Python基础小知识
2017-03-24 本文已影响86人
Tester_Jingel
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。
