On 2021-08-13 at 23:18:29 +1100,
Matsuoka Takuo <motogeom...@gmail.com> wrote:
> Given a subscriptable object s, the intended rule for the notation for
> getting an item of s seems that, for any expression {e}, such as
> "x, ",
> s[{e}]
> (i.e., s[x, ] if {e} is "x, ") means the same as
> s[({e})]
If e is an expression, then s[e] means s[e].
Sometimes, e happens to be a tuple, but Python doesn't create a tuple
just to call __getitem__. The following expression:
x,
is a tuple all by itself. Also:
(x,)
is that same tuple.
> (i.e., s[(x, )] in the considered case), namely, should be evaluated
> as s.__getitem__(({e})) (or s.__class_getitem__(({e})) when that
> applies). If this is the rule, then it looks simple and hence
> friendly to the user. However, there are at least two exceptions:
>
> (1) The case where {e} is the empty expression "":
There is no such thing as an "empty expression." "" is a string
containing no characters.
> The expression
> s[]
> raises SyntaxError ...
Because there is no expression (which is different from a hypothetical
"empty expression."
> ... instead of being evaluated in the same way as
> s[()] is.
() is a tuple with no elements, just as [] is a list with no elements,
and "" is a string with no elements.
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