变量
变量定义
# 动态语言变量定义时不需要指明变量的数据类型
# 字符串类型变量可以使用""或''，""和''在Python中没有区别，不加""或''的字符串系统默认为变量名
name = "young"
age = 25
print("My name is", name, "...I'm", age, "years old!")
输出结果如下：
My name is young ...I'm 25 years old!Python中没有常量的概念，如果需要表示某一固定不变的量，例如数学中的π，一般习惯将变量名全大写表示：
PIE = 3.1415926当变量被定义时，内存中会开辟一块区域存放该变量的值，同时变量名指向存放该值的区域
name_1 = "young"
name_2 = name_1 # name_2通过name_1找到内存中存放字符串"young"的地址，并直接指向
print("name_1 = ", name_1, "name_2 = ", name_2)
name_1 = "old" # name_1改为指向内存中存放字符串"old"的地址，而name_2指向不变
print("name_1 = ", name_1, "name_2 = ", name_2)
输出结果如下：
name_1 = young name_2 = young
name_1 = old name_2 = young代码注释
被注释部分在代码执行时会被系统略过
- 单行注释
使用#进行单行注释
# print("My name is", name, "...I'm", age, "years old!")- 多行注释
使用'''注释内容'''或者"""注释内容"""进行多行注释
"""
print("Please call me", name_1, "......say again", name_2)
name_1 = "yang sir"
print("Please call me", name_2, "or", name_1)
"""
# 或
'''
print("Please call me", name_1, "......say again", name_2)
name_1 = "yang sir"
print("Please call me", name_2, "or", name_1)
'''字符编码
- ASCII码
支持英语和其他西欧语言，用 8 位（1个字节）来表示某一字符的编码，ASCII码最多只能表示2**8 = 256-1=255 个字符
- GB2312
相比于ASCII码增加了中文字符的编码，使用16位（2个字节）来表示某一字符的编码，支持中文
- GBK1.0
相比于GB2312增加了更多中文字符的编码，用16位（2个字节）来表示某一字符的编码
- GB18030
相比于GBK1.0增加了更多中文字符以及其他少数名族语言的编码，用16位（2个字节）来表示某一字符的编码
从ASCII、GB2312、GBK 到GB18030，这些编码方法是向下兼容的，即同一个字符在这些方案中总是有相同的编码
- Unicode
世界统一码，为各个不同国家的语言字符设定了统一并且唯一的二进制编码，规定所有的字符和符号最少由 16 位（2个字节）来表示
- UTF-8
UTF-8是对Unicode编码的压缩和优化，他不再使用最少使用2个字节，而是将所有的字符和符号进行分类：ascii码中的内容用1个字节保存、欧洲的字符用2个字节保存，东亚的字符用3个字节保存...
Python2默认字符编码是ASCII码，不支持中文，Python3默认支持中文，如果要让Python2支持中文，需要在代码文件首行中加入以下内容：
# _*_ coding:utf-8 _*_
# 或
# -*- coding:utf-8 -*-如果使用PyCharm作为编译环境，无论是Python2还是Python3，都建议做如下编码设置：
用户输入
name = input("Please input your name :")
输出结果如下：
Please input your name : # 在此处输入赋予变量name的值并键入回车Python2和Python3的区别
# Python2中raw_input()功能和Python3中input()功能相同
name = raw_input("please input your name:")
# Python2中的input()不推荐使用
name = input("Please input your name:")
输出结果如下：
Please input your name:young
# 输入时如果不带"",系统会将输入的内容当作变量名处理
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<string>", line 1, in <module>
NameError: name 'young' is not defined
name = input("Please input your name:")
Please input your name:"young"格式化输出
多行格式化输出
多行注释还具备多行格式化输出的功能
# 跨越多行的字符串打印
hello = '''
Hello Word!
Hello Python!
'''
print(hello)
输出结果如下：
Hello Word!
