An example and explaination of a Python decorator that takes a non-optional parameter.

decorator_with_param.py

""" An example of writing a decorator that takes an argument.

Based on e-satis's answer at http://stackoverflow.com/questions/739654/understanding-python-decorators#1594484.
"""

from functools import wraps

# The outer-most level is the decorator factory.  The middle level is the 
# decorator and the inner most level is where we call the decorated function.
def decorator_maker(buzz):
    """ Returns a decorator. 
    
    If buzz is True, then will make decorated functions say 'BUZZ!'.
    """
    def dec(func):
        """ Decorates a function. """
        # Use wraps() to preserve information about the wrapped function.
        @wraps(func)
        def wrapper(*args, **kwargs):
            """ Calls the decorated (wrapped) function. """
            if buzz:
                print "BUZZ!"
            return func(*args, **kwargs)
        return wrapper
    return dec
            
if __name__ == '__main__':     
    # These below are progressivly more compact ways to achieve the decoration 
    # effect w/o using @decorator syntax.  For illustration only.
    def func(x, y=None):
        print x, y
    
    decorator = decorator_maker(True)
    decorated_func = decorator(func)
    decorated_func(1, y=2)
    
    decorated_func = decorator_maker(True)(func)
    decorated_func(1, y=2)
    
    decorator_maker(True)(func)(1, y=2)
    
    # This below is how to call the decorator w/ optional args.
    @decorator_maker(True)
    def func2(x, y=None):
        print x, y
        
    func2(1, y=2)