python - Comment faire des décorateurs de fonction et les chaîner ensemble

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meilleur 5 Réponses python - Comment faire des décorateurs de fonction et les chaîner ensemble

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97

def shout(word="yes"):     return word.capitalize()+"!"  print(shout()) # outputs : 'Yes!'  # As an object, you can assign the function to a variable like any other object  scream = shout  # Notice we don't use parentheses: we are not calling the function, # we are putting the function "shout" into the variable "scream". # It means you can then call "shout" from "scream":  print(scream()) # outputs : 'Yes!'  # More than that, it means you can remove the old name 'shout', # and the function will still be accessible from 'scream'  del shout try:     print(shout()) except NameError as e:     print(e)     #outputs: "name 'shout' is not defined"  print(scream()) # outputs: 'Yes!' 
def talk():      # You can define a function on the fly in "talk" ...     def whisper(word="yes"):         return word.lower()+"..."      # ... and use it right away!     print(whisper())  # You call "talk", that defines "whisper" EVERY TIME you call it, then # "whisper" is called in "talk".  talk() # outputs:  # "yes..."  # But "whisper" DOES NOT EXIST outside "talk":  try:     print(whisper()) except NameError as e:     print(e)     #outputs : "name 'whisper' is not defined"*     #Python's functions are objects 
def getTalk(kind="shout"):      # We define functions on the fly     def shout(word="yes"):         return word.capitalize()+"!"      def whisper(word="yes") :         return word.lower()+"..."      # Then we return one of them     if kind == "shout":         # We don't use "()", we are not calling the function,         # we are returning the function object         return shout       else:         return whisper  # How do you use this strange beast?  # Get the function and assign it to a variable talk = getTalk()        # You can see that "talk" is here a function object: print(talk) #outputs : <function shout at 0xb7ea817c>  # The object is the one returned by the function: print(talk()) #outputs : Yes!  # And you can even use it directly if you feel wild: print(getTalk("whisper")()) #outputs : yes... 
def doSomethingBefore(func):      print("I do something before then I call the function you gave me")     print(func())  doSomethingBefore(scream) #outputs:  #I do something before then I call the function you gave me #Yes! 
# A decorator is a function that expects ANOTHER function as parameter def my_shiny_new_decorator(a_function_to_decorate):      # Inside, the decorator defines a function on the fly: the wrapper.     # This function is going to be wrapped around the original function     # so it can execute code before and after it.     def the_wrapper_around_the_original_function():          # Put here the code you want to be executed BEFORE the original function is called         print("Before the function runs")          # Call the function here (using parentheses)         a_function_to_decorate()          # Put here the code you want to be executed AFTER the original function is called         print("After the function runs")      # At this point, "a_function_to_decorate" HAS NEVER BEEN EXECUTED.     # We return the wrapper function we have just created.     # The wrapper contains the function and the code to execute before and after. It’s ready to use!     return the_wrapper_around_the_original_function  # Now imagine you create a function you don't want to ever touch again. def a_stand_alone_function():     print("I am a stand alone function, don't you dare modify me")  a_stand_alone_function()  #outputs: I am a stand alone function, don't you dare modify me  # Well, you can decorate it to extend its behavior. # Just pass it to the decorator, it will wrap it dynamically in  # any code you want and return you a new function ready to be used:  a_stand_alone_function_decorated = my_shiny_new_decorator(a_stand_alone_function) a_stand_alone_function_decorated() #outputs: #Before the function runs #I am a stand alone function, don't you dare modify me #After the function runs 
a_stand_alone_function = my_shiny_new_decorator(a_stand_alone_function) a_stand_alone_function() #outputs: #Before the function runs #I am a stand alone function, don't you dare modify me #After the function runs  # That’s EXACTLY what decorators do! 
@my_shiny_new_decorator def another_stand_alone_function():     print("Leave me alone")  another_stand_alone_function()   #outputs:   #Before the function runs #Leave me alone #After the function runs 
another_stand_alone_function = my_shiny_new_decorator(another_stand_alone_function) 
def bread(func):     def wrapper():         print("</''''''\>")         func()         print("<\______/>")     return wrapper  def ingredients(func):     def wrapper():         print("#tomatoes#")         func()         print("~salad~")     return wrapper  def sandwich(food="--ham--"):     print(food)  sandwich() #outputs: --ham-- sandwich = bread(ingredients(sandwich)) sandwich() #outputs: #</''''''\> # #tomatoes# # --ham-- # ~salad~ #<\______/> 
