如何从数据帧中具有字母数字值的列中删除除特定单词之外的所有单词？

import pandas as pd
import re

data = {'col1': ['apple', 'banana', '123', 'orange', '456'],
        'col2': ['cat', 'dog', '789', 'elephant', 'bird']}
df = pd.DataFrame(data)

def remove_words_except_specific(df, col_name, specific_word):
    pattern = r'\b(?!(?:{})\b)\w+\b'.format(specific_word)
    df[col_name] = df[col_name].apply(lambda x: re.sub(pattern, '', x))
    return df

df = remove_words_except_specific(df, 'col1', 'apple')