list1 = ['Contact: Hamdan Z Hamdan, MBBS, Msc',

'\r\n ',

'+249912468264',

'\r\n ',

'hamdanology@hotmail.com',

'\r\n ',

'Contact: Maha I Mohammed, MBBS, PhD',

'\r\n ',

'+249912230895',

'\r\n ',

'\r\n ',

'Sudan',

'Jaber abo aliz',

'\r\n ',

'Recruiting',

'\r\n ',

'Khartoum, Sudan, 1111 ',

u'Contact: Khaled H Bakheet, MD,PhD \xa0 \xa0 +249912957764 \xa0 \xa0 ',

'khalid2_3456@yahoo.com',

u' \xa0 \xa0 ',

u'Principal Investigator: Hamdan Z Hamdan, MBBS,MSc \xa0 \xa0 \xa0 \xa0 \xa0 \xa0 ',

'Principal Investigator:',

'\r\n ',

'Hamdan Z Hamdan, MBBS, MSc',

'\r\n ',

'Al-Neelain University',

'\r\n '

]

从这个字符串列表中，我只需要提取不应该与其他字符关联的4位整数？在

示例：“1111”是所需的输出。在

我们应该如何用python编写regex？显然，这行不通：*([\d]{4})*。在