Python - Name format_string is not defined error

Question

I'm trying to create a class tree from which I can create various files and insert a list of values.I have only included code for the Delimited file. Whilst running the below code,I get the message that appears in the title, please assist.Thanks

from datetime import datetime as Dt
from abc import abstractmethod,ABCMeta

class FileWriter(metaclass=ABCMeta):     

    def __init__(self,FileName):
        self.FileName = FileName

    @staticmethod
    def return_time():
        return Dt.now().strftime('%Y-%m-%d %H:%M')

    @abstractmethod
    def write(self):
        return


    def format_string(self,Values,Seperator,CSV = False):
        self.Values = Seperator.join((Values))
        if CSV == True:self.Values = Seperator.join((Values))
        return self.Values

    def write_lines(self,Values,Seperator = ","):

        print(self.Values)
        File = open(self.FileName,'w')
        File.write(self.Values + '\n')
        File.close()

class DelimitedFile(FileWriter):

    def __init__(self, FileName):
        return super().__init__(FileName)

    def format_string(self, Values, Seperator):
        self.Values = Values
        self.Seperator = Seperator
        for i in range(len(self.Values)):
            if "," in self.Values[i]:self.Values[i] = ('"' + self.Values[i] + '"')
        self.Seperator = Seperator
        return super().format_string(Values, Seperator) + ','

    def write(self,Values,Seperator=',',CSV = False):
        self.Values = str(Values)
        self.Seperator = Seperator
        self.Values = format_string(self.Values,self.Seperator)
        super().write_lines(self.Values,Seperator=',')

NewInst = DelimitedFile('Test.txt')
print(NewInst.return_time())
Values = ['s','str','trtyh','yutyuty','u7u7u7u7','e5ryru,tut','u7u7tussth','y5syyjuyju']
NewInst.write(Values)
Value = (NewInst.format_string(Values,','))