color version - PET: Python Entre Todos - Python Argentina

def sum(a, b):
return a + b
def my_function(some, arguments):
# function's body
sum = d(sum)
Is equivalent to:
@d
def sum(a, b):
return a + b
In the above code snippet you can see two examples where we compare the different
ways of applying a decorator.
Next there are some examples of real decorators.
Warning
Counter-example: the evil decorator.
def evil(f):
return False
>>> @evil
... def something():
... return 42
...
>>> something
False
>>> something()
Traceback (most recent call last):
File "", line 1, in
TypeError: 'bool' object is not callable
This is a cheater decorator, because instead of returning a new function, it returns a
boolean object. Obviously when we try to run it, we get an error.
Chained decorators
Their application is similar to the mathematical concept of function composition.
@register_use
@measure_execution_time
def my_function(some, arguments):
# function's body
my_function = register_use(measure_execution_time(my_function))
Decorators with parameters
• They allow more flexible decorators.
• Example: a decorator that forces a return type of a function.
Suppose we want a decorator that converts to string all a function’s returns. You could
use this way:
@to_string
def count():
return 42
>>> count()
'42'
How would you implement that See a first approach:
def to_string(f):
def inner(*args, **kwargs):
return str(f(*args, **kwargs))
return inner
This way works, but think if we can do this in a more generic way. Below you’ll find the
use form of a decorator named typer:
@typer(str)
def c():
return 42