<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def walk(self, pred=None, recursive=True):
 """Iterate over all target entries recursively. Args: pred (function, optional):
 Callback(:class:`ftpsync.resources._Resource`) should return `False` to ignore entry. Default: `None`. recursive (bool, optional):
 Pass `False` to generate top level entries only. Default: `True`. Yields: :class:`ftpsync.resources._Resource` """

        for entry in self.get_dir():
            if pred and pred(entry) is False:
                continue

            yield entry

            if recursive:
                if isinstance(entry, DirectoryEntry):
                    self.cwd(entry.name)
                    for e in self.walk(pred):
                        yield e
                    self.cwd("..")
        return