best practices for writing to a file from multiple methods

Question

I have a class that contains a bunch of methods for checking data I scrape every week (for things like well-formedness and other errors in gathering the data). Each of these methods performs a test, and then prints out a summary of the test.

I want to print out the output from these tests to a file, but I'm not sure what the best way to do it is. For example...

• Should the class hold an instance variable to the file, and each method open/appends/closes the file? (A problem is that methods sometimes call other methods, so this seems kinda messy?)
• Should each method get passed the file as a parameter? (Seems messy as well.)
• Should each method return a string, and a"central" method that calls all the other tests outputs all these strings to a file?

I'm not really familiar with using logger libraries -- would that be a solution?

My particular context

I have a scraper that pulls data from various websites and stores them in a database. Websites change all the time, so I'm writing a "scrape checker" program that checks my scrapes for various things, like:

• number of empty results
• length of results
• weird characters in results
• and so on

So I have methods like:

• check_num_empty_results
• check_weird_characters
• check_scrape (calls a bunch of other checks)
• check_scrape_pair (sometimes I want to check pairs of scrapes together, e.g., to match results against each other, so this is different checking each one in isolation)
• etc.

I want my "scrape checker" program to print out a file that summarizes all the checks.

Answer 1

Separation of concerns. Write code the focuses on the scraping activity and return the value(s) scraped. Then use aspect oriented programming for logging, which can simplify the problem greatly as the aspect holds the reference to the file or logging API.

Answer 2

Seems like a logging framework would be a perfect solution for this. If you are using Java or .NET, log4j and log4net are pretty much the de-facto standards for that.

Answer 3

Ultimately, it depends on what language you're using.

The first solution makes the most sense if your language permits it. For each instance of the logging class, have a field for the file object that you're reading from/writing to. This is basically equivalent to passing the file object as a parameter to every method.

That said, most mature languages have modules that will do a lot of this work for you; off the top of my sh/awk, Perl, and Python all come to mind as being suited to this task (though if you want to, you could use Java or something else).