import numpy as np
import pandas as pd

df = pd.DataFrame({'a': [7, 1, 5], 'b': ['3','2','1']}, dtype='object')

df

df.dtypes

a    object
b    object
dtype: object

df = df.infer_objects()

df.dtypes

a     int64
b    object
dtype: object

# You can see that dataype of column a is changed to int64.