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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 scan(self, folder, sub=None, next_=None):
 """ Request immediate rescan of a folder, or a specific path within a folder. Args: folder (str):
 Folder ID. sub (str):
 Path relative to the folder root. If sub is omitted the entire folder is scanned for changes, otherwise only the given path children are scanned. next_ (int):
 Delays Syncthing's automated rescan interval for a given amount of seconds. Returns: str """

        if not sub:
            sub = ''
        assert isinstance(sub, string_types)
        assert isinstance(next_, int) or next_ is None
        return self.post('scan', params={'folder': folder,
                                         'sub': sub,
                                         'next': next_})