On Friday 31 July 2009 21:55:11 Terry Reedy wrote: > Emmanuel Surleau wrote: > >> Beyond the mutable/hashable distinction, there is an important > >> philosophical distinction articulated by Guido. He deems tuples to > >> be useful for struct like groupings of non-homogenous fields and > >> lists to be useful for sequences of homogenous data suitable for > >> looping. > > I think the use of the with 'homegeneous' in this context is wrong > because 1) it is ambiguous or even sometimes not the case, and 2) it > misleads. Everything is an object, so all collections are in that sense > homogeneous. If the meaning is restricted to type(ob), than a list > 'mixing' ints and floats would be non-homogeneous and not 'legitimate', > but Guido does not really mean that. > > The word tuple comes from relational databases as a generalization of > single, double, triple, quadruple, quintuple, sextuple, sestuple, > octuple, etc. A tuple is a data record with a fixed number of fields > with individual meaning. There is nothing about homogeneity of data type > in that definition. A triple of floats is legitimately a tuple when each > is a coordinate (the individual meanings). In other contexts, the same > triple might properly be a list (such as of heights of people > arbitrarily ordered).
My understanding is that, in this context, it's not so much data types which are heterogeneous, but the semantic meaning of the data. For instance, a tuple containing (first_name, last_name, address) would be a "legitimate" tuple, but not a tuple containing (address, address, address), which, if we follow Guido's philosophy, ought to be represented as a list. Whether including the distinction in the language offers any practical benefit is questionable. [snip] > > This would tend to show that Guido's notion here was not particularly > > intuitive. > > The problem is that it *is* intuitive, on his part, and usually not well > explained rationally. Excellent point. Cheers, Emm -- http://mail.python.org/mailman/listinfo/python-list
