[Python-Dev] Issue #26204: compiler now emits a SyntaxWarning on constant statement (original) (raw)

Gregory P. Smith greg at krypto.org
Mon Feb 8 13:06:17 EST 2016

On Mon, Feb 8, 2016 at 9:44 AM Victor Stinner <victor.stinner at gmail.com> wrote:

Hi,

I changed the Python compiler to ignore any kind "constant expressions", whereas it only ignored strings and integers before: http://bugs.python.org/issue26204 The compiler now also emits a SyntaxWarning on such case. IMHO the warning can help to detect bugs for developers who just learnt Python. The warning is not emited for strings, since triple quoted strings are a common syntax for multiline comments. The warning is not emited neither for ellispis (...) since "f(): ..." is a legit syntax for abstract function. Are you ok with the new warning?

I'm +1 on this.

-gps

New behaviour: haypo at smithers$ ./python Python 3.6.0a0 (default:759a975e1230, Feb 8 2016, 18:21:23) >>> def f(): ... False ... :2: SyntaxWarning: ignore constant statement >>> import dis; dis.dis(f) 2 0 LOADCONST 0 (None) 3 RETURNVALUE Old behaviour: haypo at smithers$ python3 Python 3.4.3 (default, Jun 29 2015, 12:16:01) >>> def f(): ... False ... >>> import dis; dis.dis(f) 2 0 LOADCONST 1 (False) 3 POPTOP 4 LOADCONST 0 (None) 7 RETURNVALUE

Before strings and numbers were already ignored. Example: haypo at smithers$ python3 Python 3.4.3 (default, Jun 29 2015, 12:16:01) >>> def f(): ... 123 ... >>> import dis; dis.dis(f) 2 0 LOADCONST 0 (None) 3 RETURNVALUE Victor

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