What are some common uses for Python decorators? [closed]

Question

While I like to think of myself as a reasonably competent Python coder, one aspect of the language I've never been able to grok is decorators.

I know what they are (superficially), I've read tutorials, examples, questions on Stack Overflow, and I understand the syntax, can write my own, occasionally use @classmethod and @staticmethod, but it never occurs to me to use a decorator to solve a problem in my own Python code. I never encounter a problem where I think, "Hmm...this looks like a job for a decorator!"

So, I'm wondering if you guys might offer some examples of where you've used decorators in your own programs, and hopefully I'll have an "A-ha!" moment and get them.

Answer 1

I use decorators mainly for timing purposes

def time_dec(func):    def wrapper(*arg):       t = time.clock()       res = func(*arg)       print func.func_name, time.clock()-t       return res    return wrapper   @time_dec def myFunction(n):     ... 

Answer 2

I've used them for synchronization.

import functools  def synchronized(lock):     """ Synchronization decorator """     def wrap(f):         @functools.wraps(f)         def newFunction(*args, **kw):             lock.acquire()             try:                 return f(*args, **kw)             finally:                 lock.release()         return newFunction     return wrap 

As pointed out in the comments, since Python 2.5 you can use a with statement in conjunction with a threading.Lock (or multiprocessing.Lock since version 2.6) object to simplify the decorator's implementation to just:

import functools  def synchronized(lock):     """ Synchronization decorator """     def wrap(f):         @functools.wraps(f)         def newFunction(*args, **kw):             with lock:                 return f(*args, **kw)         return newFunction     return wrap 

Regardless, you then use it like this:

import threading lock = threading.Lock()  @synchronized(lock) def do_something():   # etc  @synchronzied(lock) def do_something_else():   # etc 

Basically it just puts lock.acquire() / lock.release() on either side of the function call.