I tried to combine and sum 2 Excel by Python but when I used “for loop”, I found an error “unsupported operand type(s) for +: ‘float’ and ‘str'”

See my code below:

import pandas as pd
import os

os.getcwd() + '/projects'

all_bit = os.listdir(os.getcwd() + '/projects/Python_excel/Test_files')

#Read Excel Bitcoin 1
bitcoin1 = pd.read_excel(os.getcwd() + '/projects/Python_excel/Test_files/' + all_bit[0])

#Check file
all_bit[0]

#Change data types
bitcoin1["Latest"] = bitcoin1["Latest"].astype(int)
bitcoin1["Open"] = bitcoin1["Open"].astype(int)
bitcoin1["Highest"] = bitcoin1["Highest"].astype(int)
bitcoin1["Lowest"] = bitcoin1["Lowest"].astype(int)

#Drop unnecessary column
bitcoin1 = bitcoin1.drop(['%Change','Amount'], axis = 1, inplace = False)

#Read Excel Bitcoin 2
bitcoin2 = pd.read_excel(os.getcwd() + '/projects/Python_excel/Test_files/' + all_bit[1])

#Change data types
bitcoin2["Latest"] = bitcoin2["Latest"].astype(int)
bitcoin2["Open"] = bitcoin2["Open"].astype(int)
bitcoin2["Highest"] = bitcoin2["Highest"].astype(int)
bitcoin2["Lowest"] = bitcoin2["Lowest"].astype(int)

#Drop unnecessary column
bitcoin2 = bitcoin2.drop(['%Change','Amount'], axis = 1, inplace = False)

#Loop
rep = pd.DataFrame()
for bitcoin in all_bit:
    data_bit = pd.read_excel(os.getcwd() + '/projects/Python_excel/Test_files/' + bitcoin)
    rep = rep.add(data_bit.set_index('Date'),fill_value=0)

After I finished my for loop, it showed “TypeError: unsupported operand type(s) for +: ‘float’ and ‘str'”. I tried to change float to int but it not working.

Could you guys advice me?

Thank you