如何将基于公共主键的 Pandas 数据框中的特定单元格替换为 Python 中的另一个数据框

I'm trying to code in Python after a hiatus of 4 years and facing difficulties in implementing my ideas. I have 2 large excel sheets consisting of more than 12k x 70 values, both have the same number of columns and column names. I've created a primary key for both the dataframes and now I want to compare values from the primary key of one sheet to primary key of another and when there's a match I want to replace certain values(not all) from the old sheet to the new.
eg df1:

A   B   C   D   E   F
1   2   3   4   5   6
7   8   9   10  11  12
13  14  15  16  17  18

DF2:

A   B   C   D   E   F
19  20  21  22  23  6
25  26  27  28  29  12  
31  32  33  34  35  19

当手术完成后，我需要它看起来像这样 DF1:

A   B   C   D   E   F
1   2   21  22  23  6
7   8   27  28  29  12  
13  14  15  16  17  18

列F是主键

我try 了下面的方法，但输出结果非常奇怪

for i in df2['F']:
    for j in df1['F']:
        if i==j:
            df1['D'] = df2['D'].astype(str)            
            df1['E'] = df2['E'].astype(str)
            df1['C'] = df2['C'].astype(str)