It's easy to forget the `esc` function. How does the recipient check (or type check) that it was called in all the right places?

Most DBs support parameterized queries which can be cached for performance. How do you pick out the parameters from that and replace those parts of the strings with the DB's parameter placeholders?

    t'Select * from {table} where name = {name}'

Looks very similar, but execution engine has access to all the individual parts, making it very easy to add placeholders such as:

    ('Select * from ? where name = ?`, table, name)

Or even (if the DB supports it), has access to the expressions inside the string and can use named parameters:

    ('Select * from @table where name = @name', { "table": table, "name": name })

That's really nice for debugging, depending on your DB engine.

In every DB engine that supports it, parameterized SQL is even safer than escape syntaxes because parameters are passed in entirely different parts of the binary protocols and don't need to rely on just string manipulation to add escape sequences.

While your code is a valid alternative way to implement @haberman's description, the feature is actually much more flexible.

The "subsequent logic" has full access to the interpolation results and strings. Not only can it escape the results, it can do whatever it wants to them. It can also do whatever it wants to the strings, and then combine everything in any way it likes - it's not even necessary that the final result is a string.

The other PEP example shows generating HTML attributes from a passed-in dictionary. HTML has a number of places where this is helpful, if you have original data.