@bread @ingredients def sandwich(food="--ham--"):     print(food)  sandwich() #outputs: #</''''''\> # #tomatoes# # --ham-- # ~salad~ #<\______/> 
@ingredients @bread def strange_sandwich(food="--ham--"):     print(food)  strange_sandwich() #outputs: ##tomatoes# #</''''''\> # --ham-- #<\______/> # ~salad~ 
# The decorator to make it bold def makebold(fn):     # The new function the decorator returns     def wrapper():         # Insertion of some code before and after         return "<b>" + fn() + "</b>"     return wrapper  # The decorator to make it italic def makeitalic(fn):     # The new function the decorator returns     def wrapper():         # Insertion of some code before and after         return "<i>" + fn() + "</i>"     return wrapper  @makebold @makeitalic def say():     return "hello"  print(say()) #outputs: <b><i>hello</i></b>  # This is the exact equivalent to  def say():     return "hello" say = makebold(makeitalic(say))  print(say()) #outputs: <b><i>hello</i></b> 
# It’s not black magic, you just have to let the wrapper  # pass the argument:  def a_decorator_passing_arguments(function_to_decorate):     def a_wrapper_accepting_arguments(arg1, arg2):         print("I got args! Look: {0}, {1}".format(arg1, arg2))         function_to_decorate(arg1, arg2)     return a_wrapper_accepting_arguments  # Since when you are calling the function returned by the decorator, you are # calling the wrapper, passing arguments to the wrapper will let it pass them to  # the decorated function  @a_decorator_passing_arguments def print_full_name(first_name, last_name):     print("My name is {0} {1}".format(first_name, last_name))      print_full_name("Peter", "Venkman") # outputs: #I got args! Look: Peter Venkman #My name is Peter Venkman 
def method_friendly_decorator(method_to_decorate):     def wrapper(self, lie):         lie = lie - 3 # very friendly, decrease age even more :-)         return method_to_decorate(self, lie)     return wrapper           class Lucy(object):          def __init__(self):         self.age = 32          @method_friendly_decorator     def sayYourAge(self, lie):         print("I am {0}, what did you think?".format(self.age + lie))          l = Lucy() l.sayYourAge(-3) #outputs: I am 26, what did you think? 
def a_decorator_passing_arbitrary_arguments(function_to_decorate):     # The wrapper accepts any arguments     def a_wrapper_accepting_arbitrary_arguments(*args, **kwargs):         print("Do I have args?:")         print(args)         print(kwargs)         # Then you unpack the arguments, here *args, **kwargs         # If you are not familiar with unpacking, check:         # http://www.saltycrane.com/blog/2008/01/how-to-use-args-and-kwargs-in-python/         function_to_decorate(*args, **kwargs)     return a_wrapper_accepting_arbitrary_arguments  @a_decorator_passing_arbitrary_arguments def function_with_no_argument():     print("Python is cool, no argument here.")  function_with_no_argument() #outputs #Do I have args?: #() #{} #Python is cool, no argument here.  @a_decorator_passing_arbitrary_arguments def function_with_arguments(a, b, c):     print(a, b, c)      function_with_arguments(1,2,3) #outputs #Do I have args?: #(1, 2, 3) #{} #1 2 3    @a_decorator_passing_arbitrary_arguments def function_with_named_arguments(a, b, c, platypus="Why not ?"):     print("Do {0}, {1} and {2} like platypus? {3}".format(a, b, c, platypus))  function_with_named_arguments("Bill", "Linus", "Steve", platypus="Indeed!") #outputs #Do I have args ? : #('Bill', 'Linus', 'Steve') #{'platypus': 'Indeed!'} #Do Bill, Linus and Steve like platypus? Indeed!  class Mary(object):          def __init__(self):         self.age = 31          @a_decorator_passing_arbitrary_arguments     def sayYourAge(self, lie=-3): # You can now add a default value         print("I am {0}, what did you think?".format(self.age + lie))  m = Mary() m.sayYourAge() #outputs # Do I have args?: #(<__main__.Mary object at 0xb7d303ac>,) #{} #I am 28, what did you think? 
# Decorators are ORDINARY functions def my_decorator(func):     print("I am an ordinary function")     def wrapper():         print("I am function returned by the decorator")         func()     return wrapper  # Therefore, you can call it without any "@"  def lazy_function():     print("zzzzzzzz")  decorated_function = my_decorator(lazy_function) #outputs: I am an ordinary function              # It outputs "I am an ordinary function", because that’s just what you do: # calling a function. Nothing magic.  @my_decorator def lazy_function():     print("zzzzzzzz")      #outputs: I am an ordinary function 
def decorator_maker():          print("I make decorators! I am executed only once: "           "when you make me create a decorator.")                  def my_decorator(func):                  print("I am a decorator! I am executed only when you decorate a function.")                         