Write class such that calling instance returns all instance variables

问题

I have answered my own question - see answer below
I'm writing a class, and I want this behavior:

a = f(10,20)
some_funct(a.row) # some_function is given 10
some_funct(a.col) # some_function is given 20
some_funct(a)     # some_function is given a tuple of 10, 20  <-- THIS ONE :)

The last behavior is stumping me. I have not seen any examples that cover this.

Thus far:

class f(object):
    """Simple 2d object"""
    row: int
    col: int

    def __init__(self, row, col):
        self.row = row
        self.col = col

Explictly I do not want another method, say, self.both = row, col. I just want to 'call' the instance

I'm new to classes, so any improvements are welcome. Properties, setters, getters etc.

EDIT 1: Replaced "print" with "some_function" in the question, and modified title

回答1:

You can do like this

class f(object):
    """Simple 2d object"""
    row: int
    col: int

    def __init__(self, row, col):
        self.row = row
        self.col = col

    def __str__(self):
        return f"row = {row}, col = {col}"

and print like this

a = f(10,20)

print(a)     # row = 10, col = 20

回答2:

This might help


class f(object):
    """Simple 2d object"""
    row: int
    col: int

    def __init__(self, row, col):
        self.row = row
        self.col = col

    def some_funct(self):
        return (self.row, self.col)

You can access like

a = f(10,20)
a.some_funct() # (10, 20)
# or
row, col = a.some_funct()

回答3:

From python 3.7 dataclasses have been introduced and their goal is to create classes that mainly contains data. Dataclasses comes with some helper function that extract the class attributes dict/tuples. e.g.

from dataclasses import dataclass,asdict,astuple
@dataclass
class f:
 x: int
 y: int

f_instance = f(10,20)
asdict(f_instance) # --> {'x': 10, 'y': 20}
astuple(f_instance) # -> (10,20)

EDIT I : Another technique would be to use namedtuple e.g.:

from collections import namedtuple
f = namedtuple('p',['row','col'])
a =f(10,20)
a.row #-> 10
a.col #-> 20

回答4:

class f(tuple):
    """Simple 2d object"""
    def __new__(cls, x, y):
        return tuple.__new__(f, (x, y))

    def __init__(self, x, y):
        self.col = x
        self.row = y

foo = f(1,2)
print(foo.col)
>>>1
print(foo.row)
>>>2
print(foo)
>>>(1, 2)

Importantly:
If you want it to behave like a tuple then make it a subclass of tuple.

Much stuffing around but stumbled upon an external site which gave me clues about the keywords to search on here. The SO question is here but I have modified that answer slightly.
I'm still a little confused because the other site says to use new in the init as well but does not give a clear example.

来源：https://stackoverflow.com/questions/66040586/write-class-such-that-calling-instance-returns-all-instance-variables

标签

python-3.x

class

return

subclass

subclassing