> > While I'm at it, why not propose that for py3k that > > .rfind/.rindex/.rjust/.rsplit disappear, and .find/.index/.just/.split > grow an > > optional "fromright" (or equivalent) optional keyword argument? > > This violates one of my design principles: don't add boolean options > to an API that control the semantics in such a way that the option > value is (nearly) always a constant. Instead, provide two different > method names. > > The motivation for this rule comes partly for performance: parameters > are relatively expensive, and you shouldn't make the method test > dynamically for a parameter value that is constant for the call site; > and partly from readability: don't bother the reader with having to > remember the full general functionality and how it is affected by the > various flags; also, a Boolean positional argument is a really poor > clue about its meaning, and it's easy to misremember the sense > reversed. > > PS. This is a special case of a stronger design principle: don't let > the *type* of the return value depend on the *value* of the arguments. > > PS2. As with all design principles, there are exceptions. But they > are, um, exceptional. index/rindex is not such an exception.
FWIW, after this is over, I'll put together a draft list of these principles. The one listed above has served us well. An early draft of itertools.ifilter() had an invert flag. The toolset improved when that was split to a separate function, ifilterfalse(). Other thoughts: Tim's rule on algorithm selection: We read Knuth so you don't have to. Raymond's rule on language proposals: Assertions that construct X is better than an existing construct Y should be backed up by a variety of side-by-side comparisons using real-world code samples. I'm sure there are plenty more if these in the archives. Raymond _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
