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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