熊猫:将单元格值设置为当前行的索引?

将索引值转换为字符串并添加列 country :

df['d'] = (df.index + 1).astype(str) + '. ' + df['country']
print (df)
   a  b   c  country           d
0  5  7  11  Morocco  1. Morocco
1  5  9   9  Nigeria  2. Nigeria
2  6  2  13    Spain    3. Spain

另一个解决方案 python 3.6+ :

df['d'] = [f'{i + 1}. {x}' for i, x in enumerate(df['country'])]
#for versions below
#df['d'] = ['{}. {}'.format(i + 1, x) for i, x in enumerate(df['country'])]
print (df)
   a  b   c  country           d
0  5  7  11  Morocco  1. Morocco
1  5  9   9  Nigeria  2. Nigeria
2  6  2  13    Spain    3. Spain