On 2020-09-16 21:52, Dennis Sweeney wrote:
TL;DR: I propose the following behavior:
>>> s = "She turned me into a newt."
>>> f"She turned me into a {animal}." = s
>>> animal
'newt'
>>> f"A {animal}?" = s
Traceback (most recent call last):
File "<pyshell#2>", line 1, in <module>
f"A {animal}?" = s
ValueError: f-string assignment target does not match 'She turned me into
a newt.'
>>> f"{hh:d}:{mm:d}:{ss:d}" = "11:59:59"
>>> hh, mm, ss
(11, 59, 59)
I don't like this at all. It looks like assigning to a literal, which
is weird. Also, it hides the assignment target within a string of
potentially unbounded length and complexity, which makes it difficult to
reason about code because it's hard to see when variables are being
assigned to. It also introduces a whole host of questions about the
details of the parsing (i.e., how does the greediness work if the
pattern is something like "{one} {two} {three} {four}" and the string to
be parsed is five or ten words).
I think a better approach for something like this would be a .parse()
method of some sort on strings, sort of like the inverse of .format().
It would parse a given string according to the format string and return
a dict with the mappings (just as format can take a dict in and return
the string with the substitutions made). So it would be like:
>>> pattern = "That {animal} is really {attribute}."
>>> d = pattern.parse("That snake is really powerful.")
>>> d['animal']
'snake'
>>> d['attribute']
'powerful'
This wouldn't let you assign the results into local variables, but I
think that's a good thing. Creating local variables "programmatically"
is not a good idea; it's better to use a dict.
--
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is no
path, and leave a trail."
--author unknown
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