python装饰器property和setter用法

def hi(name="yasoob"):
return "hi "   name
print(hi())
# output: 'hi yasoob'
# 我们甚至可以将一个函数赋值给一个变量，比如
greet = hi
# 我们这里没有在使用小括号，因为我们并不是在调用hi函数
# 而是在将它放在greet变量里头。我们尝试运行下这个
print(greet())
# output: 'hi yasoob'
# 如果我们删掉旧的hi函数，看看会发生什么！
del hi
print(hi())
#outputs: NameError
print(greet())
#outputs: 'hi yasoob'

def hi(name="yasoob"):
print("now you are inside the hi() function")

def greet():
return "now you are in the greet() function"

def welcome():
return "now you are in the welcome() function"

print(greet())
print(welcome())
print("now you are back in the hi() function")

hi()
#output:now you are inside the hi() function
# now you are in the greet() function
# now you are in the welcome() function
# now you are back in the hi() function

# 上面展示了无论何时你调用hi(), greet()和welcome()将会同时被调用。
# 然后greet()和welcome()函数在hi()函数之外是不能访问的，比如：
greet()
#outputs: NameError: name 'greet' is not defined

def hi(name="yasoob"):
def greet():
return "now you are in the greet() function"
def welcome():
return "now you are in the welcome() function"
if name == "yasoob":
return greet #这里！！
else:
return welcome
a = hi()
print(a)
#outputs: <function greet at 0x7f2143c01500>
#上面清晰地展示了`a`现在指向到hi()函数中的greet()函数
#现在试试这个
print(a())
#outputs: now you are in the greet() function

def hi():
return "hi yasoob!"
def doSomethingBeforeHi(func):
print("I am doing some boring work before executing hi()")
print(func())
doSomethingBeforeHi(hi)
#outputs:I am doing some boring work before executing hi()
# hi yasoob!

def a_new_decorator(a_func):
def wrapTheFunction():
print("I am doing some boring work before executing a_func()")
a_func()
print("I am doing some boring work after executing a_func()")
return wrapTheFunction
@a_new_decorator
def a_function_requiring_decoration():
"""Hey you! Decorate me!"""
print("I am the function which needs some decoration to "
"remove my foul smell")

a_function_requiring_decoration()
#outputs: I am doing some boring work before executing a_func()
# I am the function which needs some decoration to remove my foul smell
# I am doing some boring work after executing a_func()
#the @a_new_decorator is just a short way of saying:
a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)

def a_new_decorator(a_func):
def wrapTheFunction():
print("I am doing some boring work before executing a_func()")
a_func()
print("I am doing some boring work after executing a_func()")
return wrapTheFunction

def a_function_requiring_decoration():
print("I am the function which needs some decoration to remove my foul smell")

a_function_requiring_decoration()
#outputs: "I am the function which needs some decoration to remove my foul smell"
a_function_requiring_decoration = a_new_decorator(a_function_requiring_decoration)
#now a_function_requiring_decoration is wrapped by wrapTheFunction()
a_function_requiring_decoration()
#outputs:I am doing some boring work before executing a_func()
# I am the function which needs some decoration to remove my foul smell
# I am doing some boring work after executing a_func()

print(a_function_requiring_decoration.__name__)
# Output: wrapTheFunction

from functools import wraps
def a_new_decorator(a_func):
@wraps(a_func)
def wrapTheFunction():
print("I am doing some boring work before executing a_func()")
a_func()
print("I am doing some boring work after executing a_func()")
return wrapTheFunction
@a_new_decorator
def a_function_requiring_decoration():
"""Hey yo! Decorate me!"""
print("I am the function which needs some decoration to "
"remove my foul smell")
print(a_function_requiring_decoration.__name__)
# Output: a_function_requiring_decoration

class Timer:
def __init__(self, value = 0.0):
self._time = value
self._unit = 's'
# 使用装饰器的时候，需要注意：
# 1. 装饰器名，函数名需要一直
# 2. property需要先声明，再写setter，顺序不能倒过来
@property
def time(self):
return str(self._time)   ' '   self._unit
@time.setter
def time(self, value):
if(value < 0):
raise ValueError('Time cannot be negetive.')
self._time = value
t = Timer()
t.time = 1.0
print(t.time)