(original) (raw)

How to resolve distinguishing between documentation and implementation
if current implementation is incorrect, but third-party code can
implicitly depends on it?

For example see issue26198\. Currently buffer overflow of predefined
buffer for "es#" and "et#" format units causes TypeError (with
misleading message, but this is other story). The correct and
\*documented\* exception is ValueError. User code can depend on current
behavior, because TypeError is what is raised now for this type of
errors, and this is what is raised for other types of errors. Unlikely
authors of such code read the documentation, otherwise this issue would
be reported earlier. On other hand, looks these format units are rarely
used with predefined buffer (never in the stdlib since 3.5).

I think it is obvious that the code in the development branch should be
changed to produce documented and more logical exception. But what about
bugfix releases? Changing the documentation would be misleading,
changing the code can break existing code (unlikely, but).