Python基础小知识

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注：一个区分大小写的语言

数据类型：

• 整数 #a=2
• 浮点数 #a=3.23和b=23.8E
• 复数 #(-5+4j)

字符串

• 单引号 #'this is a demo1'
• 双引号 #"this is a demo2"
• 三引号 #'''this is a demo3,"what's your name？"'''，可以在三引号中自由的使用单引号和双引号

转义字符

\n #换行

\\ #转义字符

format方法

`name="ZhangSan"`
`age=18`
`print('{0} is {1} years old'.format(name,age))`

变量

Python声明一个变量不需要规定其变量的数据类型，会自动识别
Python变量由字母、下划线或者数字组成 #数字不能该开头

变量和常量的区别：见demo
i = 5 i = i+1 s = "hello world"

运算符和表达式

• 运算符的优先级 #可以使用括号利于阅读且查看优先级
• 相同优先级的运算符一般是按照从左到右的顺序计算的 #2+3+4

控制流

• if语句

# -*- coding：utf-8 -*-
#循环的输入：
Number = 23
running = True
while running:
    Input_Number = int(input('Please enter a number:'))
    if Input_Number == Number:
        print('You got it ,good job!!!')
        running = False
    elif Input_Number >Number:
        print('this number is higher')
    else:
        print("this number is lower")
        break;
        print("done")    
else:
    print("the while loop is over.")
print("Done")

• for循环

for i in range(1,6):
    print(i)

• while循环
• break语句
• continue语句

函数

• 基础格式

def sayhello():
      print("hello!!!")
sayhello()

• 函数的参数

# -*- coding：utf-8 -*-
#定义获取最大值函数
def getMaxSize(a,b):
    if a >b:
        print("the large size is ",a)
    elif a == b:
        print(a,"is equal to",b)
    else:
        print("the large size is ",b)
getMaxSize(10,5)

• 局部变量

# -*- coding：utf-8 -*-
x = 20
def func(x):
    print("x is ",x)
    x=2  #此处的X是局部变量只在整个函数生效，在此函数之外则就无效了
    print("x is ",x)
func(x)
print("x is still",x)

• 全局语句

# -*- coding：utf-8 -*-
gcount = 0
def global_test():
    print (gcount) 
def global_counter():
    global gcount
    gcount +=1
    return gcount    
def global_counter_test():
    print(global_counter())
    print(global_counter())
    print(global_counter())
global_counter_test()
输出结果：1 2 3

• 非全局语句

# -*- coding：utf-8 -*-
def make_counter():
    count = 0
    def counter():
        nonlocal count
        count += 1
        return count
    return counter
def make_counter_test():
    mc = make_counter()
    print(mc())
    print(mc())
    print(mc())
make_counter_test()

• 默认参数值

# -*- coding：utf-8 -*-
def say(message,time=1):
    print(message*time)
say("hello\n",5)

• 关键参数

# -*- coding：utf-8 -*-
def func(a,b=5,c=6):
    print("a is",a,"\n", "b is",b,"\n", "c is",c,"\n")
func(5)
func(10,5,30)
func(5,c=2)

• VarArgs参数
  “*****”参数名：代表这是一个列表
  “****”参数名：代表这是一个字典

# -*- coding：utf-8 -*-
def total(inttial=5, *numbers,**keywords):
    count = inttial
    for number in numbers:
        count +=number
        print("number:",number)
        print("count:",count)
    for key in keywords:
        count +=keywords[key]
        print("key:",key)
        print("count:",count)
    return count
print(total(10,1,2,3,vegt=50,frunits=100))
输出结果：
number: 1
count: 11
number: 2
count: 13
number: 3
count: 16
key: vegt
count: 66
key: frunit
count: 166

• keyword-only参数
  在带*号的参数后面声明参数，在输出函数时赋值或者给定一个默认参数值

# -*- coding：utf-8 -*-
def total(inttial=5, *numbers,vegetables):
    count = inttial
    for number in numbers:
        count +=number
    count += vegetables
    return "the count is :",count
print(total(10,1,2,3,vegetables=50))
print(total(10,1,2,3,))
输出结果：
('the count is :', 66)
Traceback (most recent call last):
  File "C:\Users\yuanyuan_cheng\Desktop\python-demo.py", line 10, in <module>
    print(total(10,1,2,3,))
TypeError: total() missing 1 required keyword-only argument: 'vegetables'

要是给vegetables=5，就不会出现上面的TypeError
正确输出：('the count is :', 66) ('the count is :', 21)

• return语句

def maxsize(x,y):
    if x>y:
        return "the large value is ",x
        print(x)
    else:
        return "the large value is ",y
        print(y)
print(maxsize(50,2))

• DocString

# -*- coding：utf-8 -*-
def printMax(x,y):
    '''
    the docmentstring 
    '''
    x = int(x)
    y = int(y)
    if x>y:
        print(x,'is maximum')
    else:
        print(y,'is maximum')
printMax(3,5)
print(printMax.__doc__) #打印出信息
help(printMax) #打印出函数下的信息
输出结果：
5 is maximum
    the docmentstring 
Help on function printMax in module __main__:
printMax(x, y)
    the docmentstring

并不是早起有多困难，而是早起后干什么，这件事你没考虑好。