def get_environ(self, key, default=None, cast=None):
        """Get value from environment variable using os.environ.get

        :param key: The name of the setting value, will always be upper case
        :param default: In case of not found it will be returned
        :param cast: Should cast in to @int, @float, @bool or @json ?
         or cast must be true to use cast inference
        :return: The value if found, default or None
        """
        key = upperfy(key)
        data = self.environ.get(key, default)
        if data:
            if cast in converters:
                data = apply_converter(cast, data, box_settings=self)
            elif cast is True:
                data = parse_conf_data(
                    boolean_fix(data), tomlfy=True, box_settings=self
                )
        return data
Get value from environment variable using os.environ.get

        :param key: The name of the setting value, will always be upper case
        :param default: In case of not found it will be returned
        :param cast: Should cast in to @int, @float, @bool or @json ?
         or cast must be true to use cast inference
        :return: The value if found, default or None
        
dynaconf/base.py