collections.UserString can take away a lot of this boilerplate pain from user defined str subclasses. On Sun, Dec 18, 2022 at 7:28 PM Steven D'Aprano <steve@pearwood.info> wrote:
On Sun, Dec 18, 2022 at 07:38:06PM -0500, David Mertz, Ph.D. wrote:
However, if you want to allow these types to possibly *do* something with the strings inside (validate them, canonicalize them, do a security check, etc), I think I like the other way:
#2
class html(str): pass class css(str): pass
The problem with this is that the builtins are positively hostile to subclassing. The issue is demonstrated with this toy example:
class mystr(str): def method(self): return 1234
s = mystr("hello") print(s.method()) # This is fine. print(s.upper().method()) # This is not.
To be useable, we have to override every string method that returns a string. Including dunders. So your class becomes full of tedious boiler plate:
def upper(self): return type(self)(super().upper()) def lower(self): return type(self)(super().lower()) def casefold(self): return type(self)(super().casefold()) # Plus another 29 or so methods
This is not just tedious and error-prone, but it is inefficient: calling super returns a regular string, which then has to be copied as a subclassed string and the original garbage collected.
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