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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 _retrieve_config_xml(config_xml, saltenv):
    '''
    Helper to cache the config XML and raise a CommandExecutionError if we fail
    to do so. If we successfully cache the file, return the cached path.
    '''
    ret = __salt__['cp.cache_file'](config_xml, saltenv)

    if not ret:
        raise CommandExecutionError('Failed to retrieve {0}'.format(config_xml))

    return ret