[Python-Dev] (#19562) Asserts in Python stdlib code (datetime.py) (original) (raw)

Jan Kaliszewski zuo at chopin.edu.pl
Mon Nov 18 03:34:50 CET 2013

17.11.2013 23:05, Guido van Rossum wrote:

The correct rule should be "don't use assert (the statement) to check for valid user input" and the stated reason should be that the assert statement was designed to be disabled globally, not to be a shorthand for "if not X: raise (mumble) Y". A corollary should also be that unittests should not use the assert statement; some frameworks sadly encourage the anti-pattern of using it in tests.

My problem with -O (and -OO) is that even though my code is valid (in terms of the rule 'use assert only for should-never-happen cases') I have no control over 3rd party library code: I can never know whether doesn't it break if I turn -O or -OO on (as long as I do not analyze carefully the code of the libraries I use, including writing regression tests [for 3rd party code]...).

Woudln't it to be useful to add possibility to place an "optimisation cookie" (syntactically analogous to "encoding cookie") at the beginning of each of my source files (when I know they are "-O"-safe), e.g.:

 # -*- opt: asserts -*-

or even combined with an encoding cookie:

 # -*- coding: utf-8; opt: asserts, docstrings -*-

Then:

(Of course, the '-*-' fragments in the above examples are purely conventional; the actual regex would not include them as it does not include them now for encoding cookies.)

Cheers. *j

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