Python functional Programming--decorators

1.1   Decorative Device

A function object can be assigned to a variable, so the function can also be called by a variable.

>>> def now ():

.. print (' 2016 ')

...

>>> Now ()

2016

>>> F = Now--The function object assigns a value to the variable

>>> f ()-- call

2016

of the Function object __name__ , can get the name of the function

>>> now.__name__

' Now '

>>> f.__name__

' Now '

Suppose we want to enhance the function of the now () function, for example, to automatically print the log before and after a function call, but do not want to modify the definition of the now () function, a way to dynamically add functionality during the run of the code, called an "adorner" ( Decorator).

Decorator is a higher-order function that returns a function . Define a decorator as follows

>>> def log (func):

... def wrapper (*args, **kw):-- the previous variable parameter and keyword Parameters section has been explained,= can pass any parameter

... print (' Call%s (): '% func.__name__)

... return func (*args, **kw)

... return Wrapper

...

>>> @log-- equivalent to executing now = log (now), redefining the now function.

... def now ():

.. print (' 2016 ')

...

>>> Now ()

Call Now ():

2016

#################################################################

>>> def log2 (func):

... def wrapper (*args, **kw):

... print (' Begin call ')-- execute before calling

... res = func (*args, **kw)

... print (' End call ')-- execution after invocation

... return Res

... return Wrapper

>>> @log2

... def PR ():

.. print (' 2016 ')

...

>>>

>>> PR ()

Begin Call

2016

End Call

##################################################################

>>> def log (text):-- custom text content

... def decorator (func):

... def wrapper (*args, **kw):

... print ('%s%s (): '% (text,func.__name__))

... return func (*args, **kw)

... return Wrapper

... return Decorator

...

>>>

>>>

>>>

>>> @log (' execute ')-- equivalent to execute now=log (' Execute ') (now)

... def now ():

.. print (' 2016 ')

...

>>> Now ()

Execute Now ():

2016

>>> now.__name__

' Wrapper '-- returns the function name, but wrapper

##################################################################

>>> Importfunctools

>>>

>>> def log (func):

... @functools. Wraps (func)

... def wrapper (*args, **kw):

... print (' Call%s (): '% func.__name__)

... return func (*args, **kw)

... return Wrapper

...

>>>

>>>

>>> @log

... def now ():

.. print (' 2 ')

...

>>> now

<function now at 0x2ab1090d9e18>

>>> Now ()

Call Now ():

2

>>> now.__name__

' Now '

##################################################################

>>> Importfunctools

>>> def log (text):

... def decorator (func):

... @functools. Wraps (func)

... def wrapper (*args, **kw):

... print ('%s%s (): '% (text,func.__name__))

... return func (*args, **kw)

... return Wrapper

... return Decorator

...

>>> @log (' Run ')

... def now ():

.. print (' 2016 ')

...

>>> Now ()

Run Now ():

2016

>>> now.__name__

' Now '

just remember to add @functools. Wraps (func) in front of the definition wrapper () .

This article is from the "90SirDB" blog, be sure to keep this source http://90sirdb.blog.51cto.com/8713279/1820989

Python functional Programming--decorators