How do you change French nouns from masculine to feminine?

When it is possible to do so (not all French nouns can be changed from masculine to feminine or vice-versa), the mark of the feminine is often an additional "e" at the end of the Word.

Ex: un étudiant, une étudiante - le boulanger, la boulangère (the baker); le gagnant, la gagnante (the winner); un français, une française (a Frenchman, a Frenchwoman).

But that has many many exceptions:

- Words which are used in one gender only : une hironDELLe (a swallow) is a feminine Word even when it is the male bird; le moineau (the sparrow) is a masculine noun even when speaking of the female bird.

- Words which are spelled the same in both genders: un peintre, une peintre (a painter); un juge, une juge (a judge)

- Words which are commonly spelled the same in both genders: un professeur, une professeur (a teacher); un auteur, une auteur (a writer) but are increasingly "feminized" by an additional "e" (une professeure, une auteure). These new spellings are now accepted as correct, but look quite awful to most people.