Problem:
Given tuples in the form (key, string), use 'key' to determine
what string method to apply to the string:
key operation
-----------------------
l lower()
u upper()
t title()
...
Commentary:
Easy, right? Well ... except that I would really, really like
to avoid cascading ifs or eval based solutions. I'd like to implement
this as a jump table dictionary:
jt = { 'l' : lower_function reference,
'u' : upper_function reference,
...
}
So I could then do this:
string = jt[key](string)
But There's A Problem:
I tried to do this:
jt = {'l', "".lower,
'u', "".upper,
...
}
You can get away with this because all string objects appear to point to
common
method objects. That is,: id("a".lower) == id("b".lower)
HOWEVER, you cannot then do this:
string = jt[key](string)
Why? Because the methods of a string, while common to all strings
*do not accept an arg*. They are implemented to "know" about the
string instance they "belong to" (that contains them).
(Forgive me here, I am probably not using some of the OO arcana properly...)
I realize that the string module has many of the same functions that
are found as methods on strings. But it doesn't have all of them -
the .title() method is notably absent. If this were not the case,
I could happily do things like 'l' : string.lower and my approach
would work fine.
Even if I could use the string module, I'd still be curious though:
How do you get a reference to a method found in one object instance, but
actually apply it to another instance of the same class? I'm guessing this
may
involve fiddling with some of the internal __ variables, but I'm not
quite sure where to go next.
As I said, I know I could do this as a set of cascading ifs or even as an
eval, but I'm loathe to use such approaches. I like jump tables as a
structural construct because they are easy to understand and maintain. I
also realize that what I'm asking may be violating some deeply held notion
of OO purity, but, well, now I'm just curious if there is a way to do this
...
------------------------------------------------------------------------
Tim Daneliuk
tun...@tundraware.com
--
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