How to extract data between two strings

[SriMekala]

Hi,
I have input data as below,
input.xlsx:

Group	 Name	                  Rank
Group1	 ABC_YJK_02_S_2019-08-01	2
	     ABC_YMK_5_S_2019-08-01	    5
	     ABC_JKL_S_2019-08-04	    10
Group2	 BCA_POL_S_2019-08-01	    4
	     BCA_PAL_S_2019-08-01	    5
	     BCA_TYP_S_2019-08-01	    50
	     BCA_DIST_S_2019-08-01	    23
	     BCA_STA_S_2019-08-01	    3

I name column, I only want to delete everything before the first _(underline) including underline, and remove everything after _S including _S

Then I want to write the output into out.xlsx

I use the below code, but it is not working. giving below error:
TypeError: expected string or bytes-like object

import pandas as pd
import re

df = pd.read_excel('D:\pivotdata2.xlsx',sheetname='merge')
#df['Group']=df['Group'].fillna(method='ffill')

df.to_excel('D:\writepivotdata.xlsx',index=False) 

result=[]
for index, row in df.iterrows():
    result_tmp=re.search('_ (.*?)_',row)
    result.append(result_tmp)