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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(where='.', exclude=(), invalidate_cache=False):
 """ This version of ``find_packages`` caches previous results to speed up subsequent calls. Use ``invalide_cache=True`` to ignore cached results from previous ``find_packages`` calls, and repeat the package search. """


    if exclude:
        warnings.warn(
            "Use of the exclude parameter is no longer supported since it does "
            "not work as expected. Use add_exclude_packages instead. Note that "
            "it must be called prior to any other calls from setup helpers.",
            AstropyDeprecationWarning)

    # Calling add_exclude_packages after this point will have no effect
    _module_state['excludes_too_late'] = True

    if not invalidate_cache and _module_state['package_cache'] is not None:
        return _module_state['package_cache']

    packages = _find_packages(
        where=where, exclude=list(_module_state['exclude_packages']))
    _module_state['package_cache'] = packages

    return packages