dataframe = dataframe.astype("float")

for _i, _value in dataframe.iteritems():
    dataframe.loc[:, _i] = pd.to_numeric(_value)

import pandas as pd
import numpy as np

dataframe = pd.DataFrame(np.random.random(size=(10, 5)))

RangeIndex: 10 entries, 0 to 9
Data columns (total 5 columns):
 #   Column  Non-Null Count  Dtype 
---  ------  --------------  ----- 
 0   0       10 non-null     object
 1   1       10 non-null     object
 2   2       10 non-null     object
 3   3       10 non-null     object
 4   4       10 non-null     object
dtypes: object(5)
memory usage: 528.0+ bytes