[Python-ideas] Runtime assertion with no overhead when not active

[Michel Desmoulin]

Maybe somebody already answered this, but what's the difference between
this and the keyword "assert", which basically can be stripped of using
"python -o" ?

Le 05/05/2018 à 10:04, Eloi Gaudry a écrit :
> 
>     Hi folks,
> 
> 
>     I intend to add a runtime assertion feature in python. Before
>     submitting a PEP, I am sending a draft to this mailing list to
>     discuss whether it would make sense (above this message). I have
>     actually been using it for the last 2 years and it has proven to be
>     robust and has achieved its primary goal.
> 
> 
>     Briefly, the idea is to add a new assert that can be switch on/off
>     depending on some variable/mechanism at runtime. The whole point of
>     this assert is that it should not bring any overhead when off, i.e.
>     by avoiding evaluating the expression enclosed in the runtime
>     assert. It thus relies on Python grammar.
> 
> 
>     Thanks for your feedback.
> 
> 
>     Eloi
> 
> 
>      
> 
> 
>      
> 
> 
>      
> 
> 
>     Abstract
> 
> This PEP aims at offering a runtime assert functionnality, extending the
> compiletime assert already available.
> 
> 
>     Rationale
> 
> There is no runtime assert relying on python grammar available. For
> diagnostics and/or debugging reasons, it would be valuable to add such a
> feature.
> 
> A runtime assert makes sense when extra checks would be needed in a
> production environment (where non-debug builds are used).
> 
> By extending the current python grammar, it would be possible to limit
> the overhead induces by those runtime asserts when running in a non
> "assertive" mode (-ed). The idea here is to avoid evaluating the
> expression when runtime assertion is not active.
> 
> A brief example why avoiding evaluating the expression is needed to
> avoid any overhead in case the runtime assert should be ignored.
> 
> ::
> 
> runtime_assert( 999 in { i:None for i in range( 10000000 ) } )
> 
> 
>     Usage
> 
> ::
> 
> runtime_assert( expr )
> 
> #would result in if expr and runtime_assert_active:
> 
> print RuntimeAssertionError()
> 
> 
>     Implementation details
> 
> There is already an implementation available, robust enough for
> production. The implementation is mainly grammar based, and thus the
> parser and the grammar needs to be updated:
> 
>   * Python/graminit.c
>   * Python/ast.c
>   * Python/symtable.c
>   * Python/compile.c
>   * Python/Python-ast.c
>   * Python/sysmodule.c
>   * Modules/parsermodule.c
>   * Include/Python-ast.h
>   * Include/graminit.h
>   * Include/pydebug.h
>   * Grammar/Grammar
>   * Parser/Python.asdl
>   * Lib/lib2to3/Grammar.txt
>   * Lib/compiler/ast.py
>   * Lib/compiler/pycodegen.py
>   * Lib/compiler/transformer.py
>   * Lib/symbol.py
>   * Modules/parsermodule.c
> 
> 
>     References
> 
> [1]
> 
> 	
> 
> PEP 306, How to Change Python's Grammar
> (http://www.python.org/dev/peps/pep-0306)
> 
> 
>     Copyright
> 
> This document has been placed in the public domain.
> 
>  
> 
> 
> 
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