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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def safe_format( self, format_string, param_dict=None, force_composite=False, attr_getter=None ):
 r""" Parser for advanced formatting. Unknown placeholders will be shown in the output eg ``{foo}``. Square brackets ``[]`` can be used. The content of them will be removed from the output if there is no valid placeholder contained within. They can also be nested. A pipe (vertical bar) ``|`` can be used to divide sections the first valid section only will be shown in the output. A backslash ``\`` can be used to escape a character eg ``\[`` will show ``[`` in the output. ``\?`` is special and is used to provide extra commands to the format string, example ``\?color=#FF00FF``. Multiple commands can be given using an ampersand ``&`` as a separator, example ``\?color=#FF00FF&show``. ``\?if=<placeholder>`` can be used to check if a placeholder exists. An exclamation mark ``!`` after the equals sign ``=`` can be used to negate the condition. ``\?if=<placeholder>=<value>`` can be used to determine if {<placeholder>} would be replaced with <value>. ``[]`` in <value> don't need to be escaped. ``{<placeholder>}`` will be converted, or removed if it is None or empty. Formatting can also be applied to the placeholder Eg ``{number:03.2f}``. example format_string: ``"[[{artist} - ]{title}]|{file}"`` This will show ``artist - title`` if artist is present, ``title`` if title but no artist, and ``file`` if file is present but not artist or title. param_dict is a dictionary of placeholders that will be substituted. If a placeholder is not in the dictionary then if the py3status module has an attribute with the same name then it will be used. .. note:: Added in version 3.3 Composites can be included in the param_dict. The result returned from this function can either be a string in the case of simple parsing or a Composite if more complex. If force_composite parameter is True a composite will always be returned. attr_getter is a function that will when called with an attribute name as a parameter will return a value. """

        try:
            return self._formatter.format(
                format_string,
                self._py3status_module,
                param_dict,
                force_composite=force_composite,
                attr_getter=attr_getter,
            )
        except Exception:
            self._report_exception(u"Invalid format `{}`".format(format_string))
            return "invalid format"