How to use logger to print a list in just one line in Python

Question

I want to print a list using logging in only one line in Python 3.6. Currently my code looks like this.

logger = logging.getLogger()
logger.setLevel(log_level)
ch = logging.StreamHandler(sys.stdout)
ch.setLevel(log_level)
formatter = logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
ch.setFormatter(formatter)
logger.addHandler(ch)

# some codes in-between

num_list = [1, 2, 3, 4, 5]
logger.info("Numbers in num_list are: ")
for item in num_list:
    logger.info(item)

What I want to get is

2018-07-23 17:29:30,200 - root - INFO - Numbers in num_list are: 1 2 3 4 5

However, I would get

2018-07-23 17:29:30,200 - root - INFO - Numbers in num_list are:
2018-07-23 17:29:30,200 - root - INFO - 1
2018-07-23 17:29:30,200 - root - INFO - 2
2018-07-23 17:29:30,200 - root - INFO - 3
2018-07-23 17:29:30,200 - root - INFO - 4
2018-07-23 17:29:30,200 - root - INFO - 5

I know if I used print to output, I could have use print(item, end=" ") to explicitly change what follows the output. However, it seems that the logging won't accept end as an input parameter.

Does anyone have any ideas how I could get the desired output? Many thanks!

Answer 1

You are using a for loop which iterates over all of your list and logs it one by one try: logger.info("Numbers in num_list are: {}".format(' '.join(map(str, num_list)))) to post them all in once

See: https://docs.python.org/3/library/stdtypes.html?highlight=str#str.join

Answer 2

There is a strong difference between an output stream (used by print) and a message log. The stream is a sequence of characters (or bytes for binary strings) that may happen to contain newline characters. Those newlines characters are then interpreted when you display them on a terminal (or when you print them).

A log is a sequence of messages, and each message is supposed to be atomic. Once a message has been logged, you cannot add anything to it but can only log new messages.

So you have to first fully build your message and then log it:

num_list = [1, 2, 3, 4, 5]
msg = "Numbers in num_list are: " + " ".join(num_list)      # fully build the message
logger.info(msg)                                            #  and then log it