import re
mainString = "[31m\n[1m[31mError: [0m[0m[1mError import KeyPair: InvalidKeyPair.Duplicate: The keypair 'avtx-ctrl-key' already exists.\n\tstatus code: 400, request id: a56bb69b-0dc1-4c2f-a0c0-96d1be7c1efe[0m\n\n[0m[0m[0m\n[31m\n[1m[31mError: [0m[0m[1mError"
start = r"Error:\s*(?:\[\d+m)+"
end   = r"(?=(?:\[\d+m)*\n\n)"
result = re.findall('%s(.*?)%s' % (start, end), mainString, re.S)
print(result)