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"Data blocks" syntax specification draft

Christian Gollwitzer <auriocus at gmx.de>:

> I'd think that the definitive answer is in the grammar, because that is
> what is used to build the Python parser:
> 	https://docs.python.org/3/reference/grammar.html
> Actually, I'm a bit surprised that tuple, list etc. does not appear
> there as a non-terminal. It is a bit hard to find, and it seems that
> "atom:" is the starting point for parsing tuples, lists etc.

testlist and testlist_comp are the interesting entities.

The syntax definition does not help you understand the semantics. For
example, omitting yield_expr and testlist_comp in

   atom: ('(' [yield_expr|testlist_comp] ')' |

evaluates to a tuple and nothing in

   testlist: test (',' test)* [',']

suggests what effect the the presence or absence of the final ',' could
have on the evaluation.