def conv(bstr):
out = bstr.decode('utf-8')
out_arr = out.split('\r\n')
out = [line for line in out_arr if line.strip()]
return '\r\n'.join(map(str, out))
b_test = '\r\nnan\r\n\r\nnan\r\n\r\n\r\nnan'
print ('Przed konwersją')
print (b_test)
print ('\nPo konwersji')
print (conv(bytes(b_test, 'utf-8')))