: dtypes를 통하여 각 column의 타입 살펴 봄,
pandas.Series.astype(str)
df["score"].astype(str)
df["score"].astype(int)
df["score"].astype(float)
출처: https://www.delftstack.com/ko/howto/python-pandas/how-to-convert-pandas-dataframe-column-to-string/