[Python-Dev] The asciistr problem (original) (raw)

Greg Ewing greg.ewing at canterbury.ac.nz
Tue Jan 14 23:53:50 CET 2014

Guido van Rossum wrote:

I understand that '&' here stands for "any arbitrary combination", but what about searches? Given that asciistr's base class is str, won't it still blow up if you try to use it as an argument to e.g. bytes.startswith()? Equality tests also sound problematic; is b'x' == asciistr('x') == 'x' ???

I'm wondering whether asciistr shouldn't be a type at all, but just a function that constructs a string with the same type as another string.

All of these problems then go away. Instead of

foo.startswith(asciistr("prefix"))

you would write

foo.startswith(asciistr("prefix", foo))

There's also no chance of an asciistr escaping into the wild, because there's no such thing.

We probably want a more compact way of writing it, though. Ideally it would support currying. If we have a number of string literals in our function, we'd like to be able to write something like this at the top:

def myfunc(a):
   s = stringtype(a)
   ...

and then use s('foo') to construct all our string literals inside the function.

We could go further. If the function has more than one string argument, they're probably constrained to be of the same type, so in the interests of symmetry it would be nice if we could write

def myfunc(a, b):
   s = stringtype(a, b)
   ...

and have it raise a TypeError if a and b are not of the same string type.

-- Greg

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