Hello Python!# 用户输入(经用户输入的变量默认类型为字符串)
name = input("name :")
age = int(input("age :")) # 如果需要检验输入的有效性，建议强制类型转换(str to int)
job = input("job :")
salary = int(input("salary:")) # 如果需要检验输入的有效性，建议强制类型转换(str to int)
# 打印变量的类型
print("name type is", type(name))
print("age type is", type(age))
print("job type is", type(job))
print("salary type is", type(salary))
# 格式化打印
# 方式1：拼接字符串（需要开辟多块内存保存多个字符串变量，效率低，不推荐使用）,参与字符串拼接的变量类型只能是字符串
info_1 = '''
**********Info of ''' + name + '''**********
name : ''' + name + '''
age : ''' + str(age) + '''
job : ''' + job + '''
salary: ''' + str(salary)
print(info_1)
# 方式2: %s表示输入的数据类型为字符出串，%d可暂时理解为数字
info_2 = '''
**********Info of %s**********
name : %s
age : %d
job : %s
salary: %d
''' % (name, name, age, job, salary)
print(info_2)
# 方式3: 官方推荐格式化输出使用这种方式，{}中的内容不一定要是变量名,{}中变量前后不能有空格
info_3 = '''
**********Info of {_name}**********
name : {_name}
age : {_age}
job : {_job}
salary: {_salary}
'''.format(_name=name,
_age=age,
_job=job,
_salary=salary)
print(info_3)
# 方式4:
info_4 = '''
**********Info of {0}**********
name : {0}
age : {1}
job : {2}
salary: {3}
'''.format(name, age, job, salary)
print(info_4)
输出结果如下：
name :young
age :25
job :IT
salary:50000
name type is <class 'str'>
age type is <class 'int'>
job type is <class 'str'>
salary type is <class 'int'>
**********Info of young**********
name : young
age : 25
job : IT
salary: 50000
**********Info of young**********
name : young
age : 25
job : IT
salary: 50000
**********Info of young**********
name : young
age : 25
job : IT
salary: 50000
**********Info of young**********
name : young
age : 25
job : IT
salary: 50000单行格式化输出
# 与多行格式化输出相同
money = 5000000
print("I want to earn " + str(money) + " dollars one day.")
print("I want to earn %d dollars one day." % money)
print("I want to earn {_money} dollars one day.".format(_money=money))
print("I want to earn {0} dollars one day.".format(money))
输出结果如下：
I want to earn 5000000 dollars one day.
I want to earn 5000000 dollars one day.
I want to earn 5000000 dollars one day.
I want to earn 5000000 dollars one day.Python2和Python3区别
name = "young"
age = 25
# Python2中print无()
print "I'm {_name},I have {_age} years old.".format(_name=name, _age=age)
输出结果如下：
I'm young,I have 25 years old.判断语句
可根据需求组合if，if...else，if...elif...elif...else等逻辑判断语句
# 导入Python标准库中的getpass模块
import getpass
username = "young"
password = "123456"
_username = input("Please input your username:")
# getpass输入时不显示任何输入的字符，input（）输入时明文显示输入的字符，
# getpass在PyCharm中运行会卡住，需要到CMD中利用命令运行Python文件
_password = getpass.getpass("Please input your password:")
# Python使用强制缩进来区分不同级别的语句，位于*的语句必须顶格写，不然会出现"IndentationError"缩进错误
# =表示赋值，==表示判断是否相等
if _username == username and _password == password:
print("Welcome {login_name} login !" .format(login_name=username))
else:
print("Invalid username or password !")循环语句
while循环
# 猜年龄，只允许猜3次
age_of_mine = 25
count = 0
while True:
# 只允许循环猜3次
if count >= 3:
# 直接跳出停止循环
count = 0
break
# 做大小关系比较需转换成数字
age = int(input("Please guess my age:"))
if age == age_of_mine:
print("Yes,you got it !")
count = 0
break
elif age > age_of_mine:
print("Please think smaller !")
else:
print("Please think bigger !")