def wrapped():             print("I am the wrapper around the decorated function. "                   "I am called when you call the decorated function. "                   "As the wrapper, I return the RESULT of the decorated function.")             return func()                  print("As the decorator, I return the wrapped function.")                  return wrapped          print("As a decorator maker, I return a decorator")     return my_decorator              # Let’s create a decorator. It’s just a new function after all. new_decorator = decorator_maker()        #outputs: #I make decorators! I am executed only once: when you make me create a decorator. #As a decorator maker, I return a decorator  # Then we decorate the function              def decorated_function():     print("I am the decorated function.")     decorated_function = new_decorator(decorated_function) #outputs: #I am a decorator! I am executed only when you decorate a function. #As the decorator, I return the wrapped function       # Let’s call the function: decorated_function() #outputs: #I am the wrapper around the decorated function. I am called when you call the decorated function. #As the wrapper, I return the RESULT of the decorated function. #I am the decorated function. 
def decorated_function():     print("I am the decorated function.") decorated_function = decorator_maker()(decorated_function) #outputs: #I make decorators! I am executed only once: when you make me create a decorator. #As a decorator maker, I return a decorator #I am a decorator! I am executed only when you decorate a function. #As the decorator, I return the wrapped function.  # Finally: decorated_function()     #outputs: #I am the wrapper around the decorated function. I am called when you call the decorated function. #As the wrapper, I return the RESULT of the decorated function. #I am the decorated function. 
@decorator_maker() def decorated_function():     print("I am the decorated function.") #outputs: #I make decorators! I am executed only once: when you make me create a decorator. #As a decorator maker, I return a decorator #I am a decorator! I am executed only when you decorate a function. #As the decorator, I return the wrapped function.  #Eventually:  decorated_function()     #outputs: #I am the wrapper around the decorated function. I am called when you call the decorated function. #As the wrapper, I return the RESULT of the decorated function. #I am the decorated function. 
def decorator_maker_with_arguments(decorator_arg1, decorator_arg2):          print("I make decorators! And I accept arguments: {0}, {1}".format(decorator_arg1, decorator_arg2))                  def my_decorator(func):         # The ability to pass arguments here is a gift from closures.         # If you are not comfortable with closures, you can assume it’s ok,         # or read: https://stackoverflow.com/questions/13857/can-you-explain-closures-as-they-relate-to-python         print("I am the decorator. Somehow you passed me arguments: {0}, {1}".format(decorator_arg1, decorator_arg2))                         # Don't confuse decorator arguments and function arguments!         def wrapped(function_arg1, function_arg2) :             print("I am the wrapper around the decorated function.\n"                   "I can access all the variables\n"                   "\t- from the decorator: {0} {1}\n"                   "\t- from the function call: {2} {3}\n"                   "Then I can pass them to the decorated function"                   .format(decorator_arg1, decorator_arg2,                           function_arg1, function_arg2))             return func(function_arg1, function_arg2)                  return wrapped          return my_decorator  @decorator_maker_with_arguments("Leonard", "Sheldon") def decorated_function_with_arguments(function_arg1, function_arg2):     print("I am the decorated function and only knows about my arguments: {0}"            " {1}".format(function_arg1, function_arg2))            decorated_function_with_arguments("Rajesh", "Howard") #outputs: #I make decorators! And I accept arguments: Leonard Sheldon #I am the decorator. Somehow you passed me arguments: Leonard Sheldon #I am the wrapper around the decorated function.  #I can access all the variables  #   - from the decorator: Leonard Sheldon  #   - from the function call: Rajesh Howard  #Then I can pass them to the decorated function #I am the decorated function and only knows about my arguments: Rajesh Howard 
c1 = "Penny" c2 = "Leslie"  @decorator_maker_with_arguments("Leonard", c1) def decorated_function_with_arguments(function_arg1, function_arg2):     print("I am the decorated function and only knows about my arguments:"            " {0} {1}".format(function_arg1, function_arg2))  decorated_function_with_arguments(c2, "Howard") #outputs: #I make decorators! And I accept arguments: Leonard Penny #I am the decorator. Somehow you passed me arguments: Leonard Penny #I am the wrapper around the decorated function.  #I can access all the variables  #   - from the decorator: Leonard Penny  #   - from the function call: Leslie Howard  #Then I can pass them to the decorated function #I am the decorated function and only know about my arguments: Leslie Howard 
