当参数在方括号中时，文档中的含义是什么？

Question

When I'm reading documentation I don't understand what it means when function parameters are in square brackets.

Taking for example OpenCV's GaussianBlur function:

cv2.GaussianBlur(src, ksize, sigmaX[, dst[, sigmaY[, borderType]]]) → dst

What do the square brackets just after sigmaX , mean?

Answer 1

It means optional arguments.

It is not python specific syntax, it is more general grammar notation syntax, for example, fromhttps://en.wikipedia.org/wiki/Extended_Backus–Naur_form :

Many BNF specifications found online today are intended to be human-readable and are non-formal. These often include many of the following syntax rules and extensions:

Optional items enclosed in square brackets: [].

Better explanation inhttps://en.wikipedia.org/wiki/Extended_Backus–Naur_form , Basics chapter.