Add prefix to dataframe columns that match those names in a list
Use a comprehension:
columns_to_prefix = set(['fruit', 'colour', 'country'])
df.columns = [f"the_{c}" if c in columns_to_prefix else c for c in df.columns]
print(df)
# Output
the_fruit the_colour popularity the_country cost
0 Apple Green High UK 2
1 Berry Red High Spain 4