I am an experienced Python programmer, and I make utilities like this for my own day-to-day chores.
I recommend you drop the .xls/.xlm input requirement, and just take UTF8-encoded CSV text files as input. The spreadsheets can export to CSV, the core of the analysis work is parsing tabular data, and taking on the .xls and .xlm format just adds risk that the Python modules for those formats will have some bug that gets in the way.
I will deliver a single Python source file which runs as a command-line program. You give it two parameters, the name of an input file, and the number (1-12) of a month that you want to compare. It prints:
* Average hotel stays for November of every year, average hotel stays for every month of every year, November average as percentage of every-month average, and message "higher" or "lower" for November average relative to every-month average.
* Which month has fewest average stays for all years in data file.
* Which month has most average stays for all years in data file.
* When printing name of month, it will adopt the name in column B (which looks like Icelandic). Other messages will be in English.
* Output file will be in UTF-8 plain text, to standard out.
Input format:
* All lines before, and blank lines, discarded.
* First line after blank lines discarded.
* Second line after blank lines is interpreted as column headers, giving years.
* Following 12 lines are interpreted as months, month 1 (January) to month 12 (December)
* UTF8 CSV text.