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Python开发基础 day5 函数的定义与使用

#coding:utf-8:
# x= # uhello

# print(x.encode(gbk))
# print(b\xc4\xe3)

# y=b\xc4\xe3
# print(y.decode(gbk))

 

 


# x= #unicode.encode(utf-8)

 

y=u
print repr(y)

 


# while True:
# msg=input(>>: )
#
# # print(len(msg))
# # res=len(msg)
# # if res < 5:
# # continue
# # else:break
#
#
# if len(msg) < 5:
# continue
# else:break
#
# with open(a.txt) as f:
# for i in f.readlines():
# print(i,end=‘‘)

# with open(a.txt) as f:
# for i in f:
# print(i,end=‘‘)


# with open(a.txt) as f:
# print(f.readline(),end=‘‘)
# print(f.readline(),end=‘‘)
# print(f.readline(),end=‘‘)
# print(f.readline(),end=‘‘)
# print(f.readline(), end=‘‘)
# print(f.readline(), end=‘‘)


# with open(a.txt,r,encoding=utf-8) as f:
# print(len(f.read()))


# with open(a.txt,rb) as f:
# file_size=len(f.read())


# import os
# print(os.path.getsize(a.txt))

 




函数参数的使用:



# def foo(x): # print(x) # # # foo(
1) # foo(a) # foo({a:2}) #形参与实参: # def foo(x,y): #x=1,y=2 # return x+y # # foo(1,2)

 

#===================================part1
#位置参数:按照从左到右的顺序依次定义的参数
def foo(x,y):
print(x)
print(y)
#按位置定义的形参,必须被传值,多一个不行,少一个也不行

# foo(1,2,3)


#按位置定义的实参,与形参一一对应
# foo(2,10)

 

 

 

 

#===================================part2
#关键字参数:实参在定义时,按照key=value形式定义

# def foo(x,y):
# print(x)
# print(y)
#
# # foo(y=10,x=1)
# foo(y=10,x=1) #关键字参数可以不用像位置实参一样与形参一一对应,指名道姓地传值

 

 

def foo(x,y):
print(x)
print(y)


# foo(1,10)
# foo(x=1,y=10)
# foo(1,y=10)
# foo(y=10,1)
# foo(x=10,1)

# foo(1,x=10,y=20)


# def foo(x,y,z):
# print(x)
# print(y)
# print(z)
# # foo(1,z=20,10)
# foo(1,y=2,z=10)

 

#注意的问题一:位置实参必须在关键字实参的前面
#注意的问题二:实参的形式既可以用位置实参又可以是关键字实参,但是一个形参不能重复传值

 


#===================================part3
#默认参数:在定义函数阶段,就已经为形参赋值,定义阶段有值,调用阶段可以不用传值

# def func(x,y=10):
# print(x)
# print(y)


# func(1,20)
# func(1)

 

# def func(y=10,x):
# print(x)
# print(y)

 

 

#位置实参
#关键字实参

#位置形参
#默认参数(形参)


#形参的应用:值经常变化的需要定义成位置形参,
# 值大多数情况下都一样,需要定义成默认参数

# def register(name,age,sex=male):
# print(name,age,sex)
#
# register(alex,1000)
# register(wupeiqi,9000)
# register(yuanhao,10000)
# register(王铁蛋,10000,female)

 

 

 

 

#默认参数需要注意的问题一:必须放在位置形参后面
#默认参数需要注意的问题二:默认参数通常要定义成不可变类型
#默认参数需要注意的问题三:默认参数只在定义阶段被赋值一次

# x=10
# def func(name,age=x):
# print(name)
# print(age)
# x=20
#
# func(egon)

 

 

# def func(name,age=10,sex=male,hobby=[play1,play2]):
# print(name)
# print(age)
# print(hobby)
#
# func(egon)

 

#===================================part4
#可变长参数:可变长指的是实参的个数不固定
#按位置定义的可变长度的实参:*
#按关键字定义的可变长度的实参:**

#
# def func(x,y,*args): #x=1,y=2,args=(3,4,5,6)
# print(x,y)
# print(args)
#
# func(1,2,3,4,5,6)

 


# def func(x,y,*args): #args=(3,4,5,6)
# print(x,y)
# print(args)
#
# func(1,2,*(3,4,5,6)) #foo(1,2,3,4,5,6)


# def func(x,y,z):
# print(x,y,z)
#
# # func(1,*(2,3)) #func(1,2,3)
# func(*(2,3)) #func(2,3)

 

