def is_installed(package_name, config, stamp_content=None):
    'Returns True if the given package is installed.'
    stamp = get_install_stamp(package_name, config)
    result = check_stamp(stamp, stamp_content)
    return result
Returns True if the given package is installed.
def is_installed(package_name, config, stamp_content=None):
    
    stamp = get_install_stamp(package_name, config)
    result = check_stamp(stamp, stamp_content)
    return result