BlockPy: $7$B$2\mathrm{.}6)$ File Size

Write a function calculate$\_$file$\_$size that consumes the name of a file as a string and returns an integer indicating how many characters long the file's contents is using the Count pattern $($you may not use the built$-$in len function$).$ Call your function on the files below to unit test. The rainfall file has$891$ characters, the names file has$1064$ characters, and the empty file has $0$ characters.