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On Tue, 8 Sep 2015 at 10:26 Erik <python@lucidity.plus.com> wrote:

Hi.

I realise I'm coming late to the party on this, but I have a question
about something I don't think the PEP makes clear.

When is the bytecode for the embedded expressions created?

Is it when the source code is parsed, or at runtime when the f-string is
evaluated?

It's at compile time.

If the latter, then any process that works on bytecode (introspection
tools, peep-hole optimisers etc) will need work.

I understand that colorising editors and analysis tools which operate at
the source code level will need work, that's fair enough.

The PEP hints at things in this area in the "Specification", "Code
equivalence" and "Expression evaluation" sections, and my guess is that
it will (and should) happen during parsing, but I can't see where it
comes right out and says it.

It doesn't explicitly state it because it's inherent in the fact that it is implemented in bytecode which is created at compile time for Python source (typically when a module is imported, but can be when you call compile()).