python how to find difference between two values

[hare]

Need help in giving me an idea on how to get the output

I am new to python.
My input is like this:

Output:
M <01/14/2019 08:07:01> Count:0	Total:50	Free: 20	A	B M <01/14/2019 08:07:04> Count:1	Total:5	Free:10	A	B M <01/14/2019 08:07:07> Count:2	Total:5	Free:3	A	B

I am trying to make a output like where it prints the free and then the difference between the current free and previous free

Output:
M <01/14/2019 08:07:01> Count:0 Free: 20	M <01/14/2019 08:07:04> Count:1 Free: 10 absolute difference between time and prev time is -10	M <01/14/2019 08:07:07> Count:2 Free: 3 absolute difference between time and prev time is -7	.

And then later on i need to determine the time when we had the most negative free value.


I tried a code like this
Which printed

 with open("summ4.txt") as f:	# get first line/number	nxt = int(next(f))	for n in f:	print("absolute difference between {} and {} = {}" .format(n.rstrip(), nxt, abs(int(nxt) - int(n))))	# set nxt equal to the next number	nxt = int(next(f,0)) a=open('summ1.txt','r').readlines() b=open('summ3.txt','r').readlines()	with open('summ.txt','w') as out: for i in range(0,365): print>>out,a[i].rstrip(),b[i]

.
i hit

Error:
Traceback (most recent call last):	File "3.py", line 39, in <module> .format(n.rstrip(), nxt, abs(int(nxt) - int(n))))	ValueError: zero length field name in format 

.
I guess my input file has a tab in the start and not able to get a difference rightly.
.
Any pointers on how to achieve the desired result?

Thanks,
Hare

[Gribouillis]

It seems that you are using an old version of python, isn't that the problem?