Python empty constructor

Question

Is there any way to create an empty constructor in python. I have a class:

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

now I initialize it like this:

p = Point(0, 5, 10)

How can I create an empty constructor and initialize it like this:

p = Point()

And what should the x, y and z of the second version be? Don't you just want default arguments? Have you tried reading a tutorial or doing some research? — jonrsharpe
– jonrsharpe, Commented Mar 19, 2017 at 9:10

Waxrat · Accepted Answer · 2017-03-19 09:11:35Z

56

class Point:
    def __init__(self):
        pass

answered Mar 19, 2017 at 9:11

Waxrat

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3 Comments

jonrsharpe Over a year ago

But this cannot coexist with the current implementation. Only one method with that name will be retained.

Donald Duck is with Ukraine Over a year ago

While this code may answer the question, providing additional context regarding how and/or why it solves the problem would improve the answer's long-term value.

HoldOffHunger Over a year ago

In place of "pass", "1" also would have worked, or any null operation. See more: docs.python.org/2.0/ref/pass.html

Shreyash S Sarnayak · Accepted Answer · 2017-03-19 09:29:44Z

26

As @jonrsharpe said in comments, you can use the default arguments.

class Point:
    def __init__(self, x=0, y=0, z=0):
        self.x = x
        self.y = y
        self.z = z

Now you can call Point()

answered Mar 19, 2017 at 9:29

Shreyash S Sarnayak

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1 Comment

Kai Zheng Over a year ago

This works, but be careful. Passing over any mutable types (objects, arrays...) will make it shared between all instances.

William Pearsall · Accepted Answer · 2020-09-10 12:21:19Z

15

You can achieve your desired results by constructing the class in a slightly different manner.

class Point:
    def __init__(self):
        pass

    def setvalues(self, x, y, z):
        self.x = x
        self.y = y
        self.z = z

edited Sep 10, 2020 at 12:21

answered Jul 11, 2019 at 16:20

William Pearsall

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2 Comments

RCross Over a year ago

Shouldn't setvalues take 'self' as the first argument? Also, shouldn't all those instance variables be defined in __init__?

William Pearsall Over a year ago

@RCross yeah it should have self as the first arg, edited to reflect. The constructor wouldn't be empty if we had instance variable declarations in it however. I agree that it isn't pythonic however.

Graham · Accepted Answer · 2017-09-26 21:58:02Z

13

You should define the __init__() method of your Point class with optional parameters.

In your case, this should work:

class Point:
    def __init__(self, x=0, y=0, z=0):
        self.x = x
        self.y = y
        self.z = z

pointA = Point(0, 5, 10)
print("pointA: x={}, y={}, z={}".format(pointA.x, pointA.y, pointA.z))
# print "pointA: x=0, y=5, z=10"

pointB = Point()
print("pointB: x={}, y={}, z={}".format(pointB.x, pointB.y, pointB.z))
# print "pointB: x=0, y=0, z=0"

edited Sep 26, 2017 at 21:58

Graham

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answered Mar 19, 2017 at 9:31

PurpleJo

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1 Comment

seanahern Over a year ago

This is the best answer. It covers all of the ground that the original question asks about.

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