%0 Journal Article %T Specifying the Behaviour of Python Programs: Language and Basic Examples %J The Python Papers %D 2010 %I The Python Papers Anthology %X This manuscript describe BeSSY, a function-centric language for formal behavioural specification that requires no more than high-school mathematics on arithmetic, functions, Boolean algebra and sets theory. An object can be modelled as a union of data sets and functions whereas inherited object can be modelled as a union of supersets and a set of object-specific functions. Python list and dictionary operations will be specified in BeSSY for illustration. %U http://ojs.pythonpapers.org/index.php/tpp/article/view/138