#
# def func(x,y=2,z=1):
# print(x,y,z)
#
#
# func(*(a,b,c)) #func(a,b,c)

 

 

 

 

 

# def func(x,y,**kwargs): #x=1,y=2,kwargs={a:1,b:3,z:3}
# print(x,y)
# print(kwargs)
#
# func(1,y=2,z=3,a=1,b=3)

 

 

# def func(x,y,**kwargs): #x=1,y=2,**kwargs=**{a:1,b:3,z:3}
# print(x,y)
# print(kwargs)
#
# func(1,y=2,**{a:1,b:3,z:3}) #func(1,y=2,z=3,b=3,a=1)


# def func(x,y=1,z=1):
# print(x,y,z)
#
# func(**{y:2,x:1,z:3}) #

 


# def wrapper(*args,**kwargs): #可以接受任意形式,任意长度的参数
# print(args)
# print(kwargs)
#
#
# wrapper(1,2,3,3,3,3,3,x=1,y=2,z=3)

 


#
# def index(name,group):
# print(welcome %s to index page,group is: %s %(name,group))
#
# def wrapper(*args,**kwargs): #可以接受任意形式,任意长度的参数
# # print(args) #args=(1,2,3)
# # print(kwargs) #kwargs={x:1,y:2,z:3}
# index(*args,**kwargs) #index(*(1,2,3),**{x:1,y:2,z:3}) #index(1,2,3,z=3,y=2,x=1)
#
# wrapper(name=egon,group=group1)

 

 

 


#命名关键字参数:定义在*后的形参,这类形参,必须被传值,而且要求实参必须是以关键字的形式来传值

# def register(**kwargs):
# print(kwargs)
# if name in kwargs:
# print(kwargs[name])
# if age in kwargs:
# print(kwargs[age])
#
#
# # register(name=egon,age=18)
# register()

 

# def register(*args,name=egon,age):
# print(args)
# print(name)
# print(age)
#
# # register(name=egon,age=18)
# register(1,2,2,3,age=10)

 

#
# def register(name,age,*,group,**kwargs):
# print(name)
# print(age)
# print(kwargs)
#
#
# # register(egon,18)
# register(egon1,18,hobby=paly1,group=group1)


# def func(x,y=1,*args,z,**kwargs):
# print(x)
# print(y)
# print(args)
# print(z)
# print(kwargs)
#
# func(1,2,3,4,5,z=10,a=1,b=2)

 

#
# def func(x,*args,z=1,**kwargs):
# print(x)
# print(args)
# print(z)
# print(kwargs)
#
# func(1,2,3,4,5,a=1,b=2,c=3)

 

 

 


#形参:位置形参,默认参数,*args,命名关键字参数,**kwargs

 

函数的返回值:

 

# y=x**2

 

 

 

# def func(x):
# return x**2
# y=func(10) # 10**2
#
# print(y)

 

 

 

# def foo():
# return None
#
# res=foo()
# print(res)

 


# def foo():
# return {a:1}
#
# res=foo()
# print(res[a])

 

 

 

# def foo():
# return {a:1},1,a,[1,2]
#
# res=foo()
# print(res)

 


‘‘‘
返回值:可以返回任意类型
没有return:None
return value: value
return val1,val2,val3 :(val1,val2,val3)

 


return的效果:只能返回一次值,终止函数的执行
‘‘‘

 


def foo():
return 1
print(=====>)
return 2
return 3
return 4

 

print(foo())

 

 函数的使用原则:

 

#函数的使用必须遵循:先定义后使用的原则

 

#函数的定义,与变量的定义是相似的,如果没有事先定义函数而直接引用
#就相当于在引用一个不存在变量名

 

# print(x) #NameError
# x=1


# func
#
# def func():
# print(hello world)


 


 


# def func():
# print(hello world)
#
# # print(func)
# func()


 


 


# def bar():
# print(from bar)
#
# def foo():
# print(from foo)
# bar()
#
# foo()


 


# #定义阶段
# def foo():
# print(from foo)
# bar()
#
# def bar():
# print(from bar)
#
# #调用阶段
# foo()



#定义阶段:只检测语法,不执行代码
# def func():
# if 1>2
# print(hahahahahahah)



def func(): #语法没问题,逻辑有问题,引用一个不存在的变量名
asdfasdfasdfasdfasdf


 

