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I think is better to pass the index of the start symbol into the list of dfas down to the grammar and use that when generating the parser input files.

Could you please clarify?

Could you please clarify?

Yup, make pgen generate it from the position of the initial symbol. The initial dfa symbol is placed in the grammar in:

https://github.com/python/cpython/blob/e12f56075edc5704c9cfbf69d268474328642fa3/Parser/pgen/pgen.py#L53

The value has to be the position of that symbol in the list of dfas. It will be 0 as single_input is always the first DFA in the list of dfas, but doing programmatically will protect in case the position changes in the future. Basically something on the lines of (for illustrative purposes):

change:

"0, {n_states}, states_{dfa_index},\n".format(

to

start_index = list(self.dfas.keys()).index(self.start)
"{start}, {n_states}, states_{dfa_index},\n".format(start=start_index

Now I see what you mean, but d_initial is not about the initial DFA of the grammar, it's about the initial state of a DFA: each DFA has its own d_initial, and they're all zeroes.

Now I see what you mean, but d_initial is not about the initial DFA of the grammar, it's about the initial state of a DFA: each DFA has its own d_initial, and they're all zeroes.

Oh, right! Sorry, I have mistaken this with the start rule in the old pgen:

But as you indicate, d_initial has been initialized always to 0:

@tyomitch Can you rebase to regenerate the graminit.c file.

@tyomitch Can you rebase to regenerate the graminit.c file.

Done!

Thanks @tyomitch for the contribution! :)