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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_package_dirs(root_path):
 """ Find python package directories in directory `root_path` Parameters root_path : str Directory to search for package subdirectories Returns ------- package_sdirs : set Set of strings where each is a subdirectory of `root_path`, containing an ``__init__.py`` file. Paths prefixed by `root_path` """

    package_sdirs = set()
    for entry in os.listdir(root_path):
        fname = entry if root_path == '.' else pjoin(root_path, entry)
        if isdir(fname) and exists(pjoin(fname, '__init__.py')):
            package_sdirs.add(fname)
    return package_sdirs