First you need to fond a core dev to sponsor you (Steven D’A?). That person will guide you through the process.
On Sat, Sep 25, 2021 at 08:30 Noam Tenne <n...@10ne.org> wrote: > So should I just scratch this and rewrite a PEP for an extensible > assertion mechanism? > > On Fri, Sep 24, 2021, at 14:04, Noam Tenne wrote: > > Hi All, > > Following the discussions on "Power Assertions: Is it PEP-able?", I've > drafted this PEP. > Your comments are most welcome. > > PEP: 9999 > Title: Power Assertion > Author: Noam Tenne <n...@10ne.org> > Status: Draft > Type: Standards Track > Content-Type: text/x-rst > Created: 24-Sep-2021 > > > Abstract > ======== > > This PEP introduces a language enhancement named "Power Assertion". > > The Power Assertion is inspired by a similar feature found in the > `Groovy language`_ and is an extension to the core lib's ``assert`` > keyword. > > When an assertion expression evaluates to ``False``, the output shows > not only the failure, but also a breakdown of the evaluated expression > from the inner part to the outer part. > > .. _Groovy language: > http://docs.groovy-lang.org/next/html/documentation/core-testing-guide.html#_power_assertions > > > Motivation > ========= > > Every test boils down to the binary statement "Is this true or false?", > whether you use the built-in assert keyword or a more advanced > assertion method provided by a testing framework. > When an assertion fails, the output is binary too — > "Expected x, but got y". > > There are helpful libraries like Hamcrest which give you a more > verbose breakdown of the difference and answer the question > "What exactly is the difference between x and y?". > This is extremely helpful, but it still focuses on the difference > between the values. > > Keep in mind that a given state is normally an outcome of a series of > states, that is, one outcome is a result of multiple conditions and causes. > This is where Power Assertion comes in. It allows us to better > understand what led to the failure. > > > The Community Wants This > ------------------------ > > As mentioned in the abstract, this feature was borrowed from Groovy. > It is a very popular feature within the Groovy community, also used by > projects such as `Spock`_. > > On top of that, it is very much needed in the Python community as well: > > * `Power Assertion was explicitly requested`_ as a feature in the > `Nimoy`_ testing framework > * There's a `similar feature in pytest`_ > > And when `discussed in the python-ideas`_ mailing list, the responses > were overall positive: > > * "This is cool." - Guido van Rossum > * "I was actually thinking exactly the opposite: this would more > useful in production than in testing." > - 2QdxY4RzWzUUiLuE＠potatochowder.com > * "What pytest does is awesome. I though about implementing it in the > standard compiler since seen it the first time." - Serhiy Storchaka > > .. _Spock: https://spockframework.org/ > .. _Power Assertion was explicitly requested: > https://stackoverflow.com/a/58536986/198825 > .. _similar feature in pytest: > https://docs.pytest.org/en/latest/how-to/assert.html > .. _discussed in the python-ideas: > https://mail.python.org/archives/list/python-ideas@python.org/thread/T26DR4BMPG5EOB3A2ELVEWQPYRENRXHM/ > > > Rational > ======== > > Code Example > ------------ > > :: > > class SomeClass: > def __init__(self): > self.val = {'d': 'e'} > > def __str__(self): > return str(self.val) > > sc = SomeClass() > > assert sc.val['d'] == 'f' > > This routine will result in the output: > > :: > > Assertion failed: > > sc.val['d'] == f > | | | > | e False > | > {'d': 'e'} > > > Display > ------- > > In the output above we can see the value of every part of the > expression from left to right, mapped to their expression fragment > with the pipe (``|``). > The number of rows that are printed depend on the value of each > fragment of the expression. > If the value of a fragment is longer than the actual fragment > (``{'d': 'e'}`` is longer than ``sc``), then the next value (``e``) > will be printed on a new line which will appear above. > Values are appended to the same line until it overflows in length to > horizontal position of the next fragment. > > This way of presentation is clearer and more human friendly than the > output offered by pytest's solution. > > The information that’s displayed is dictated by the type. > If the type is a constant value, it will be displayed as is. > If the type implements `__str__`, then the return value of that will > be displayed. > > > Mechanics > --------- > > Reference Implementation > '''''''''''''''''''''''' > > The reference implementation uses AST manipulation because this is > the only way that this level of involvement can be achieved by a > third party library. > > It iterates over every subexpression in the assert statement. > Subexpressions are parts of the expression separated by a lookup > (``map[key]``), an attribute reference (``key.value``) or a binary > comparison operator (``==``). > > It then builds an AST in the structure of a tree to maintain > the order of the operations in the original code, and tracks the > original code of the subexpression together with the AST code of the > subexpression and the original indices. > > It then rewrites the AST of the original expression to call a > specialised assertion function, which accepts the tree as a parameter. > > At runtime the expression is executed. If it fails, a rendering > function is called to render the assertion message as per the example > above. > > > Actual Implementation > ''''''''''''''''''''' > > To be discussed. > > In the python-ideas mailing list, Serhiy Storchaka suggests: > > It needs a support in the compiler. The condition expression should be > compiled to keep all immediate results of subexpressions on the stack. > If the final result is true, immediate results are dropped. If it is > false, the second argument of assert is evaluated and its value > together > with all immediate results of the first expression, together with > references to corresponding subexpressions (as strings, ranges or AST > nodes) are passed to the special handler. That handler can be > implemented in a third-party library, because formatting and outputting > a report is a complex task. The default handler can just raise an > AttributeError. > > > Caveats > ------- > > It is important to note that expressions with side effects are affected by > this feature. This is because in order to display this information, we must > store references to the instances and not just the values. > > > Reference Implementation > ======================== > > There's a `complete implementation`_ of this enhancement in the > `Nimoy`_ testing framework. > > It uses AST manipulation to remap the expression to a `data structure`_ > at compile time, so that it can then be `evaluated and printed`_ at > runtime. > > .. _Nimoy: https://browncoat-ninjas.github.io/nimoy/ > .. _complete implementation: > https://browncoat-ninjas.github.io/nimoy/examples/#power-assertions-beta > .. _data structure: > https://github.com/browncoat-ninjas/nimoy/blob/develop/nimoy/ast_tools/expression_transformer.py#L77 > .. _evaluated and printed: > https://github.com/browncoat-ninjas/nimoy/blob/develop/nimoy/assertions/power.py > > > Copyright > ========= > > This document is placed in the public domain or under the > CC0-1.0-Universal license, whichever is more permissive. > > > > .. > Local Variables: > mode: indented-text > indent-tabs-mode: nil > sentence-end-double-space: t > fill-column: 70 > coding: utf-8 > End: > > *Attachments:* > > - pep-9999.rst > > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/DO3ETJ4COXAFJKNYZP3IAGFX5N64CILD/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- --Guido (mobile)
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