Before-the-dot-in-a-file-name, what is it called

Here's how to do it with the # and % operators in Bash.

$ x="/foo/fizzbuzz.bar"
$ y=${x%.bar}
$ echo ${y##*/}
fizzbuzz

${x%.bar} could also be ${x%.*} to remove everything after a dot or ${x%%.*} to remove everything after the first dot.

Example:

$ x="/foo/fizzbuzz.bar.quux"
$ y=${x%.*}
$ echo $y
/foo/fizzbuzz.bar
$ y=${x%%.*}
$ echo $y
/foo/fizzbuzz

Documentation can be found in the Bash manual. Look for ${parameter%word} and ${parameter%%word} trailing portion matching section.

Yes. Use os.path.splitext(see Python 2.X documentation or Python 3.X documentation):

>>> import os
>>> filename, file_extension = os.path.splitext('/path/to/somefile.ext')
>>> filename
'/path/to/somefile'
>>> file_extension
'.ext'

Unlike most manual string-splitting attempts, os.path.splitext will correctly treat /a/b.c/d as having no extension instead of having extension .c/d, and it will treat .bashrc as having no extension instead of having extension .bashrc:

>>> os.path.splitext('/a/b.c/d')
('/a/b.c/d', '')
>>> os.path.splitext('.bashrc')
('.bashrc', '')