Creating a "error log" record based on a condition

I wrote the code below to basically check on a left join which fields did not have a match and create cpCheckIn in order to display those results. What I would like to do is then create a conditional statement that says, if that new dataframe (cpCheckIn) is NOT = 0 rows, then to create a new record in errorLog with the name of the process - let's say 'counterparty check' - and the date/time of the error.

import pandas as pd
import numpy as np

errorLog = pd.DataFrame(columns=['process', 'date/time'])

imports here of the data I need, but wanted to keep only the relevant code

Pos = pd.merge(Pos, 
               cpTrans, 
               how='left', 
               left_on='COUNTERPARTY', 
               right_on='ticker',
               indicator='cpCheck')

cpCheckIn = Pos[Pos.cpCheck != 'both']

cpCheckIn = cpCheckIn.filter(['Position',
                              'COUNTERPARTY',
                              'ticker',
                              'counterparty_name',
                              'cpCheck'])

I have been trouble coming up with a solution here and wonder if I'm thinking about this in the correct order of events. Any advice is much appreciated, thanks!