CODEWITHSUNDEEP
pythonpython-3.xoop
Greg
Greg

Reputation: 8945

How to make a Class return an object when the class is referenced after it has been initialized?

How to make a class return an object in the following way:

import numpy as np

a = np.array([(1,2),(3,4)])

Whenever a is referenced, it returns 

array([[1, 2],
       [3, 4]])

However when I create a simple class:

class Example:
    def __init__(self, data):
        self.nparray = np.array(data)

And run b = Example([(1,2),(3,4)]) then reference b I get: <__main__.Example at 0x7f17381099e8>. To return the value I need to run b.nparray.

How to make the class Example return 

array([[1, 2],
       [3, 4]])

when b is referenced?

I tried using methods such as __new__, __repr__ and __getitem__ however none produced the desired behavior.

Upvotes: 0

Views: 66

Answers (3)

Dimitris Fasarakis Hilliard
Dimitris Fasarakis Hilliard

Reputation: 160647

You should use __repr__ in the following way:

class Example:
    def __init__(self, data):
            self.nparray = np.array(data)
    def __repr__(self):
            return repr(self.nparray)

This returns the representation the self.nparray object within:

>>> c = Example([(1, 2), (3, 4)])
>>> c
array([[1, 2],
       [3, 4]])

Of course this is used and during interactive sessions where you simply enter the name and press enter and if you print it with print(c). If you need to limit to only for print calls you define __str__ for the object in question.

Upvotes: 2

Thomas Knox
Thomas Knox

Reputation: 1

You can't return any data from a class init function. Have you tried something like:

class Example(object):
    nparray = None
    def __init__(self, data):
        self.nparray = np.array(data)
        return

    def getArray(self):
        return(self.nparray)

Upvotes: 0

Aaron Christiansen
Aaron Christiansen

Reputation: 11837

Using Python's "magic methods", like the __init__ you've already seen, we can make the class execute code when certain things happen. One of these is __call__, which executes when the class is called like a function.

Knowing this, you could use this code:

import numpy as np

class Example:
    def __init__(self, data):
        self.nparray = np.array(data)

    def __call__(self):
        # This function is called when an instance of Example is called
        return self.nparray

The result of this:

>>> b = Example([[1, 2], [3, 4]])
>>> b()
array([[1, 2],
       [3, 4]])

For more on magic methods, see this useful article.

Upvotes: 2

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