Well, since OP is learning python ...
$ python SCRIPT.py
TXT_file = 'TXT.txt'
CSV_file = 'CSV.csv'
OUT_file = 'OUTPUT.csv'
## From the TXT, create a list of domains you do not want to include in output
with open(TXT_file, 'r') as txt:
domain_to_be_removed_list = []
## for each domain in the TXT
## remove the return character at the end of line
## and add the domain to list domains-to-be-removed list
for domain in txt:
domain = domain.rstrip()
domain_to_be_removed_list.append(domain)
with open(OUT_file, 'w') as outfile:
with open(CSV_file, 'r') as csv:
## for each line in csv
## extract the csv domain
for line in csv:
csv_domain = line.split(';')[0]
## if csv domain is not in domains-to-be-removed list,
## then write that to outfile
if (not csv_domain in domain_to_be_removed_list):
outfile.write(line)