At 12:42 PM 6/26/2010 +0900, Stephen J. Turnbull wrote:
What I'm saying here is that if bytes are the signal of validity, and
the stdlib functions preserve validity, then it's better to have the
stdlib functions object to unicode data as an argument. Compare the
alternative: it returns a unicode object which might get passed around
for a while before one of your functions receives it and identifies it
as unvalidated data.
I still don't follow, since passing in bytes should return
bytes. Returning unicode would be an error, in the case of a
"polymorphic" function (per Guido).
But you agree that there are better mechanisms for validation
(although not available in Python yet), so I don't see this as an
potential obstacle to polymorphism now.
Nope. I'm just saying that, given two bytestrings to url-join or
path join or whatever, a polymorph should hand back a
bytestring. This seems pretty uncontroversial.
> What I want is for the stdlib to create stringlike objects of a
> type determined by the types of the inputs --
In general this is a hard problem, though. Polymorphism, OK, one-way
tainting OK, but in general combining related types is pretty
arbitrary, and as in the encoded-bytes case, the result type often
varies depending on expectations of callers, not the types of the
data.
But the caller can enforce those expectations by passing in arguments
whose types do what they want in such cases, as long as the string
literals used by the function don't get to override the relevant
parts of the string protocol(s).
The idea that I'm proposing is that the basic string and byte types
should defer to "user-defined" string types for mixed type
operations, so that polymorphism of string-manipulation functions is
the *default* case, rather than a *special* case. This makes
tainting easier to implement, as well as optimizing and other special
cases (like my "source string w/file and line info", or a string with
font/formatting attributes).
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