On Thu, May 27, 2021 at 07:56:16AM -0000, Shreyan Avigyan wrote:
> This idea proposes to add a keyword
> (static, maybe?) that can create static variables that can persist
> throughout the program yet only accessible through the function they
> are declared and initialized in.
Here is a sketch of how this could work, given a function like this:
static spam, eggs
static cheese = expression
At function declaration time, the two static statements tell the
* treat spam, eggs and cheese as local variables (use LOAD_FAST instead
of LOAD_GLOBAL for lookups);
* allocate static storage for them using the same (or similar) mechanism
used for function default values;
* spam and eggs get initialised as None;
* cheese gets initialised to the value of `expression`, evaluated
at function declaration time just as default arguments are.
When the function is called:
* the interpreter automatically initialises the static variables
with the stored values;
* when the function exits (whether by return or by raising an
exception) the static storage will be updated with the current
values of the variables.
As a sketch of one possible implementation, the body of the function
represented by ellipsis `...` might be transformed to this:
# initialise statics
spam = LOAD_STATIC(0)
eggs = LOAD_STATIC(1)
cheese = LOAD_STATIC(2)
# body of the function
Couldn't you already get pretty close to this by attaching your static values to the function __dict__?
func.a = 1
Of course that is slower because there is an attribute lookup.
But could there be a decorator that links the function __dict__ to locals(), so they are intertwined?
func.b = 2
>>> func.a = 3 # dynamic update of func.__dict__
The locals dict in the function body would look something like this:
"I've never met a Kentucky man who wasn't either thinking about going home or actually going home." - Happy Chandler
One subtlety: what if the body of the function executes `del spam`? No
problem: the spam variable will become undefined on the next function
call, which means that subsequent attempts to get its value will raise
x = spam + 1
spam = 0
x = 1
I would use this static feature if it existed. +1
Same thing would happen with my idea: del a would delete a from the func.__dict__ (just like with ChainMap). But if you add it back again later, it would not be static anymore.
print(a) # fast static lookup
del a # static is deleted
a = 2 # this is local now
func.b = 3 # but this is a static