question about __repr__ in a class

[akbarza]

hi
the below code is in:https://realpython.com/python-mutable-vs...om-classes

class Point:
    def __init__(self, x, y):
        self._x = x
        self._y = y

    @property
    def x(self):
        return self._x

    @property
    def y(self):
        return self._y

    def __repr__(self):
        return f"{type(self).__name__}(x={self.x}, y={self.y})"

what does the last line do also what does the __repe__ method do? how can i use the __repr__ method? if it is omitted, does it cause any problems?
thanks

[deanhystad]

Objects have two string representations: __str__ is the pretty one, and __repr__ is the smart one. __str__ is used when you call str() or print() an object. __repr__ is used when you call repr() or when you print an object as part of a collection (list, dictionary, set, tuple).

Have you tried omitting the method to see what happens? What do you think will happen?

[Gribouillis]

Don't forget to use the search field in the Python documentation

[akbarza]

Objects have two string representations: __str__ is the pretty one, and __repr__ is the smart one. __str__ is used when you call str() or print() an object. __repr__ is used when you call repr() or when you print an object as part of a collection (list, dictionary, set, tuple).

Have you tried omitting the method to see what happens? What do you think will happen?

hi
i omitted it, but i did not see any change. what can i write or add to the above code too see the changes occure with ommitting the __repr__ method?
thanks again for reply

[DeaD_EyE]

If the method __str__ is not available, then __repr__ is called instead.

If you just want a class with some variables and a nice representation, you could use dataclasses instead:

import math
from dataclasses import dataclass


@dataclass
class PointD:
    x: int
    y: int

    @property
    def alpha(self):
        """
        alpha for polar coordinates
        """
        return math.degrees(math.atan2(self.y, self.x))

    @property
    def hypot(self):
        """
        Length of hypot
        """
        return math.hypot(self.x, self.y)

    @property
    def polar(self):
        """
        Poloar coordinates
        """
        return self.alpha, self.hypot

    @classmethod
    def from_ploar(cls, polar):
        """
        Create a point from ploar coordinates

        polar := (alpha, hypot)
        """
        alpha = math.radians(polar[0])
        return cls(math.cos(alpha) * polar[1], math.sin(alpha) * polar[1])


p2 = PointD(7, 9)
print(p2)
print(f"{p2!s}")
print(f"{p2!r}")
print(f"{p2.alpha}")
print(f"{p2.hypot}")
print(f"{p2.polar}")
print(PointD.from_ploar(p2.polar))

Output:
PointD(x=7, y=9)
PointD(x=7, y=9)
PointD(x=7, y=9)
52.1250163489018
11.40175425099138
(52.1250163489018, 11.40175425099138)
PointD(x=6.999999999999998, y=9.0)