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

Victor Stinner victor.stinner at gmail.com
Mon Feb 8 12:44:19 EST 2016

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?

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 LOAD_CONST 0 (None) 3 RETURN_VALUE

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 LOAD_CONST 1 (False) 3 POP_TOP 4 LOAD_CONST 0 (None) 7 RETURN_VALUE

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 LOAD_CONST 0 (None) 3 RETURN_VALUE

Victor

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