Constructing a class in python without directly calling the constructor

Question

In python if we define a class called Start and initialize it with an argument as seen below...

class Start:
   def __init__(self, a):
      self.a = a

Once defined, and after importing Start into another python file is there any way to make a function or attribute inside the class so I can construct the class directly like this?

# Start.make or Start.make()
# Sample usage below
s = Start.make #initializes Start with the argument of 1

What I'm trying to do is to have Start.make accomplish the same objective as Start(1) so I can potentially create other method of constructing commonly used values without having to manually place the arguments inside the Start() constructor. Is this in anyway possible in Python? If not, are there any alternatives solutions I can follow to achieve a similar result?

lmiguelvargasf · Accepted Answer · 2020-07-11 18:32:59Z

1

You can use a static method, or you can also use a class method:

class Start:
    def __init__(self, a):
        self.a = a

    @classmethod
    def make(cls):
        return cls(1)

To create an instance use the following:

>>> s = Start.make()
>>> s.a
1

answered Jul 11, 2020 at 18:32

lmiguelvargasf

71.2k55 gold badges231 silver badges239 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

chepner Over a year ago

This is exactly what class methods are intended for: defining alternate constructors for a class.

Michael Butscher · Accepted Answer · 2020-07-11 18:25:10Z

1

With a static method:

class Start:
    def __init__(self, a):
        self.a = a

    @staticmethod
    def make():
        return Start(1)

s = Start.make()

answered Jul 11, 2020 at 18:25

Michael Butscher

11k4 gold badges28 silver badges28 bronze badges

2 Comments

PensivePastuer Over a year ago

Are there any caveats to using a static method in python?

chepner Over a year ago

@PensivePastuer make will always return an instance of Start, even if you subclass Start. A class method is more flexible; static methods aren't commonly used in Python, as they essentially just wrap a regular function in the namespace of a class.

Collectives™ on Stack Overflow

Constructing a class in python without directly calling the constructor

2 Answers 2

1 Comment

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related