🔒 decorator behind the scenes | Python | Page 1

robust remnantBOT Sep 17, 2025, 7:06 PM

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@abstract frigate

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ivory rock Sep 17, 2025, 7:07 PM

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would you be able to tell me what happens when running this?

def foo(f):
    f()

def bar():
    print("Yay!")


foo(bar)

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Yes, do you understand why? Do you see how we can pass bar as an argument to the function call?

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Ok good, this is important to understand for how decorators work

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a decorator is a function that returns a function

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def call_twice(f):
    def wrapper():
        f()
        f()
    return wrapper

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here's a simple example

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!e

def call_twice(f):
    def wrapper():
        f()
        f()
    return wrapper


@call_twice
def foo():
    print("Yay!")


foo()

robust remnantBOT Sep 17, 2025, 7:12 PM

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ivory rock !e ```py def call_twice(f): def wrapper(): f() f() retur...

:white_check_mark: Your 3.13 eval job has completed with return code 0.

001 | Yay!
002 | Yay!

ivory rock Sep 17, 2025, 7:12 PM

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if I decorate any function with @call_twice, it will call it twice instead of once

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this decoration is the equivalent of this

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foo = call_twice(foo)

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@abstract frigate Are you with me still?

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Ok, I just need to see what your understanding of basic decorators is first

tulip wraith Sep 17, 2025, 7:16 PM

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ivory rock a decorator is a function that returns a function

just a side note here but, u can do a LOT more with decorators than just decorate using functions that returns functions, thats just one of the main uses pithink

ivory rock Sep 17, 2025, 7:17 PM

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ignoring the setter for a moment, a property decorator is basically the same as my example above

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class Human:
    def __init__(self, firstName, lastName):
        self.firstName = firstName
        self.lastName = lastName
        
    def full_name(self):
        return self.firstName + ' ' + self.lastName
        
    
    full_name = property(full_name)

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we're just wrapping property() around our method name

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!e

class Human:
    def __init__(self, firstName, lastName):
        self.firstName = firstName
        self.lastName = lastName
        
    def full_name(self):
        return self.firstName + ' ' + self.lastName
        
    
    full_name = property(full_name)


my_human = Human('John', 'Smith')
print(my_human.full_name)

robust remnantBOT Sep 17, 2025, 7:17 PM

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ivory rock !e ```py class Human: def __init__(self, firstName, lastName): self....

:white_check_mark: Your 3.13 eval job has completed with return code 0.

John Smith

ivory rock Sep 17, 2025, 7:19 PM

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@property does, yes

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when we create a property, we can give it a getter, a setter, and a deleter

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the decorator syntax is smart and handles methods with duplicate names

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but if we didn't want to use decorators, we'd need unique names

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yes, it has a setter method

tulip wraith Sep 17, 2025, 7:21 PM

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indeed

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>>> type(property())
<class 'property'>
>>>

ivory rock Sep 17, 2025, 7:22 PM

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!e

from re import fullmatch


class Human:
    def __init__(self, firstName, lastName):
        self.firstName = firstName
        self.lastName = lastName
        
    def full_name(self):
        return self.firstName + ' ' + self.lastName


    def set_full_name(self, value):
        self.firstName, self.lastName = value.split()
        
    
    full_name = property(full_name, set_full_name)


my_human = Human('John', 'Smith')
print(my_human.full_name)
my_human.full_name = 'Jane Doe'
print(my_human.full_name)

robust remnantBOT Sep 17, 2025, 7:22 PM

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ivory rock !e ```py from re import fullmatch class Human: def __init__(self, firstNam...

:white_check_mark: Your 3.13 eval job has completed with return code 0.

001 | John Smith
002 | Jane Doe

ivory rock Sep 17, 2025, 7:22 PM

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not a decorator in sight

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idk how that re import got in there, haha

tulip wraith Sep 17, 2025, 7:23 PM

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just one more thing about decorators, u can stack them pithink

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!e

@print
@lambda func: func()
def watever():
    return 4

robust remnantBOT Sep 17, 2025, 7:26 PM

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tulip wraith !e ```py @print @lambda func: func() def watever(): return 4 ```

:white_check_mark: Your 3.13 eval job has completed with return code 0.

tulip wraith Sep 17, 2025, 7:27 PM

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the first decorator calls the function then the 2nd decorator gets result from that and uses it

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thats why u end up with printing 4

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that code is essentially the same as print(watever())

robust remnantBOT Sep 17, 2025, 8:08 PM

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:warning: The owner of this post is no longer in the server.

tulip wraith Sep 17, 2025, 8:08 PM

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huh

robust remnantBOT Sep 17, 2025, 8:11 PM

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#🔒 decorator behind the scenes