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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 modify_site(name, sourcepath=None, apppool=None, preload=None):
    '''
    Modify a basic website in IIS.

    .. versionadded:: 2017.7.0

    Args:
        name (str): The IIS site name.
        sourcepath (str): The physical path of the IIS site.
        apppool (str): The name of the IIS application pool.
        preload (bool): Whether preloading should be enabled

    Returns:
        bool: True if successful, otherwise False.

    .. note::

        If an application pool is specified, and that application pool does not
        already exist, it will be created.

    CLI Example:

    .. code-block:: bash

        salt '*' win_iis.modify_site name='My Test Site' sourcepath='c:\\new_path' apppool='NewTestPool' preload=True
    '''
    site_path = r'IIS:\Sites\{0}'.format(name)
    current_sites = list_sites()

    if name not in current_sites:
        log.debug("Site '%s' not defined.", name)
        return False

    ps_cmd = list()

    if sourcepath:
        ps_cmd.extend(['Set-ItemProperty',
                       '-Path', r"'{0}'".format(site_path),
                       '-Name', 'PhysicalPath',
                       '-Value', r"'{0}'".format(sourcepath)])

    if apppool:

        if apppool in list_apppools():
            log.debug('Utilizing pre-existing application pool: %s', apppool)
        else:
            log.debug('Application pool will be created: %s', apppool)
            create_apppool(apppool)

        # If ps_cmd isn't empty, we need to add a semi-colon to run two commands
        if ps_cmd:
            ps_cmd.append(';')

        ps_cmd.extend(['Set-ItemProperty',
                       '-Path', r"'{0}'".format(site_path),
                       '-Name', 'ApplicationPool',
                       '-Value', r"'{0}'".format(apppool)])

    if preload:
        ps_cmd.extend(['Set-ItemProperty',
                       '-Path', "'{0}'".format(site_path),
                       '-Name', 'applicationDefaults.preloadEnabled',
                       '-Value', "{0};".format(preload)])

    cmd_ret = _srvmgr(ps_cmd)

    if cmd_ret['retcode'] != 0:
        msg = 'Unable to modify site: {0}\nError: {1}' \
              ''.format(name, cmd_ret['stderr'])
        raise CommandExecutionError(msg)

    log.debug('Site modified successfully: %s', name)
    return True