New submission from Xinmeng Xia <xi...@smail.nju.edu.cn>:
In full grammar specification of Python 3.6 official documentation (Python 3.6 official documentation: https://docs.python.org/3.6/reference/grammar.html ), we can find a very clear definition on the grammar about the usage of 'break'. According to the definition, we can find the following derivation, which indicates the keyword 'break' can appear in the block of if statement without being nested into a loop block: %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% # Start symbols for the grammar: # single_input is a single interactive statement; single_input: NEWLINE | simple_stmt | compound_stmt NEWLINE compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated | async_stmt if_stmt: 'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite] suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT simple_stmt: small_stmt (';' small_stmt)* [';'] NEWLINE small_stmt: (expr_stmt | del_stmt | pass_stmt | flow_stmt | import_stmt | global_stmt | nonlocal_stmt | assert_stmt) flow_stmt: break_stmt | continue_stmt | return_stmt | raise_stmt | yield_stmt break_stmt: 'break' %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% However, the implementation of the Python parser requires the 'break' can only be embedded into a loop statement. See the following example: Example A(without loop): >>> compile("if True:break",'','exec') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "", line 1 SyntaxError: 'break' outside loop Example B(with a loop): >>> compile("while True:\n\tif True:break",'','exec') <code object <module> at 0x7f5f4de90b70, file "", line 1> Similar problems exist between if-statement and keywords: 'continue', 'yield', 'return', 'nonlocal' in Python 3.6 and later versions. ---------- assignee: docs@python components: Documentation messages: 380502 nosy: docs@python, xxm priority: normal severity: normal status: open title: The grammar specification is inconsistent with the implementation of Python parser. type: compile error versions: Python 3.6 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue42284> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