 

 

函数对象:

#函数是第一类对象: 指的是函数可以被当做数据传递

def func():
print(from func)

#可被引用
# f=func

#可以当做函数的参数
# def func():
# print(from func)
# def foo(x):
# print(x)
# x()
#
# foo(func)

#可以当做函数的返回值
# def foo():
# print(from foo)
# def bar():
# return foo
# f=bar()
# print(f)
# print(foo)

# x=0
# def f1():
# x=1
# def f2():
# # x=2
# print(x)
# return f2
# f=f1()
# # print(f)
# f()

 

#可以当做容器类型的元素
# def select():
# print(select function)
#
# func_dic={
# select:select,
# }
#
# # print(func_dic[select])
# func_dic[select]()

 

 


#
# def select():
# print(select func)
#
# def delete():
# print(delete func)
#
# def change():
# print(change func)
#
# def add():
# print(add func)
#
#
# while 1:
# cmd=input(>>: ).strip()
# if not cmd:continue
# if cmd == select:
# select()
# elif cmd == delete:
# delete()
# elif cmd == change:
# change()
# elif cmd == add:
# add()
# else:
# print(无效的命令)

 

 

 

def select(cmd_l):
filename=cmd_l[-1]
pattern=cmd_l[1]

with open(filename,r,encoding=utf-8) as f:
for line in f:
if pattern in line:
print(line)


def delete():
print(delete func)

def change():
print(change func)

def add():
print(add func)

def check():
print(check func)


func_dic={
select:select,
delete:delete,
change:change,
add:add,
check:check,
}


while 1:
inp=input(>>: ).strip()
if not inp:continue
cmd_l=inp.split()
# print(cmd_l)
cmd=cmd_l[0]
if cmd in func_dic:
func_dic[cmd](cmd_l)
else:
print(无效的命令)

 

 函数嵌套:

#函数的嵌套调用

#
# def max2(x,y):
# if x > y:
# return x
# else:
# return y
#
# def max4(a,b,c,d):
# res1=max2(a,b) #23
# res2=max2(res1,c) #23
# res3=max2(res2,d) #31
# return res3
#
#
# print(max4(11,23,-7,31))

 

#函数的嵌套定义

def f1():
def f2():
def f3():
print(from f3)
print(from f2)
f3()
print(from f1)
f2()
# print(f1)
f1()

‘‘‘
from f1
from f2
from f3

‘‘‘

 

 

名称空间与作用域:

#名字空间:存放名字与值的绑定关系


#名称空间分为三种


#内置名称空间:python解释器自带的名字,python解释器启动就会生成

 

#全局名称空间:文件级别定义的名字都会存放与全局名称空间,执行python文件时会产生

# x=1
# def func():
# pass
#
# class Foo:
# pass
#
# import os
#
# if 1 > 2 :
# y=3

#局部名称空间:定义在函数内部的名字,局部名称空间只有在调用函数时才会生效,函数调用结束则失效
# def func(x,y): #x=1,y=2
# z=3

# func(1,2)

 

#三者的加载顺序:内置名称空间->全局名称空间->局部名称空间

#取值:局部名称空间->全局名称空间->内置名称空间

 

# # max=10
# def func(): #x=1
# # max=20
# print(max)
#
#
# func()

 

# max=10
#
# def func(): #x=1
# max=20
# # print(max)
# func()
#
#
# print(max)
#


# # x=0
# def f1():
# # x=1
# def f2():
# # x=2
# def f3():
# # x=3
# print(x)
# f3()
# f2()
#
# f1()

 

#作用域:作用范围
#全局作用域:内置名称空间与全局名称空间的名字属于全局范围,
# 在整个文件的任意位置都能被引用,全局有效
#局部作用域:局部名称空间的名字属于局部范围,
#只在函数内部可以被引用,局部有效

 

# x=1
# def foo():
# def f2():
# print(x)
# f2()
# def bar():
# print(x)
#
# foo()
# bar()


# def f1():
# x=1
# def f2(): #f2=value
# # x=2
# print(x)
# f2()
# f1()


x=1
def func():
x=2
def f1():pass
# print(dir(globals()[__builtins__])) #全局作用域name
# print(locals()) #局部作用域name

func()

print(globals() is locals())


#局部作用域----->全局作用域

 

Python开发基础 day5 函数的定义与使用