[$] Custom string formatters in Python

Python has hadformatted string literals(f-strings), a syntactic shorthand for buildingstrings, since 2015. Recently, Jim Baker, Guido van Rossum, and Paul Everitt haveproposedPEP 750 ("Tag Strings For Writing Domain-Specific Languages") which wouldgeneralize and expand that mechanism to provide Python library writers with additionalflexibility. Reactions to the proposed change were somewhat positive, althoughthere was a good deal of discussion of (and opposition to)the PEP's inclusion of lazy evaluation of template parameters.