Writing string to file results in one character per line

[buran]

Your original code:

def write_to_log(s):
	# open the file in append mode
	with open('/home/bs/NAS_2/projects/Raspberry_pi/Temperature/log.txt', 'a') as f:
		# write the line to the text file
		f.write('\n'.join(line));

Note that your function expects parameter s, but it is never used. You actually use line and your code sort of works, only because there is line variable in global scope.
As to the problem you face - when you use '\n'.join(some_string) new-line is inserted between each char of the string

>>> foo = 'spam'
>>> eggs = '\n'.join(foo)
>>> eggs
's\np\na\nm'
>>> print(eggs) # same would be if you write to file
s
p
a
m
>>>

def write_to_log(log_msg):
	# open the file in append mode
	with open('/home/bs/NAS_2/projects/Raspberry_pi/Temperature/log.txt', 'a') as f:
		# write the line to the text file
		f.write(f'{log_msg}\n')

Right now the log file is hardcoded in the function, but you can pass it as argument.