_salary=salary)

print(info)


>输出结果：

name:em
age:19
<class 'int'>
job:IT
salary:1234567
<class 'int'>

-------- info of em--------
Name:em
Age:19
Job:IT
Salary:1234567

Process finished with exit code 0


<br/>

>方法三：

#Author:byh
name = input("name:")
age = int(input("age:"))
print(type(age))
job = input("job:")
salary = int(input("salary:"))
print(type(salary))

info = '''
-------- info of {0}--------
Name:{0}
Age:{1}
Job:{2}
Salary:{0}
''' .format(name,name,age,job,salary)

print(info)


>输出结果：

name:em
age:19
<class 'int'>
job:IT
salary:1234567
<class 'int'>

-------- info of em--------
Name:em
Age:em
Job:19
Salary:em

Process finished with exit code 0


<br/>
<br/>

---

<br/>
<br/>

##4.表达式if ... else
###场景一 : 用户登陆验证

_username = "byh"
_password = "123"
username = input("username:")
password = input("password:")

if _username == username and _password == password:
print("Welcome user {name} login...".format(name=_username))
else:
print("Invaild username or password!")

elif|如果这个条件不成立，那么下个条件是否成立呢
---|---

>输出结果：

#验证成功输出
username:byh
password:123
Welcome user byh login...

#验证失败输出
username:em
password:123
Invaild username or password!

###场景二 : 猜年龄游戏

_myage = 22
myage = int(input("myage:"))

if myage == _myage:
print("yes, it is")
elif myage > _myage:
print("should be smaller..")
else:
print("should be more big..")


>输出结果

myage:17
should be more big..

myage:23
should be smaller..

myage:22
yes, it is

<br/>
<br/>

---

<br/>
<br/>

##5.while循环
###1)简单while循环

count = 0
while True:
print("count:",count)
count +=1
if count == 1000:
break

>当这个条件成立时：True（永远为真），如果没有定义 `break`条件结束循环，则会一会循环下去。

<br/>

###2)while循环猜年龄游戏

#实现用户可以不断的猜年龄，最多3次机会，继续按如意键，退出按“n”

_myage = 22
count = 0

while count < 3:
myage = int(input("myage:"))
if myage == _myage:
print("yes it is.")
break
elif myage > _myage:
print("should be smaller...")
else:
print("should be more big...")
count +=1
if count == 3:
countine_config = input("do you want to keep gussing?")
if countine_config !="n":
count = 0


break|结束当前整个循序
---|---
continue|跳出本次循环，进入下次循环
count|添加计数

>输出结果：

#继续猜：
myage:1
should be more big...
myage:2
should be more big...
myage:3
should be more big...
do you want to keep gussing?
myage:12
should be more big...
myage:22
yes it is.

Process finished with exit code 0

#不猜退出：
myage:1
should be more big...
myage:2
should be more big...
myage:3
should be more big...
do you want to keep gussing?n

Process finished with exit code 0

<br/>
<br/>

---

<br/>
<br/>

##6.for循环
###1）简单for循环

#0,10是范围，1是增数
for i in range(0,10,1):
print("number",i)

>输出结果：

number 0
number 1
number 2
number 3
number 4
number 5
number 6
number 7
number 8
number 9

Process finished with exit code 0


###2)for循环猜年龄游戏

#用户最多猜3次
_myage = 22

for i in range(3):
myage = int(input("myage:"))
if myage == _myage:
print("yes it is.")
break
elif myage > _myage:
print("should be smaller..")
else:
print("should be more big..")

else:
print("you have tried too many times")


>输出结果：

myage:1
should be more big..
myage:2
should be more big..
myage:3
should be more big..
you have tried too many times

Process finished with exit code 0

Python学习笔记——day1

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