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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 _find_packages_iter(cls, where, exclude, include):
 """ All the packages found in 'where' that pass the 'include' filter, but not the 'exclude' filter. """

        for root, dirs, files in os.walk(where, followlinks=True):
            # Copy dirs to iterate over it, then empty dirs.
            all_dirs = dirs[:]
            dirs[:] = []

            for dir in all_dirs:
                full_path = os.path.join(root, dir)
                rel_path = os.path.relpath(full_path, where)
                package = rel_path.replace(os.path.sep, '.')

                # Skip directory trees that are not valid packages
                if ('.' in dir or not cls._looks_like_package(full_path)):
                    continue

                # Should this package be included?
                if include(package) and not exclude(package):
                    yield package

                # Keep searching subdirectories, as there may be more packages
                # down there, even if the parent was excluded.
                dirs.append(dir)