python grammar: wrong atom definition?

Question

While checking python grammar at official documentation, here is what it reads

atom_expr: ['await'] atom trailer*
atom: ('(' [yield_expr|testlist_comp] ')' |
       '[' [testlist_comp] ']' |
       '{' [dictorsetmaker] '}' |
       NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False')
testlist_comp: (test|star_expr) ( comp_for | (',' (test|star_expr))* [','] )
trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME

Then, 10.bit_length() is a valid syntax according to that definition but not according to the python interpreter. Instead, n=10;n.bit_length() is valid syntax for both the specifications and the interpreter.

Where should I find the real definition of atom and atom_expr?

interesting. a related question: https://stackoverflow.com/questions/33054229/accessing-attributes-on-literals-work-on-all-types-but-not-int-why — juanpa.arrivillaga, Feb 22 '18 at 10:14
Also somewhat related: https://stackoverflow.com/q/31037609/1639625 — tobias_k, Feb 22 '18 at 11:27

score 2 · Answer 1 · answered Feb 22 '18 at 10:40

Thanks to juanpa's comment and the answers in the related question, it appears that the problem comes from 10.. The definition of NUMBER includes the dot such that 10.bit_length() is of kind NUMBER NAME trailer and not NUMBER '.' NAME trailer.

In order to obtain an atom_expr, one must separate the dot: both 10 .bit_length() and (10).bit_length() give the correct answer.

python grammar: wrong atom definition?

1 Answers1