For the record I am definitely a -1 on this. The arguments against are overwhelming and the arguments for are pretty weak. However I felt the need to rebut:
Tests don't really count, so there's a small handful here.
Tests 100% count as real use cases. If this is a pattern that would be useful in test case generation then we should be discussing that. I have worked on plenty of projects which were almost exclusively documented through tests. Being able to read and write tests fluently is as important as any other piece of code. On Sun, May 2, 2021 at 8:41 PM Chris Angelico <rosuav@gmail.com> wrote:
Rather than toy examples, how about scouring the Python standard
On Mon, May 3, 2021 at 1:00 PM David Álvarez Lombardi <alvarezdqal@gmail.com> wrote: library for some real examples?
Here are 73 of them that I found by grepping through Lib.
https://github.com/python/cpython/blob/master/Lib/email/_encoded_words.py#L9...
https://github.com/python/cpython/blob/master/Lib/email/_header_value_parser...
https://github.com/python/cpython/blob/master/Lib/email/_header_value_parser...
https://github.com/python/cpython/blob/master/Lib/email/_header_value_parser...
https://github.com/python/cpython/blob/master/Lib/email/_header_value_parser...
https://github.com/python/cpython/blob/master/Lib/email/_header_value_parser...
https://github.com/python/cpython/blob/master/Lib/lib2to3/fixes/fix_import.p...
https://github.com/python/cpython/blob/master/Lib/lib2to3/fixes/fix_next.py#...
https://github.com/python/cpython/blob/master/Lib/lib2to3/refactor.py#L235
https://github.com/python/cpython/blob/master/Lib/msilib/__init__.py#L178
https://github.com/python/cpython/blob/master/Lib/msilib/__init__.py#L290
https://github.com/python/cpython/blob/master/Lib/test/_test_multiprocessing...
https://github.com/python/cpython/blob/master/Lib/test/multibytecodec_suppor...
https://github.com/python/cpython/blob/master/Lib/test/test_audioop.py#L6
https://github.com/python/cpython/blob/master/Lib/test/test_buffer.py#L853
https://github.com/python/cpython/blob/master/Lib/test/test_code_module.py#L...
https://github.com/python/cpython/blob/master/Lib/test/test_code_module.py#L...
https://github.com/python/cpython/blob/master/Lib/test/test_codeccallbacks.p...
https://github.com/python/cpython/blob/master/Lib/test/test_codeccallbacks.p...
https://github.com/python/cpython/blob/master/Lib/test/test_codeccallbacks.p...
https://github.com/python/cpython/blob/master/Lib/test/test_codecs.py#L149
https://github.com/python/cpython/blob/master/Lib/test/test_codecs.py#L1544
https://github.com/python/cpython/blob/master/Lib/test/test_codecs.py#L1548
https://github.com/python/cpython/blob/master/Lib/test/test_codecs.py#L1552
https://github.com/python/cpython/blob/master/Lib/test/test_codecs.py#L1556
https://github.com/python/cpython/blob/master/Lib/test/test_codecs.py#L1953
https://github.com/python/cpython/blob/master/Lib/test/test_codecs.py#L1991
https://github.com/python/cpython/blob/master/Lib/test/test_decimal.py#L1092
https://github.com/python/cpython/blob/master/Lib/test/test_decimal.py#L5346
https://github.com/python/cpython/blob/master/Lib/test/test_email/test_email...
https://github.com/python/cpython/blob/master/Lib/test/test_email/test_email...
