🔒 after learning decorators i reached there | Python | Page 1

tall ether Apr 20, 2026, 6:29 AM

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I don't why the tutor wrote like this...please help me understand this

little mangoBOT Apr 20, 2026, 6:29 AM

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tall ether I don't why the tutor wrote like this...please help me understand this

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@tall ether

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heavy silo Apr 20, 2026, 6:32 AM

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tall ether I don't why the tutor wrote like this...please help me understand this

what specific thing are you asking about?

tall ether Apr 20, 2026, 6:33 AM

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what is cache and why he wrote self._area = None in the first part

heavy silo Apr 20, 2026, 6:33 AM

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Do you understand what this class is being used for?

tall ether Apr 20, 2026, 6:34 AM

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to find area of the circle?

heavy silo Apr 20, 2026, 6:34 AM

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Well yes

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but when it is constructed, it is only given a radius

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so I can make Circle(5)

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the area is not calculated until it is asked for though

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the instance also has a property setter to change the radius

tall ether Apr 20, 2026, 6:35 AM

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but it is in the init

heavy silo Apr 20, 2026, 6:35 AM

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Yes, but it is not a parameter

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you can have attributes that are not parameters

tall ether Apr 20, 2026, 6:35 AM

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heavy silo you can have attributes that are not parameters

and how to call it

heavy silo Apr 20, 2026, 6:35 AM

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I'm not sure what you're asking

tall ether Apr 20, 2026, 6:36 AM

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how to call init attribute who has no parameter

heavy silo Apr 20, 2026, 6:36 AM

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it's still just an attribute

tall ether Apr 20, 2026, 6:36 AM

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what is the use of it

heavy silo Apr 20, 2026, 6:36 AM

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class Car:

    def __init__(self, color):
        self.color = color
        self.fuel = 0

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in this example, all my car instances start with 0 fuel

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I don't need a parameter to tell me that

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and it's not something I want to be controlled when the instance is created (for this example)

heavy silo Apr 20, 2026, 6:37 AM

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tall ether what is the use of it

parameters are just the attributes that we want to be determined by the constructor

tall ether Apr 20, 2026, 6:37 AM

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ok but it can be modified in runtime?

heavy silo Apr 20, 2026, 6:37 AM

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yes

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it's just not decided during instantiation

tall ether Apr 20, 2026, 6:37 AM

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okay

heavy silo Apr 20, 2026, 6:38 AM

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so in your circle example, the area is only first calculated when asked for

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if it's the first time we ask for area, it has to be calculated

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if we ask for area more than once, then we just use the previously calculated value (no point in calculating it more than once since it will be the same result)

tall ether Apr 20, 2026, 6:40 AM

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didn't get it

heavy silo Apr 20, 2026, 6:40 AM

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if I ask you "what is the area of a circle with radius 5", what would you say to me?

tall ether Apr 20, 2026, 6:41 AM

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i have radius of 5

heavy silo Apr 20, 2026, 6:41 AM

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no, I'm asking you for the area

tall ether Apr 20, 2026, 6:41 AM

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none

heavy silo Apr 20, 2026, 6:41 AM

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I'm asking you, wizard

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I'm giving you an example

tall ether Apr 20, 2026, 6:42 AM

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oh mb

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pi r square

heavy silo Apr 20, 2026, 6:42 AM

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hey wizard, what is the area of a circle with the radius 5?

tall ether Apr 20, 2026, 6:42 AM

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do i calculate?

heavy silo Apr 20, 2026, 6:42 AM

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yes

tall ether Apr 20, 2026, 6:43 AM

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78.57

heavy silo Apr 20, 2026, 6:43 AM

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great

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hey wizard, what is the area of a circle with radius 5?

tall ether Apr 20, 2026, 6:43 AM

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man!!..is it still wrong

heavy silo Apr 20, 2026, 6:43 AM

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no, it is correct

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but, I'm asking you the same question two times in a row

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which means you shouldn't need to calculate it again

tall ether Apr 20, 2026, 6:44 AM

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78.57

heavy silo Apr 20, 2026, 6:44 AM

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yes exactly 🙂

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instead of doing the calculation again, you can just say "oh, this is the same question as last time, I already have the answer"

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that's what is happening here

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"if we haven't calculated the area yet, then we should calculate it now"

tall ether Apr 20, 2026, 6:46 AM

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ohkk

heavy silo Apr 20, 2026, 6:47 AM

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and that's why we need this. If we change the radius of the circle, we have to say "our previous area calculation is no longer correct"

tall ether Apr 20, 2026, 6:49 AM

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it has to click but it didnt

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second last part is clear to me btw

heavy silo Apr 20, 2026, 6:50 AM

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hey wizard, what is the area of a circle with the radius 5?