def decorator_with_args(decorator_to_enhance):     """      This function is supposed to be used as a decorator.     It must decorate an other function, that is intended to be used as a decorator.     Take a cup of coffee.     It will allow any decorator to accept an arbitrary number of arguments,     saving you the headache to remember how to do that every time.     """          # We use the same trick we did to pass arguments     def decorator_maker(*args, **kwargs):                 # We create on the fly a decorator that accepts only a function         # but keeps the passed arguments from the maker.         def decorator_wrapper(func):                     # We return the result of the original decorator, which, after all,              # IS JUST AN ORDINARY FUNCTION (which returns a function).             # Only pitfall: the decorator must have this specific signature or it won't work:             return decorator_to_enhance(func, *args, **kwargs)                  return decorator_wrapper          return decorator_maker         
# You create the function you will use as a decorator. And stick a decorator on it :-) # Don't forget, the signature is "decorator(func, *args, **kwargs)" @decorator_with_args  def decorated_decorator(func, *args, **kwargs):      def wrapper(function_arg1, function_arg2):         print("Decorated with {0} {1}".format(args, kwargs))         return func(function_arg1, function_arg2)     return wrapper      # Then you decorate the functions you wish with your brand new decorated decorator.  @decorated_decorator(42, 404, 1024) def decorated_function(function_arg1, function_arg2):     print("Hello {0} {1}".format(function_arg1, function_arg2))  decorated_function("Universe and", "everything") #outputs: #Decorated with (42, 404, 1024) {} #Hello Universe and everything  # Whoooot! 
# For debugging, the stacktrace prints you the function __name__ def foo():     print("foo")      print(foo.__name__) #outputs: foo      # With a decorator, it gets messy     def bar(func):     def wrapper():         print("bar")         return func()     return wrapper  @bar def foo():     print("foo")  print(foo.__name__) #outputs: wrapper  # "functools" can help for that  import functools  def bar(func):     # We say that "wrapper", is wrapping "func"     # and the magic begins     @functools.wraps(func)     def wrapper():         print("bar")         return func()     return wrapper  @bar def foo():     print("foo")  print(foo.__name__) #outputs: foo 
def benchmark(func):     """     A decorator that prints the time a function takes     to execute.     """     import time     def wrapper(*args, **kwargs):         t = time.clock()         res = func(*args, **kwargs)         print("{0} {1}".format(func.__name__, time.clock()-t))         return res     return wrapper   def logging(func):     """     A decorator that logs the activity of the script.     (it actually just prints it, but it could be logging!)     """     def wrapper(*args, **kwargs):         res = func(*args, **kwargs)         print("{0} {1} {2}".format(func.__name__, args, kwargs))         return res     return wrapper   def counter(func):     """     A decorator that counts and prints the number of times a function has been executed     """     def wrapper(*args, **kwargs):         wrapper.count = wrapper.count + 1         res = func(*args, **kwargs)         print("{0} has been used: {1}x".format(func.__name__, wrapper.count))         return res     wrapper.count = 0     return wrapper  @counter @benchmark @logging def reverse_string(string):     return str(reversed(string))  print(reverse_string("Able was I ere I saw Elba")) print(reverse_string("A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal: Panama!"))  #outputs: #reverse_string ('Able was I ere I saw Elba',) {} #wrapper 0.0 #wrapper has been used: 1x  #ablE was I ere I saw elbA #reverse_string ('A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal: Panama!',) {} #wrapper 0.0 #wrapper has been used: 2x #!amanaP :lanac a ,noep a ,stah eros ,raj a ,hsac ,oloR a ,tur a ,mapS ,snip ,eperc a ,)lemac a ro( niaga gab ananab a ,gat a ,nat a ,gab ananab a ,gag a ,inoracam ,elacrep ,epins ,spam ,arutaroloc a ,shajar ,soreh ,atsap ,eonac a ,nalp a ,nam A 
@counter @benchmark @logging def get_random_futurama_quote():     from urllib import urlopen     result = urlopen("http://subfusion.net/cgi-bin/quote.pl?quote=futurama").read()     try:         value = result.split("<br><b><hr><br>")[1].split("<br><br><hr>")[0]         return value.strip()     except:         return "No, I'm ... doesn't!"       print(get_random_futurama_quote()) print(get_random_futurama_quote())  #outputs: #get_random_futurama_quote () {} #wrapper 0.02 #wrapper has been used: 1x #The laws of science be a harsh mistress. #get_random_futurama_quote () {} #wrapper 0.01 #wrapper has been used: 2x #Curse you, merciful Poseidon! 
vote vote

