df[[column_name]].astype(int)
# convert Series
my_series = pd.to_numeric(my_series)
# convert column "a" of a DataFrame
df["a"] = pd.to_numeric(df["a"])
my_series = pd.to_numeric(my_series)
# convert column "a" of a DataFrame
df["a"] = pd.to_numeric(df["a"])
df[[column_name]].astype(int)
df["col-1"] = pd.to_numeric(df["col-1"])