It would be best to discuss this on comp.lang.python or python-ideas to get general support for the idea before trying to bring this to python-dev in hopes of changing people's minds.
On Fri, Aug 14, 2009 at 11:39, Jason R. Coombs <jar...@jaraco.com> wrote: > I’d like to express additional interest in python patch 1660179, > discussed here: > > > > http://mail.python.org/pipermail/patches/2007-February/021687.html > > > > On several occasions, I’ve had the desire for something like this. I’ve > made due with lambda functions, but as was mentioned, the lambda is clumsy > and harder to read than functools.compose would be. > > > > A potentially common use-case is when a library has a multi-decorator use > case in which they want to compose a meta decorator out of one or more > individual decorators. > > > > Consider the hypothetical library. > > > > # we have three decorators we use commonly > > def dec_register_function_for_x(func): > > # do something with func > > return func > > > > def dec_alter_docstring(func): > > # do something to func.__doc__ > > return func > > > > def inject_some_data(data): > > def dec_inject_data(func): > > func.data = data # this may not be legal, > but assume it does something useful > > return func > > return dec_inject_data > > > > # we could use these decorators explicitly throughout our project > > @dec_register_function_for_x > > @dec_alter_docstring > > @dec_inject_some_data(‘foo data 1’) > > def our_func_1(params): > > pass > > > > @dec_register_function_for_x > > @dec_alter_docstring > > @dec_inject_some_data(‘foo data 2’) > > def our_func_2(params): > > pass > > > > For two functions, that’s not too onerous, but if it’s used throughout the > application, it would be nice to abstract the collection of decorators. One > could do this with lambdas. > > > > def meta_decorator(data): > > return lambda func: > dec_register_function_for_x(dec_alter_docstring(dec_inject_some_data(data)(func))) > > > > But to me, a compose function is much easier to read and much more > consistent with the decorator usage syntax itself. > > > > def meta_decorator(data): > > return compose(dec_register_function_for_x, dec_alter_docstring, > dec_inject_some_data(data)) > > > > The latter implementation seems much more readable and elegant. One > doesn’t even need to know the decorator signature to effectively compose > meta_decorators. > > > > I’ve heard it said that Python is not a functional language, but if that > were really the case, then functools would not exist. In addition to the > example described above, I’ve had multiple occasions where having a general > purpose function composition function would have simplified the > implementation by providing a basic functional construct. While Python isn’t > primarily a functional language, it does have some functional constructs, > and this is one of the features that makes Python so versatile; one can > program functionally, procedurally, or in an object-oriented way, all within > the same language. > > > > I admit, I may be a bit biased; my first formal programming course was > taught in Scheme. > > > > Nevertheless, I believe functools is the ideal location for a very basic > and general capability such as composition. > > > > I realize this patch was rejected, but I’d like to propose reviving the > patch and incorporating it into functools. > > > > Regards, > > Jason > > _______________________________________________ > 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/brett%40python.org > >
_______________________________________________ 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
