On Wed, Oct 7, 2020 at 1:46 PM Steven D'Aprano <[email protected]> wrote:
> > Recall that we already have literal expressions such as
> > >>> [1, 2, 3] # List literal
> > >>> (1, 2, 3) # Tuple literal
> > >>> {1, 2, 3} # Set literal
>
> Point of terminology: these are not literals (although informally people
> often call them that, including me on occassion). They are *displays*.
>
> One difference between a display and a literal can be seen from the
> byte-code generated:
>
> >>> import dis
> >>> dis.dis(compile('[1,2,3]', '', 'single'))
> 1 0 LOAD_CONST 0 (1)
> 2 LOAD_CONST 1 (2)
> 4 LOAD_CONST 2 (3)
> 6 BUILD_LIST 3
> 8 PRINT_EXPR
> 10 LOAD_CONST 3 (None)
> 12 RETURN_VALUE
>
> The constants 1, 2 and 3 are literals and the compiler can insert them
> directly into the code. The list [1, 2, 3] is not, the compiler has to
> insert code to create the list at runtime.
>
Be careful with this, as it's only a one-way proof. Any literal can
and will be inserted directly as a constant, but there are some
non-literals that can be as well:
>>> dis.dis(lambda x: x in {1, 2+3j, r"a\b"})
1 0 LOAD_FAST 0 (x)
2 LOAD_CONST 1 (frozenset({1, (2+3j), 'a\\b'}))
4 CONTAINS_OP 0
6 RETURN_VALUE
Complex numbers and frozen sets don't technically have literals, but
thanks to compiler magic, they can appear to. (Also, raw string
literals are a thing, but in the compiled code, what you get is just a
string object, further confusing this type of proof.)
Although when it comes to f-strings, I honestly don't know what counts
as a "literal". Is a single f-string a literal? What if two of them
abut - are they one literal or two? The compiler builds the code to do
the formatting and joining as though the parts of the string were
combined (even if they're not all f-strings).
But hey, it wouldn't be python-ideas without pedantry :)
ChrisA
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