Hey everyone,
I meant to say, I agree with the two of you, actually. `_` as a variable
name is terrible, but it /can/ be used all the same ; on the other hand,
wildcards should not be legitimate variable names, to prevent
misunderstandings / accidents / bugs.
Had I taken part in the discussion aroud pattern matching, I would have
liked the `else` syntax better : having a special syntax for special
cases seems clearer, cleaner, and safer.
Another option that comes to mind is using `*` as the wildcard. There is
already a precedent for using `*` alone, e.g. in `import` statements. In
this case, it means "import everything from this module", as opposed to
listing the items you need. I can easily see the parallel with `match`
statements, thus making it intuitive to learn and use this new syntax.
Anyway, yes, `_` as joker has flaws, the biggest one being to be a
resolvable variable name ; what is the expected behaviour when running a
script that has (even accidentally) a viariable named `_` ? The question
is even more pressing in REPL, since there /is/ necessarily such a
variable !
I guess it's too late to change anything, though, so we'll have to get
used to it...
From https://docs.python.org/3.10/whatsnew/3.10.html
<https://docs.python.org/3.10/whatsnew/3.10.html>:
def http_error(status):
match status:
case 400:
return "Bad request"
case 404:
return "Not found"
case 418:
return "I'm a teapot"
case _:
return "Something's wrong with the Internet"
The wildcard idea looks just wrong and confusing. What if I want to
use it as a variable and match against it like _ = 504? This is how it
should be done:
def http_error(status):
_ = 504
match status:
case 400:
return "Bad request"
case 404:
return "Not found"
case 418:
return "I'm a teapot"
case _:
return "Gateway Timeout"
else:
return "Something's wrong with the Internet"
Don't do that.
There is a very strong convention in Python that a single underscore is
to be used for two purposes (and a third in the interactive interpreter
only):
(1) For "don't care" variables; anything that you don't care about and
aren't intending to use should be named `_`.
first, *_, last = sequence
This tells me that I am only using the first and last items, everything
else is ignored.
(2) For internationalisation. This is a convention that comes from other
languages, but it is so widespread that we're kinda stuck with it.
print(_("Try again."))
By convention, the underscore function is used to translate messages
into the current location's language.
(3) And in the interactive interpreter, underscore is a special variable
which captures the previous result. This doesn't work in scripts.
>>> 5 + 4
9
>>> _*10
90
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