Панды чтение CSV Укажите DTYPE столбца
import pandas as pd
import numpy as np
data = '''\
1,2,3
4,5,6'''
fileobj = pd.compat.StringIO(data)
df = pd.read_csv(fileobj, dtype={0:'int8',1:'int8',2:'int32'}, header=None)
print(df.dtypes)
Real Raccoon