只要您对pandas允许的df.loc[condition, column]语法感到满意，这很容易，只需执行df['col'] != 'pre'即可找到所有应进行更改:

As long as you're comfortable with the df.loc[condition, column] syntax that pandas allows, this is very easy, just do df['col'] != 'pre' to find all rows that should be changed:

df['col2'] = df['col']
df.loc[df['col'] != 'pre', 'col2'] = 'nonpre'

df
Out[7]: 
    col    col2
0   pre     pre
1  post  nonpre
2     a  nonpre
3     b  nonpre
4  post  nonpre
5   pre     pre
6   pre     pre