CODEWITHSUNDEEP
pythonclassoopinitializationfactory
Peter Pik
Peter Pik

Reputation: 11193

Create an instance in a class method in Python

I am trying to create DataType class to reflect data types in a SQL database. Since data types require different information like size, precision etc. different parameters need to be specified when creating an instance.

I want to be able to call it with something like DataType.createVarChar(size, charSet). So far I have written the code below but I am not sure whether it is the correct way to do it since I am originally creating an object at the start without providing any information in it.

What would be the correct design in this case?

class SQLDatatype(Enum):
    UNSUPPORTED,
    VARCHAR


class DataType(object):

    def __init__(self, dataType=None, precision=None, scale=None, size=None, charSet=None):
        self.dataType = dataType
        self.precision = precision
        self.scale = scale
        self.size = size
        self.withLocalTimezone = withLocalTimezone
        self.charSet = charSet

    def createVarChar(self, size, charSet):
        return Datatype(dataType=SQLDataType.VARCHAR, size=size, charSet=charSet)

Upvotes: 2

Views: 3520

Answers (2)

Jonas Adler
Jonas Adler

Reputation: 10809

The standard way would be to create a function:

def createVarChar(size, charSet):
    return Datatype(dataType=SQLDataType.VARCHAR, size=size, charSet=charSet)

The other option is to create a class method:

class DataType(object):
    ...
    @classmethod
    def createVarChar(cls, size, charSet):
        return cls(dataType=SQLDataType.VARCHAR, size=size, charSet=charSet)

This allows this method to work correctly with inheritance, which a free function would not.

Upvotes: 5

Danil Speransky
Danil Speransky

Reputation: 30473

You may use @classmethod:

@classmethod
def createVarChar(cls, size, charSet):
    return cls(dataType=SQLDataType.VARCHAR, size=size, charSet=charSet)

Upvotes: 2

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