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@tall ether still there?

tall ether Apr 20, 2026, 6:55 AM

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yes i am

heavy silo Apr 20, 2026, 6:56 AM

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what is the area of a circle with the radius 5?

tall ether Apr 20, 2026, 6:56 AM

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78.57

heavy silo Apr 20, 2026, 6:56 AM

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hey wizard, what is the area of a circle with radius 8?

tall ether Apr 20, 2026, 6:57 AM

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wait...is the last method called after init?

heavy silo Apr 20, 2026, 6:57 AM

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no, only init is called when the instance is created

tall ether Apr 20, 2026, 6:58 AM

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and property returns getter only?

heavy silo Apr 20, 2026, 6:58 AM

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yes, but your radius also has a setter

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can you paste the code of this class?

tall ether Apr 20, 2026, 6:59 AM

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its in my phone

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its a video ss

heavy silo Apr 20, 2026, 7:00 AM

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you should really try writing out the code and running it

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you should pretty much never learn new code without also writing it and running it

tall ether Apr 20, 2026, 7:00 AM

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okay..give me time..i am going to..

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ok, so it will always return the area none when we initialise or put a new radius..right? @heavy silo

heavy silo Apr 20, 2026, 7:14 AM

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it's not returning anything yet, it's just storing a placeholder value until the first area is actually calculated

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c = Circle(5)
print(c.area)

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you would use it like this

tall ether Apr 20, 2026, 7:16 AM

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yes ok

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import math
class Circle:
    def __init__(self, r):
        self._r = r
        self._area = None

    @property
    def radius(self):
        return self._r

    @radius.setter
    def radius(self, r):
        if r < 0:
            raise ValurError('Radius must be a non negative')
        self._r = r
        self._area = None

    @property
    def area(self):
        if self._area is None:
            self._area = math.pi * (self.radius ** 2)
        return self._area```

heavy silo Apr 20, 2026, 7:18 AM

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ok, I've added a print to the area property so it will display when it has to recalculate the area

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!e

import math
class Circle:
    def __init__(self, r):
        self._r = r
        self._area = None

    @property
    def radius(self):
        return self._r

    @radius.setter
    def radius(self, r):
        if r < 0:
            raise ValurError('Radius must be a non negative')
        self._r = r
        self._area = None

    @property
    def area(self):
        if self._area is None:
            print("CALCULATING...")
            self._area = math.pi * (self.radius ** 2)
        return self._area


c = Circle(5)
print(c.area)
print(c.area)
print(c.area)

little mangoBOT Apr 20, 2026, 7:18 AM

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heavy silo !e ```py import math class Circle: def __init__(self, r): self._r = ...

:white_check_mark: Your 3.14 eval job has completed with return code 0.

001 | CALCULATING...
002 | 78.53981633974483
003 | 78.53981633974483
004 | 78.53981633974483

heavy silo Apr 20, 2026, 7:18 AM

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See how it only says CALCULATING once, even though I've asked for the area 3 times?

tall ether Apr 20, 2026, 7:19 AM

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why

heavy silo Apr 20, 2026, 7:19 AM

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heavy silo instead of doing the calculation again, you can just say "oh, this is the same q...

.

heavy silo Apr 20, 2026, 7:20 AM

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heavy silo if it's the *first* time we ask for area, it has to be calculated

.

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make sure you read everything I say carefully

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this is exactly what your class is doing by the way. The answer has previously been answered, so it's pointing at the same answer instead of calculating it again

tall ether Apr 20, 2026, 7:24 AM

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ah..so it is saving in the self._area attribute instead of none

heavy silo Apr 20, 2026, 7:24 AM

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yes, so it can look it up again

tall ether Apr 20, 2026, 7:24 AM

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oh ok

heavy silo Apr 20, 2026, 7:24 AM

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if the radius changes, we're discarding the old area value since it is no longer correct

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!e

import math
class Circle:
    def __init__(self, r):
        self._r = r
        self._area = None

    @property
    def radius(self):
        return self._r

    @radius.setter
    def radius(self, r):
        if r < 0:
            raise ValurError('Radius must be a non negative')
        self._r = r
        self._area = None

    @property
    def area(self):
        if self._area is None:
            print("CALCULATING...")
            self._area = math.pi * (self.radius ** 2)
        return self._area


c = Circle(5)
print(c.area)
print(c.area)
print(c.area)
c.radius = 10
print(c.area)
print(c.area)

little mangoBOT Apr 20, 2026, 7:25 AM

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heavy silo !e ```py import math class Circle: def __init__(self, r): self._r = ...

:white_check_mark: Your 3.14 eval job has completed with return code 0.

001 | CALCULATING...
002 | 78.53981633974483
003 | 78.53981633974483
004 | 78.53981633974483
005 | CALCULATING...
006 | 314.1592653589793
007 | 314.1592653589793

heavy silo Apr 20, 2026, 7:25 AM

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here I've changed the radius to 10 so it has to recalculate

tall ether Apr 20, 2026, 7:25 AM

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heavy silo if the radius changes, we're discarding the old area value since it is no longer...

aif radius changes, the area comes back to none ,, right

heavy silo Apr 20, 2026, 7:25 AM

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yes

tall ether Apr 20, 2026, 7:25 AM

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ohkk

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got it

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nice..i can move forward now

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thank you fashoomp

heavy silo Apr 20, 2026, 7:26 AM

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np 🙂

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you should try and write this class again by yourself

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open a new file and try

tall ether Apr 20, 2026, 7:26 AM

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okay

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bye

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i am closing this

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!close

little mangoBOT Apr 20, 2026, 7:27 AM

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Python help channel closed with !close

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#🔒 after learning decorators i reached there