[Python-ideas] Quick idea: defining variables from functions that take the variable name
steve at pearwood.info
Tue May 31 11:08:58 EDT 2016
On Tue, May 31, 2016 at 03:39:14PM +0100, Paul Moore wrote:
> [I still prefer "call the RHS with the name of the LHS as the
> argument" over "inject the name of the LHS as the first argument of
> the call present on the RHS", btw -
Do I understand that you think that the RHS should be limited to
callables that take a single argument only?
So far we have four real use-cases:
T = TypeVar('T')
x = sympy.Symbol('x')
cls = type('cls', bases, ns)
Record = nametuple('Record', fields)
You would only support the first two cases and leave the others with the
status quo? That seems like a strange restriction to make. What problem
do you think the other two use-cases would cause that the first two
The fundamental use-case here is "any object that needs to know its own
name". Most objects need more than just a name.
If you're worried that it will be confusing that we define a callable to
take (say) three arguments:
def __init__(self, name, foo, bar):
but then call it with only two:
spanner -> Widget(foo=1, bar=2)
I think you're worrying over nothing. In fact, I played a trick on
you... I said we define a callable that takes three arguments, but in
fact I defined it with FOUR. We're constantly writing methods that take
an extra argument, self, that is provided by the compiler.
A similar argument applies to decorators:
# defined with a single argument
# called with no explicit argument (or even parens!)
And both cases can be used without compiler magic, using an unbound
method versus a bound method, decorator syntax versus calling the
decorator by hand.
So while this is magic, it is the same sort of magic we deal with
frequently in Python. So frequently that we forget just how magical it
is that the "self" param is provided automatically for us.
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