82

from functools import wraps  def makebold(fn):     @wraps(fn)     def wrapper(*args, **kwargs):         return "<b>" + fn(*args, **kwargs) + "</b>"     return wrapper  def makeitalic(fn):     @wraps(fn)     def wrapper(*args, **kwargs):         return "<i>" + fn(*args, **kwargs) + "</i>"     return wrapper  @makebold @makeitalic def hello():     return "hello world"  @makebold @makeitalic def log(s):     return s  print hello()        # returns "<b><i>hello world</i></b>" print hello.__name__ # with functools.wraps() this returns "hello" print log('hello')   # returns "<b><i>hello</i></b>" 
vote vote

80

from functools import wraps  def wrap_in_tag(tag):     def factory(func):         @wraps(func)         def decorator():             return '<%(tag)s>%(rv)s</%(tag)s>' % (                 {'tag': tag, 'rv': func()})         return decorator     return factory 
@wrap_in_tag('b') @wrap_in_tag('i') def say():     return 'hello' 
makebold = wrap_in_tag('b') makeitalic = wrap_in_tag('i')  @makebold @makeitalic def say():     return 'hello' 
from functools import wraps  def wrap_in_tag(tag):     def factory(func):         @wraps(func)         def decorator(val):             return func('<%(tag)s>%(val)s</%(tag)s>' %                         {'tag': tag, 'val': val})         return decorator     return factory 
@wrap_in_tag('b') @wrap_in_tag('i') def say(val):     return val say('hello') 
say = wrap_in_tag('b')(wrap_in_tag('i')(say))) 
vote vote

62

@decorator def func():     ... 
def func():     ... func = decorator(func) 
vote vote

50

def makebold(f):      return lambda: "<b>" + f() + "</b>" def makeitalic(f):      return lambda: "<i>" + f() + "</i>"  @makebold @makeitalic def say():     return "Hello"  print say() 

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