On 23 September 2016 at 13:06, Steven D'Aprano <st...@pearwood.info> wrote: > On Thu, Sep 22, 2016 at 07:21:18PM +0000, אלעזר wrote: >> "Expression" is something that you need its value right >> now, and "annotation" is something that, well, annotates the code you see >> right now. > > Right. In the case of Python, function annotations **do** have a runtime > effect: the expressions are evaluated, and the evaluated results are > assigned in function.__annotations__ and made available for runtime > introspection. > > Don't think that function annotations are **only** for the static type > checker. Python is a much richer language than that!
If folks are after a simple non-type-checking related example of annotation usage, the "begins" CLI library is a decent one: https://pypi.python.org/pypi/begins That lets you supply command line help for parameters as annotations: ============ In Python3, any function annotations for a parameter become the command line option help. For example: >>> import begin >>> @begin.start # doctest: +SKIP ... def run(name: 'What, is your name?', ... quest: 'What, is your quest?', ... colour: 'What, is your favourite colour?'): ... pass Will generate command help like: usage: holygrail_py3.py [-h] -n NAME -q QUEST -c COLOUR optional arguments: -h, --help show this help message and exit -n NAME, --name NAME What, is your name? -q QUEST, --quest QUEST What, is your quest? -c COLOUR, --colour COLOUR What, is your favourite colour? ============ It's not a substitute for something like click or argparse when it comes to more complex argument parsing, but it's a good example of the kind of simple pseudo-DSL folks have long been able to create with annotations independently of the type hinting use case. Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
