Nice!
On Sun, Oct 25, 2020 at 9:59 PM Dennis Sweeney
What if the mapping assignment were more harmonious with the pattern matching PEP? Something like this:
items = {'eggs': 2, 'cheese': 3, 'spam': 1} {'eggs': eggs, 'spam': i_dont_need_to_name_this_spam, **rest} = items assert i_dont_need_to_name_this_spam == 1 assert eggs == 2 and cheese == 3 assert rest == {'cheese': 3}
The keys here could be arbitrary hashables and the "values" could be arbitrary assignment targets (assigned all-or-nothing). This wouldn't need the right-hand-side double-star, and I think it more closely resembles the sequence unpacking assignment syntax. You can assign to a (thing that looks like a) tuple or to a (thing that looks like a) list or to a sequence subscript or object attribute, why not be able to assign to a (thing that looks like a) dictionary? This also avoids polluting the local namespace in case one of your keys is the string "range" or something. It also feels less magical to me, albeit more verbose.
Calls to a hypothetical parse/sscanf function could closely mirror some str.format() calls:
text = "{a}, {b}, {c}".format(**{'a': a0, 'b': b0, 'c': c0}) {'a': a1, 'b': b1, 'c': c1} = "{a}, {b}, {c}".parse(text) assert (a1, b1, c1) == (a0, b0, c0)
Alternative positional parsing would be useful as well, as in:
text = "{}, {}, {}".format(a0, b0, c0) a1, b1, c1 = "{}, {}, {}".parse(text) assert (a1, b1, c1) == (a0, b0, c0)
This way, pattern.format() and pattern.parse() would be trying to be inverses of each other (as much as is reasonable, probably limited to parsing strings, floats and ints).
Then maybe people could get used to a format-string-like mini-language for parsing, and eventually, the f-string assignment might be better received, and we could propose something like
text = f"{a0}, {b0}, {c0}" f"{a1}, {b1}, {c1}" = text assert (a1, b1, c1) == (a0, b0, c0)
as well, where we lose some of the flexibility but gain better D.R.Y. and more visual locality, useful in the simple cases. I see the potential for a strong analogy:
positional format() : keyword-based format() : fstrings :: positional parse() : keyword-based parse(): assignment to fstrings _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@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/H5252O... Code of Conduct: http://python.org/psf/codeofconduct/
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