Python syntax and semantics
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Decorators can be chained by placing several on adjacent lines:
@invincible
@favourite_colour("Blue")
def black_knight():
pass
is equivalent to
def black_knight():
pass
black_knight = invincible(favourite_colour("Blue")(black_knight))
or, using intermediate variables
def black_knight():
pass
blue_decorator = favourite_colour("Blue")
decorated_by_blue = blue_decorator(black_knight)
black_knight = invincible(decorated_by_blue)
In the example above, the favourite_colour decorator factory takes an argument. Decorator factories must return a decorator, which is then called with the object to be decorated as its argument:
def favourite_colour(colour):
def decorator(func):
def wrapper():
print(colour)
func()
return wrapper
return decorator
This would then decorate the black_knight function such that the colour, "Blue", would be printed prior to the black_knight function running. Closure ensures that the colour argument is accessible to the innermost wrapper function even when it is returned and goes out of scope, which is what allows decorators to work.
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