On 2009-06-09 17:06, Carl Banks wrote:
On Jun 9, 12:42 pm, Terry Reedy<tjre...@udel.edu> wrote:
Hendrik van Rooyen wrote:
I should have known - you use a string method to get a list of words,
but you have to go to the list to get a list of characters from a string.
That is symmetry.
There is no string method to do it, which is what I am complaining
about.
That would be asymmetry.
Is there a reason for this, or is the lack of symmetry just an historical
artefact?
A lack of perception to see the symmetry that is there.
Classes create instances of the class when called.
Sometimes alternate constructors are needed when there is more than one
possible way to create an instance from a given input. In the case of
str(iterable), one could want either a string representing the iterable
itself, just as with non-iterables, or a string representing the
concatenated contents of the iterable. Str.join implements the second
choice, with an added string parameter to allow a constant string to be
interpolated between the joined items.
But then how do you rationalize str.split(), which is a method of str
but a constructor of list?
There is a difference between a "constructor of a type" and just "a method that
returns a particular type". str.join() and str.split() are really examples of
the latter.
Perhaps instead of worrying about symmetry all the time we should just
accept the inevitability that things will always be asymmetric and
impure from someone's perspective. Terry's symmetry is Hendrik's
asymmetry and vice versa.
There is much wisdom in this.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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