validate_required_params.py

@staticmethod
    def validate_required_input(param, value):
        """
        Function to validate the required input of post method

        :param param: It can take one of the values from required param of post method
        :param value: Value of the passed param
        :return: value if value passes the validation criteria for the given param
        :raises: ValidationError: if value doesn't pass the validation criteria for the given param
        """

        if param == 'username':
            if value is not None and type(value) == str and len(value) > 0:
                if User.objects.filter(username=value).exists():
                    raise ValidationError('Username already taken, please try with a different username')
                return value
            else:
                raise ValidationError('Invalid username, it can\'t be empty')

        elif param == 'password':
            if value is not None and type(value) == str and len(value) >= 8:
                return value
            else:
                raise ValidationError('Invalid Password, password should be at least 8 characters long')

        elif param == 'email':
            if value is not None and type(value) == str and len(value) > 0:
                try:
                    validate_email(value)
                except ValidationError:
                    raise ValidationError('Invalid Email')
                else:
                    if User.objects.filter(email=value).exists():
                        raise ValidationError('E-mail already in use, please try logging in instead')
                    return value
            else:
                raise ValidationError('Invalid Email')

        else:
            raise ValidationError('Invalid Input Param Passed')