How to make a python object return attribute data when called directly

Question

So i want to something like this in Python:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __repr__(self):
        return self.name, self.age

p = Person('A', 20)

Then hope to call object p directly to get the tuple (self.name, self.age)

But as you can see when you run this program, you get the problem:

TypeError: __repr__ returned non-string (type tuple)

How can have this behavior?

Thanks!

Note: The problem is not specific to the tuple data type; it can be anything, like a pandas dataframe for example. I just want to return some attribute data, whatever type it is.

Do you want (self.name, self.age) as a string, or as an actual tuple? — PM 2Ring
– PM 2Ring, Commented Aug 3, 2018 at 12:18
Is that the full definition of your actual Person class, or does it also have other methods? If you don't need methods, you could use a namedtuple, or the new dataclass. — PM 2Ring
– PM 2Ring, Commented Aug 3, 2018 at 12:21
Well this is a simplified model of my problem. It is not specific to the tuple datatype but can be anything like a dataframe for example. The importance is the concept i want to discover: How to actually return attribute data when the object is called directly (rather than returning its memory address) — moctarjallo
– moctarjallo, Commented Aug 3, 2018 at 12:29
@mctrjalloh Ok but what do you mean by called directly, what is that ? — scharette
– scharette, Commented Aug 3, 2018 at 12:30

scharette · Accepted Answer · 2018-08-03 12:22:54Z

5

As the error suggest, your __repr__ must return a string

def __repr__(self):
    return self.name + str(self.age)

Now, if your goal is to write a custom way of representing your object as a tuple, what you are looking for is _iter__ instead,

def __iter__(self):
    yield self.name
    yield self.age

p = Person('A', 20)
print(tuple(p))
>>>>('A', 20)

edited Aug 3, 2018 at 12:22

answered Aug 3, 2018 at 12:09

scharette

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5 Comments

moctarjallo Over a year ago

I want to return the tuple itself, or any data that is available in the object attributes. But not the string representation. That was just an attempt.

scharette Over a year ago

@mctrjalloh Just want to make sure I correctly understood your problem, could you please give more detail on what you mean by called directly. Do you want to return a tuple when you use p() ?

moctarjallo Over a year ago

Now let's say rather than being a tuple it was a pandas dataframe i wanted to return...

scharette Over a year ago

@mctrjalloh You're still not answering what you mean by called directly.

moctarjallo Over a year ago

NO. just by typing p without the parentheses

chepner · Accepted Answer · 2018-08-03 12:21:40Z

1

You can make Person iterable:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __iter__(self):
        yield self.name
        yield self.age

name, age = p

answered Aug 3, 2018 at 12:21

chepner

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3 Comments

PM 2Ring Over a year ago

Alternatively, def __iter__(self): yield from (self.name, self.age)

chepner Over a year ago

Depends on what you mean. A Person iterator yields its name and age in succession; what you do with that is a separate issue.

PM 2Ring Over a year ago

@mctrjalloh If you want a dataframe, why use a class at all? Just make a function that takes the args you want and returns the desired dataframe.

PM 2Ring · Accepted Answer · 2018-08-03 12:28:04Z

1

Another option is to make the class instance callable, and return the desired tuple when called. Eg,

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __repr__(self):
        return f'Person({self.name}, {self.age})'

    def __call__(self):
        return self.name, self.age

p = Person('A', 20)
print(p)
t = p()
print(t, type(t))

output

Person(A, 20)
('A', 20) <class 'tuple'>

answered Aug 3, 2018 at 12:28

PM 2Ring

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Comments

maor10 · Accepted Answer · 2018-08-03 12:18:02Z

0

Adding on, maybe you're looking for a namedtuple- it would give you exactly what you're looking for:

from collections import namedtuple
Person = namedtuple('Person', 'name, age')

So you'd basically get a tuple every time you created a person (you'd get unpacking and such)- however, the object person will be immutable, not sure if that's what you're shooting for here.

answered Aug 3, 2018 at 12:18

maor10

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2 Comments

guidot Over a year ago

This proposal no longer holds as soon as a real method is required, like is_of_age().

maor10 Over a year ago

Again, it depends what he's looking for. "Then hope to call object p directly to get the tuple (self.name, self.age)"

guidot · Accepted Answer · 2018-08-03 12:28:00Z

0

Since __repr__is supposed to return something, which looks like a valid Python expression, you may choose to implement __str__ instead (even if this implementation would fit both purposes):

def __str__(self):
    return "Person({}, {})".format(self.name, self.age)

Update: If a tuple is actually desired, you simply have to use an non-predefined routine:

def get_attributes(self):
    return self.name, self.age

edited Aug 3, 2018 at 12:28

answered Aug 3, 2018 at 12:17

guidot

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