https://github.com/python/cpython/blob/master/Lib/test/test_fileinput.py#L91
https://github.com/python/cpython/blob/master/Lib/test/test_fileinput.py#L92
https://github.com/python/cpython/blob/master/Lib/test/test_fileinput.py#L93
https://github.com/python/cpython/blob/master/Lib/test/test_fileinput.py#L94
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L360
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L366
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L372
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L378
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L384
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L391
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L397
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L403
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L409
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L415
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L421
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L427
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L433
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L455
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L457
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L459
https://github.com/python/cpython/blob/master/Lib/test/test_gettext.py#L461
https://github.com/python/cpython/blob/master/Lib/test/test_long.py#L305
https://github.com/python/cpython/blob/master/Lib/test/test_lzma.py#L1049
https://github.com/python/cpython/blob/master/Lib/test/test_lzma.py#L1087
https://github.com/python/cpython/blob/master/Lib/test/test_random.py#L914
https://github.com/python/cpython/blob/master/Lib/test/test_random.py#L921
https://github.com/python/cpython/blob/master/Lib/test/test_random.py#L927
https://github.com/python/cpython/blob/master/Lib/test/test_random.py#L933
https://github.com/python/cpython/blob/master/Lib/test/test_random.py#L968
https://github.com/python/cpython/blob/master/Lib/test/test_re.py#L1013
https://github.com/python/cpython/blob/master/Lib/test/test_strtod.py#L226
https://github.com/python/cpython/blob/master/Lib/test/test_ucn.py#L192 https://github.com/python/cpython/blob/master/Lib/test/test_ucn.py#L65
https://github.com/python/cpython/blob/master/Lib/test/test_unicodedata.py#L...
https://github.com/python/cpython/blob/master/Lib/test/test_zipfile.py#L1833
https://github.com/python/cpython/blob/master/Lib/tkinter/__init__.py#L268
https://github.com/python/cpython/blob/master/Lib/unittest/test/test_asserti...
https://github.com/python/cpython/blob/master/Lib/unittest/test/test_case.py...
https://github.com/python/cpython/blob/master/Lib/urllib/parse.py#L907
https://github.com/python/cpython/blob/master/Lib/xml/etree/ElementTree.py#L...
Tests don't really count, so there's a small handful here. I haven't looked at them all. Some of them definitely could be done this way, but the best way to make your point is to show the current code and your proposed alternative, and show how the new syntax improves things. Not just "it could be done this way", but "this way looks massively better".
Second, f-strings do not restrict the normal usage of strings for freeform text content (apart from making the curly brace characters special).
Not to nit-pick too much, but the following is a valid string but not a valid f-string.
s = f"This is a valid string but invalid f-string {}" File "<stdin>", line 1 s = f"This is a valid string but invalid f-string {}" ^ SyntaxError: f-string: empty expression not allowed
That's exactly because the curly braces are special. Not sure your point here?
Would readers see any merit in a syntax like the following?
dirty = "f8sjGe7" clean = str(char for char in dirty if char in string.ascii_letters) clean 'fsjGe'
Or would it stray too far from the behavior of the str() constructor in general?
The str constructor is also the generic "turn anything into a string" function. If it were not for that, I'd say it's fairly reasonable; but I don't want to see a genexp automatically pump itself and join the results just because someone printed it out. But if you wanted to make a dedicated constructor, eg str.from_substrings(iterable), that would definitely be viable. Would it be useful? Not sure.
I don't intend to reinvent strings, I only mean to leverage an already existing means of signifying modified string construction syntax (prefixes) to align str construction syntax with the comprehensions available for the other most common builtin iterables, avoid the notoriously unintuitive "".join syntax, and improve readability.
Yes, "".join() takes some learning, but if that's the problem being solved, I'd much rather look into simpler solutions. I'd really like to see str.__rmul__() accept any iterable and join it, as mentioned earlier (or maybe that was in a related thread):
class Str(str): ... __rmul__ = str.join ... ["Hello", "world"] * Str(" ") 'Hello world'
or, if it became part of the core:
["Hello", "world"] * " "
But in terms of embedding a join expression in the middle of an f-string (NOT cases where the join is the entire expression), I do think it'd be nice to have a mutator syntax that iterates over the thing, formatting each element according to the given definition, and outputting them all together - effectively equivalent to joining with an empty string.
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