Here's a solution with expl3:
\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\addbrackets}{ m }
{
\tarass_addbrackets:n { #1 }
}
\seq_new:N \l__tarass_addbrackets_seq
\cs_new_protected:Npn \tarass_addbrackets:n #1
{
\seq_set_split:Nnn \l__tarass_addbrackets_seq { ; } { #1 }
[\seq_use:Nn \l__tarass_addbrackets_seq {]~[}]
}
\ExplSyntaxOff
\begin{document}
\addbrackets{360;90;7,2}
\end{document}
Several refinements are possible.

If you're using the French module for babel, you have to be aware of the fact that ; is a special character, because of the peculiar French habit of having a space before the semicolon.
\documentclass{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[french]{babel}
\usepackage{xparse}
\ExplSyntaxOn
\shorthandon{;}
\NewDocumentCommand{\addbrackets}{ m }
{
\tarass_addbrackets:n { #1 }
}
\seq_new:N \l__tarass_addbrackets_seq
\cs_new_protected:Npn \tarass_addbrackets:n #1
{
\seq_set_split:Nnn \l__tarass_addbrackets_seq { ; } { #1 }
[\seq_use:Nn \l__tarass_addbrackets_seq {]~[}]
}
\shorthandoff{;}
\ExplSyntaxOff
\begin{document}
\addbrackets{360;90;7,2}
\end{document}
;separated list which has,in the items. (\{is a red herring) – David Carlisle Apr 28 '14 at 16:45