Pandas how can 'replace' work after 'loc'?

Question

I have tried many times, but seems the \'replace\' can NOT work well after use \'loc\'. For example I want to replace the \'conlumn_b\' with an regex for the row that the \'

Answer 1

I'm going to borrow from a recent answer of mine. This technique is a general purpose strategy for updating a dataframe in place:

df.update(
    df.loc[df['conlumn_a'] == 'apple', 'conlumn_b']
      .replace(r'^11$', 'XXX', regex=True)
)

df

  conlumn_a conlumn_b
0     apple       123
1    banana        11
2     apple       XXX
3    orange        33

Note that all I did was remove the inplace=True and instead wrapped it in the pd.DataFrame.update method.