Unlike most languages with interpolated strings, Python's formatted
string literals do not allow the nesting of quotes. For example,
this expression is not legal Python:
f"Foo {"bar"} baz"
If an interpolation requires quotes, those quotes nust differ from the
quotes used by the enclosing literal. We can fix the previous example
by rewriting it with single quotes:
f"Foo {'bar'} baz"
However, this presents a problem if there are more than two levels of
nesting, as Python only has two kinds of quotes (four if the outermost
string uses """ or '''): in this case, the expression becomes
unspellable, and must be assigned to a local that is then used in place
of the original expression. So this:
f"Foo {bar[f'index {baz["qux"]}']} zed"
becomes this:
index = "qux"
f"Foo {bar[f'index {baz[index]}']}"
To put it bluntly, Python code generation reqiures register allocation,
but for quotes. These changes implement exactly that.
These changes also include a fix for traversals that access values that
are dictionaries rather than objects, and must use indexers rather than
attributes.
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