# 每循环一次count计数加1，也可写为count = count + 1
count += 1
# 以上程序优化
while count < 3:
age = int(input("Please guess my age:"))
if age == age_of_mine:
print("Yes,you got it !")
break
elif age > age_of_mine:
print("Please think smaller !")
else:
print("Please think bigger !")
count += 1
# 当while循环每次开始时，while中的条件不成立时执行
else:
print("you have tried too many times...fuck off!")
输出结果如下：
Please guess my age:22
Please think bigger !
Please guess my age:20
Please think bigger !
Please guess my age:26
Please think smaller !
you have tried too many times...fuck off!
Please guess my age:22
Please think bigger !
Please guess my age:20
Please think bigger !
Please guess my age:26
Please think smaller !
you have tried too many times...fuck off!# 猜过3次后，询问是否继续，是则继续，否则停止
age_of_mine = 25
count = 0
while count < 3:
age = int(input("Please guess my age:"))
if age == age_of_mine:
print("Yes,you got it !")
break
elif age > age_of_mine:
print("Please think smaller !")
else:
print("Please think bigger !")
count += 1
if count == 3:
continue_confirm = input("Do you want to keep guessing?(yes/no)")
if continue_confirm != "no":
count = 0
else:
print("Game Over!")
输出结果如下：
Please guess my age:22
Please think bigger !
Please guess my age:26
Please think smaller !
Please guess my age:20
Please think bigger !
Do you want to keep guessing?(yes/no)no
Game Over!
*****************************************
Do you want to keep guessing?(yes/no)yes
Please guess my age:for循环
# 循环10次，0-9
for a in range(10):
print("a =：", a)
# range(起始[默认0]，循环次数，步长[默认1])
for b in range(0, 10, 2):
print("b =：", b)
age_of_mine = 25
for i in range(3):
age = int(input("Please guess my age:"))
if age == age_of_mine:
print("Yes,you got it !")
break
elif age > age_of_mine:
print("Please think smaller !")
else:
print("Please think bigger !")
# 当for循环每次开始时，i的范围不在rang()规定的范围内执行
else:
print("You have tried too many times...fuck off!")break和continue
for i in range(10):
print("loop times: ", i+1)
if i < 3:
print("I have been printed: i =", i)
else:
# continue表示直接跳出本次循环，开始下一次循环
continue
# i>=3时不会被执行，程序经continue后直接开启下一次循环，共循环10次
print("Program didn't skip me!")
输出结果如下：
loop times: 1
I have been printed: i = 0
Program didn't skip me!
loop times: 2
I have been printed: i = 1
Program didn't skip me!
loop times: 3
I have been printed: i = 2
Program didn't skip me!
loop times: 4
loop times: 5
loop times: 6
loop times: 7
loop times: 8
loop times: 9
loop times: 10for a in range(10):
print("loop times: ", a+1)
if a < 3:
print("I have been printed: a =", a)
else:
# break表示直接结束整个循环程序
break
# i=3时程序经break后结束整个循环，共循环3次
print("Program didn't skip me!")
输出结果如下：
loop times: 1
I have been printed: a = 0
Program didn't skip me!
loop times: 2
I have been printed: a = 1
Program didn't skip me!
loop times: 3
I have been printed: a = 2
Program didn't skip me!
loop times: 4for a in range(5):
print("***********:a =", a)
for b in range(5):
if b > 3:
# break只结束当前所在的整个循环程序
break
print("b =", b)
输出结果如下：
***********:a = 0
b = 0
b = 1
b = 2
b = 3
***********:a = 1
b = 0
b = 1
b = 2
b = 3
***********:a = 2
b = 0
b = 1
b = 2
b = 3
***********:a = 3
b = 0
b = 1
b = 2
b = 3
***********:a = 4
b = 0
b = 1
b = 2
b = 3